SE539430C2

SE539430C2 - Method and system for facilitating steering of a vehicle while driving along a road

Info

Publication number: SE539430C2
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: 2017-09-19
Also published as: DE112016005072T5; SE1551565A1; DE112016005072B4; WO2017095301A1

Description

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

BACKGROUND ART In order to facilitate steering during driving along a road systems for controlling the torque are utilized. Such systems include active steering systems which for example are able to make the steering wheel feel stiffer at higher vehicle speed to get the steering stable when driving on a straight road. 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 configuration of the road, and/or lateral wind will require additional force from the driver in order to keep the vehicle on the road.

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

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

There is however a need for simplifying the way of providing a basis for influencing 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 facilitating steering of a vehicle during driving along a road which provides an easy and efficient way of compensating the steering of the vehicle due to the curvature of the road.

An object of the present invention is to provide a method for facilitating steering of a vehicle during driving along a road which provides an easy and efficient way of compensating the steering of the vehicle due to external forces.

Another object of the present invention is to provide a system for facilitating steering of a vehicle during driving along a road which provides an easy and efficient way of compensating the steering of the vehicle due to the curvature of the road.

Another object of the present invention is to provide a system for facilitating steering of a vehicle during driving along a road which provides an easy and efficient way of compensating the steering of the vehicle due to external forces.

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

Specifically an object of the invention is achieved by a method for facilitating steering of a vehicle during driving along a road. The method comprises the steps of: determining the vehicle speed; determining the curvature of the road; and determining a required yaw rate for the vehicle based upon the thus determined vehicle speed and curvature of the road. The method further comprises determining 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 torque and yaw rate of the vehicle.

The vehicle speed is determined continuously or intermittently during drive of the vehicle. The curvature of the road is determined continuously or intermittently during drive of the vehicle. The required yaw rate determined by means of the thus determined vehicle speed and curvature of the road corresponds to the yaw rate required for the vehicle to keep the vehicle in the direction of the curvature or the road. More specifically, according to an embodiment, the required yaw rate determined by means of the thus determined vehicle speed and curvature of the road corresponds 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 vehicle essentially corresponds to a direction corresponding to the curvature of the road at the location of the vehicle.

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

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

Hereby an easy and efficient method for compensating the steering of the vehicle due to external forces is facilitated. For automated steering functions such as lane keep assist, compensation due to curvature of the road will prevent the vehicle from bouncing against the boundary of the lane within which the vehicle is intended to be kept. For manual driving, the driver will have a much increased comfort and does not have to compensate for effects due to curvature of the road.

According to an embodiment the method comprises the step of compensating the steering torque of the vehicle based upon said determined curvature compensation torque.

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

According to an embodiment the method further comprises the steps of: detecting the yaw rate of the vehicle; modelling the yaw rate of the vehicle based upon the steering torque of the vehicle; comparing the detected and modelled yaw rate; determining the influence of external forces on the yaw rate based on said comparison of detected and modelled yaw rate, said external 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 of external forces on the yaw rate and said gain function determining an external force compensation torque for compensating the steering torque of the vehicle due to influence of external forces.

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

The gain function comprises static gain. In most drive situations comprising normal driving along a road, the gain function, by means of which the external force compensation torque is determined, is a static gain which efficiently facilitates obtaining the external force compensation torque utilizing the fact that the change of the external forces, e.g. road banking, is normally very small over a certain time/distance and may be assumed essentially static/non-changing. This provides for a very efficient compensation of the steering torque of the vehicle due to influence of external forces.

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

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

According to an embodiment of the method the result of said comparison between the detected and modelled yaw rate is filtered so as to avoid influence of rapid changes. Hereby a more efficient compensation is obtained, further improving the comfort during driving along a road in that rapid changes are avoided.

According to an embodiment the method further comprises the step of determining a compensation torque based upon said determined curvature compensation torque and said determined external force compensation torque; and compensating the steering torque based upon said determined compensation torque.

Hereby the influence of both curvature and external effects are taken into account, wherein steering of the vehicle is facilitated in an efficient way. By thus compensating the steering torque of the vehicle based upon said determined compensation torque comfort for the operator of the vehicle will be increased which may prevent stiff shoulder, stiff neck and the like. According to an embodiment of the method the modelled yaw rate is obtained via a transfer function. By applying a transfer function an efficient way of obtaining the modelled yaw rate is facilitated. The transfer function is configured to transfer the steering torque to the modelled yaw rate. The transfer function comprises calculating what the yaw rate would be after a certain time based upon a certain steering torque, i.e. a certain torque applied on the steering wheel of the vehicle. The method thus comprises the step of obtaining the modelled yaw rate from the steering torque by means of a transfer function.

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

According to an embodiment of the method said gain function comprises a static gain. The static gain provides information regarding the torque that needs to be maintained in order to maintain a constant yaw rate. In most drive situations comprising normal driving along a road, the gain function, by means of which the curvature compensation torque is determined based upon said determined required yaw rate, is a static gain which efficiently facilitates obtaining the compensation torque utilizing the fact that the change of the curvature of the road and external effects are normally very small over a certain time/distance and may be assumed essentially static/non-changing, such a static gain therefor being efficient for obtaining the compensation torque. 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 facilitating steering of a vehicle during driving along a road,characterized bymeans for determining the vehicle speed; means for determining the curvature of the road; means for determining a required yaw rate for the vehicle based upon the thus determined vehicle speed and curvature of the road; means for determining 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 torque and yaw rate of the vehicle.

According to an embodiment the system further comprises means for detecting the yaw rate of the vehicle; means for modelling the yaw rate of the vehicle based upon the steering torque of the vehicle; means for comparing the detected and modelled yaw rate; means for determining the influence of external forces on the yaw rate based on said comparison of detected and modelled yaw rate, said external 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 means for determining an external force compensation torque for compensating the steering torque of the vehicle due to influence of external forces based upon the determined influence of external forces on the yaw rate and said gain function.

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

According to an embodiment the system further comprises means for determining a compensation torque based upon said determined curvature compensation torque and said determined external force compensation torque; 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 obtained via a transfer function.

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

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

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

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

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

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

Specifically an object of the invention is achieved by a computer program product 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 the accompanying drawings, wherein 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 the present 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 being subjected to external forces comprising on cross sloped configuration of the road and influence of lateral wind; Fig. 4 schematically illustrates a steering configuration of a vehicle and related torques according to an embodiment of the invention; Fig. 5 schematically illustrates a block diagram of a system for facilitating steering 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 a compensation torque for facilitating steering of a vehicle during driving along a road according to an embodiment of the present invention; Fig. 7 schematically illustrates a block diagram of a system for providing a compensation torque for facilitating steering of a vehicle during driving along a road according to an embodiment of the present invention; Fig. 8 schematically illustrates a block diagram of a method for facilitating steering of a vehicle during driving along a road according to an embodiment of the present invention; and Fig. 9 schematically illustrates a computer according to an embodiment of the present invention.

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

Hereinafter the term "steering torque" refers to the total input torque acting on the 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 assistance torque being a boost of the driver torque. The steering torque further comprises an external torque being a demanded torque for steering the vehicle. Fig. 4 illustrates an example of a steering configuration and how the steering torque relates to driver torque and external torque.

Hereinafter the term "curvature" refers to the conventional definition of curvature 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 the present invention. The exemplified vehicle 1 is a heavy vehicle in the shape of a truck. The vehicle according to the present invention could be any suitable vehicle such as a bus or a car. The vehicle comprises a system I, II, III 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 a curve of a road R. The curvature of the road R affects the behaviour of the vehicle requiring steering compensation from the driver of the vehicle 1. Fig. 3 schematically illustrates a rear view of the vehicle 1 in fig. 1 being subjected to external forces. The vehicle has wheels of which left and right rear wheels LR, RR are shown. The external forces comprise cross sloped configuration of the road R on which the vehicle 1 is travelling. The cross sloped configuration of the road R is called road banking, the road R having a certain inclination a such that water is allowed to run off the road. The external forces comprise influence of lateral wind A. The external forces may also comprise a flat tire on a wheel of the vehicle.

The present invention provides method and system for facilitating steering of a vehicle during driving along a road so as to compensate for such external forces. This is achieved by detecting the yaw rate of the vehicle and modelling the yaw rate of the vehicle and comparing the detected and modelled yaw rate. The modelled yaw rate is based upon the steering torque of the vehicle. The influence of external forces on the yaw rate is determined based on the comparison of detected and modelled yaw rate. A compensation torque for compensating the steering torque of the vehicle is then determined based upon the determined influence of external forces on the 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 and related torques according to an embodiment of the invention.

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

The driver torque DT is provided by applying torque to the steering wheel SW. 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 an assistance torque AT which represents a boost of the driver torque in order to obtain a good feeling for the driver by steering the vehicle. The assistance torque AT may vary with vehicle speed. The assistance torque AT is provided a specific feeling during steering of the vehicle such that by low speeds a high boost is provided to facilitate drive at low speeds and at high speed a low gain is provided in order to stiffen the steering wheel SW.

An external torque ET may according to an embodiment be provided which is added to the assistance torque AT. The external torque ET would according to a variant have the effect that if the driver lets go of the steering wheel SW it is only the external toque ET that provides the steering. During drive in curve the external torque ET may be added in order to follow the curvature. The external torque may correspond to a compensation torque determined in accordance with the present invention. The external torque ET may also comprise a torque based on a lane keep assistance function.

If 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 torque of 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 LA connected to the steering column SC. The steering torque ST is the driver torque DT + the assistance torque AT and where applicable also + the external torque ET. The steering torque ST is thus determined by means of the torque sensor TS and the gain G and by adding the possible external torque ET. The external torque ET is a demanded torque and thus known and provided from an electronic control unit.

Fig. 5 schematically illustrates a system I for facilitating steering of a vehicle during driving along a road according to an embodiment of the present invention.

The system I comprises an electronic control unit 100.

The system I comprises means 112 for determining the vehicle speed. The means 112 for determining the vehicle speed comprises according to an embodiment the speedometer of the vehicle. The vehicle speed is determined continuously or intermittently during drive of the vehicle.

The system I comprises means 114 for determining the curvature of the road. The means 114 for determining the curvature of the road may comprise any suitable means for determining the curvature of the road. The means 114 for determining the curvature of the road comprises according to an embodiment a global positioning system, GPS, for continuously or intermittently determining the position of the vehicle and map data comprising information about the curvature of the road. The means 114 for determining the curvature of the road comprises according to an embodiment detecting means such as one or more camera units for detecting road marks and/or crash barriers and/or side of the road so as to continuously or intermittently determining the curvature of the road in connection to the position of the vehicle. The means 114 for determining the curvature of the road comprises according to an embodiment detection means for detecting a vehicle in front of the vehicle driving in the same direction for determining the curvature of the road on which 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 for the vehicle based upon the thus determined vehicle speed and curvature of the road. The means 120 for determining a required yaw rate for the vehicle based upon the thus determined vehicle speed and curvature of the road comprises calculation means. The means 120 for determining a required yaw rate for the vehicle based upon the thus determined vehicle speed and curvature of the road is according to an embodiment comprised in the electronic control unit 100.

The required yaw rate determined by means of the thus determined vehicle speed and curvature of the road corresponds to the yaw rate required for the vehicle to keep the vehicle in the direction of the curvature or the road. More specifically, according to an embodiment, the required yaw rate determined by means of the thus determined vehicle speed and curvature of the road corresponds 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 vehicle essentially corresponds to a direction corresponding to the curvature of the road at the location of the vehicle.

The system I comprises means 130 for determining 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 torque and yaw rate of the vehicle. The means 130 for determining a curvature compensation torque comprises calculation means. The means 130 for determining a curvature compensation torque is according to an embodiment comprised in the electronic control unit 100.

The gain function comprises static gain. The static gain is the gain provided by the system when the time goes to infinity. The static gain is used for determining the required steering torque in order to compensate for the error corresponding to the difference between the detected and modelled yaw rate.

According to an embodiment of the system the gain function and hence the static gain is arranged to be obtained via a transfer function of a modelling means.

In most drive situations comprising normal driving along a road, the gain function, by means of which the curvature compensation torque is determined based upon said determined required yaw rate, is a static gain which efficiently facilitates obtaining the curvature compensation torque utilizing the fact that the change of the curvature of the road is normally very small over a certain time/distance and may be assumed essentially static/non-changing.

The system I comprises means 142 for determining the steering torque. The means 142 for determining the steering torque may comprise any suitable torque sensor for determining the steering torque. The means 142 for determining the steering torque may comprise the electronic control unit. The means 142 for determining the steering torque may be arranged to determine the steering torque in accordance with the determination of the steering torque 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 detector unit for detecting the yaw rate. The detector unit is configured to detect/measure the rotation in the x/y-plane. The detector unit is according to an embodiment a gyro configured to sense the rotation in the x/y-plane. The detection 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 of the vehicle. The modelling means 150 is arranged to model the yaw rate based upon the steering torque of the vehicle. The modelling means 150 is arranged to provide a model wherein a certain torque gives a certain yaw angle and how quickly it affects yaw rate. The modelling means 150 is according to an embodiment a dynamic model built up by means of measurements.

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

The transfer function of the modelling means 150 is configured to provide a relationship between steering torque and yaw rate. The transfer function of the modelling means 150 is configured to provide said gain function and hence said static gain relating to the torque required for obtaining a constant yaw rate. The transfer function of the modelling means 150 is configured to provide a moment of inertia relating to the rate of change of the yaw rate due to turning of the steering wheel of the vehicle.

The system I comprises means 160 for comparing the detected and modelled yaw rate. The means 160 for comparing the detected and modelled yaw rate comprises calculation means for calculating the difference between the detected and modelled yaw rate. The means 160 is according to an embodiment comprised in the electronic control unit 100.

The system I comprises filtering means F for filtering the result of said comparison between the detected and modelled yaw rate so as to avoid influence of rapid changes. The comparison is thus performed during a certain time span and by filtering the result such rapid changes can be avoided.

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

According to an embodiment of the system said 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.

If there is no difference in the comparison of detected and modelled yaw rate there is likely no influence of external forces. This would be the case if the road is essentially horizontal and there are no lateral wind affecting the vehicle.

The system I comprises means 180 for determining an external force compensation torque for compensating the steering torque of the vehicle based upon the determined influence of external forces on the yaw rate and said gain function.

The gain function comprises static gain. In most drive situations comprising normal driving along a road, the gain function, by means of which the external force compensation torque is determined, is a static gain which efficiently facilitates obtaining the external force compensation torque utilizing the fact that the change of the external forces, e.g. road banking, is normally very small over a certain time/distance and may be assumed essentially static/non-changing.

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

The system I comprises means 192 for determining a compensation torque based upon said determined curvature compensation torque and said determined external force compensation torque. The means 192 for determining a compensation torque comprises calculation means. The means 192 for determining a compensation torque is according to an embodiment comprised in the electronic control unit 100.

The system I comprises means 194 for compensating the steering torque based upon said determined compensation torque. The means 194 for compensating the steering torque based upon said determined compensation torque is arranged to be added/subtracted so as to compensate for the torque provided by the external forces such that only the vehicle related torque/driver torque affects the driving of the vehicle such that the vehicle is not affected by the external forces. Thus, the experience for the driver will be the same as if there were no external forces, e.g. no lateral wind and no banked road.

According to an embodiment external forces could also be detected.

According to an embodiment the external force relating to cross sloped configuration of the road, i.e. road banking is detected by means of detecting the lateral acceleration. The yaw rate due to cross sloped configuration of the road can thus be determined by calculation by dividing the thus detected lateral acceleration with the vehicle speed and subtracting the measured yaw rate.

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 for determining the vehicle speed via a link 12. The electronic control unit 100 is via the link 12 arranged to receive a signal from said means 112 representing data for vehicle speed.

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

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

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

The electronic control unit 100 is operably connected to the means 120 for determining a required yaw rate for the vehicle based upon the thus determined vehicle speed and curvature of the road via a link 20c. The electronic control unit 100 is via the link 20c arranged to receive a signal from said means 120 representing data for required yaw rate for the.

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

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

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

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

The electronic control unit 100 is operably connected to the modelling means 150 for modelling the yaw rate of the vehicle via a link 50a. The electronic control unit 100 is via the link 50a arranged to send a signal to said means 150 representing data for the steering toque.

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

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

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

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

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

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

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

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

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

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

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

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

The electronic control unit 100 is operably connected to the means 192 for determining a compensation torque based upon said determined curvature compensation torque and said determined external force compensation torque via a link 92a. The electronic control unit 100 is via the link 92a arranged to send a signal to said means 192 representing data for influence of external forces on the yaw rate.

The electronic control unit 100 is operably connected to the means 192 for determining a compensation torque based upon said determined curvature compensation torque and said determined external force compensation torque via a link 92b. The electronic control unit 100 is via the link 92b arranged to send a signal to said means 192 representing data for static gain from the transfer function.

The electronic control unit 100 is operably connected to the means 192 for determining a compensation torque based upon said determined curvature compensation torque and said determined external force compensation torque via a link 92c. The electronic control unit 100 is via the link 92c arranged to receive a signal from said means 192 representing data for compensation torque for compensating the steering torque of the vehicle. The electronic control unit 100 is operably connected to the means 194 for compensating the steering torque based upon said determined compensation torque via a link 94a. The electronic control unit 100 is via the link 94a arranged to send a signal to said means 194 representing data for compensation torque for compensating the steering torque of the vehicle.

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

Fig. 6 schematically illustrates a block diagram of a system II for providing a curvature compensation torque for facilitating steering of a vehicle during driving along a road according to an embodiment of the present invention.

The system II could be a subsystem to the system I. The system II may comprise parts of the system I. The system II could be a subsystem to the system III described with reference to fig. 7.

The system II comprises means 212 for determining the vehicle speed. The means 212 for determining the vehicle speed comprises according to an embodiment the speedometer of the vehicle. The vehicle speed is determined continuously or intermittently during drive of the vehicle.

The system II comprises means 214 for determining the curvature of the road. The means 214 for determining the curvature of the road may comprise any suitable means for determining the curvature of the road. The means 214 for determining the curvature of the road may be determined accordance with the means 214 for determining the curvature of the road described with reference to fig. 5. The curvature of the road is determined continuously or intermittently during drive of the vehicle.

The system II comprises means 220 for determining a required yaw rate for the vehicle based upon the thus determined vehicle speed and curvature of the road. The means 220 for determining a required yaw rate for the vehicle based 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 to the means 212 for determining the vehicle speed via a link 220a. The means 220 is via the link 220a arranged to receive data representing vehicle speed.

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

The system II comprises means 252 for providing a gain function. The means 252 for providing a gain function is arranged to provide the gain function based on steering torque and yaw rate of the vehicle. The means 252 is arranged to receive a signal via a link 252a representing data for steering torque of the vehicle. The means 252 is arranged to receive a signal via a link 252b representing data for yaw rate of the vehicle, the data for yaw rate being 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 the static gain. The parameter estimation means may comprise a static gain estimated by a certain parameter based on vehicle configuration such as vehicle weight, wheel base and the like and may according to an embodiment be a fixed value.

The means 252 comprises according to an embodiment a transfer function, wherein the gain function and hence the static gain is configured to be provided by means of the transfer function.

The means 252 is according to an embodiment comprised in a modelling means 250 comprising said transfer function. The modelling means 250 may be configured according to the modelling means 150 described with reference to fig. 5. The modelling means 250 may be configured according to the modelling means 350 described with reference to fig. 7.

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

The system II comprises means 230 for determining 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 torque and yaw rate of the vehicle.

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

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

The means 230 for determining a curvature compensation torque is arranged to 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 thus obtained curvature compensation torque may via a link 230c be sent to a means for compensating the steering torque. Compensation of the steering torque is thus based upon the determined curvature compensation torque. The determined curvature compensation torque may be added/subtracted to the steering torque so as to compensate for the torque provided 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 III for providing a compensation torque for facilitating steering of a vehicle during driving along a road according to an embodiment of the present invention.

The system III could be a subsystem to the system I. The system III may comprise parts of the system I. The system III is arranged to provide generally the same information as the system I.

The system III comprises means 312 for determining the vehicle speed. The means 312 for determining the vehicle speed comprises according to an embodiment the speedometer of the vehicle. The vehicle speed is determined continuously or intermittently during drive of the vehicle.

The system III comprises means 314 for determining the curvature of the road. The means 314 for determining the curvature of the road may comprise any suitable means for determining the curvature of the road. The means 314 for determining the curvature of the road may be determined accordance with the means 314 for determining the curvature of the road described with reference to fig. 5. The curvature of the road is determined continuously or intermittently during drive of the vehicle.

The system III comprises means 320 for determining a required yaw rate for the vehicle based upon the thus determined vehicle speed and curvature of the road. The means 320 for determining a required yaw rate for the vehicle based upon the thus determined vehicle speed and curvature of the road comprises calculation means.

The means 320 for determining a required yaw rate is operably connected to the means 312 for determining the vehicle speed via a link 320a. The means 320 is via the link 320a arranged to receive data representing vehicle speed.

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

The system III comprises a transfer function G(z) configured to provide a relationship between steering torque and yaw rate. The transfer function G(z) is part of a modelling means 350. The transfer function G(z) is thus comprised in the modelling means 350 and is configured to transfer the steering torque to a yaw rate. The transfer function G(z) of the modelling means 350 is configured to provide a gain function relating to steering torque and yaw rate of the vehicle. The gain function comprise a static gain. The transfer function G(z) of the modelling means 350 is configured to provide a static gain relating to steering torque and yaw rate of the vehicle.

The system III comprises means 330 for determining 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 torque and yaw rate of the vehicle.

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

The means 330 for determining a curvature compensation torque for compensating the steering torque of the vehicle due to influence of curvature is 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 function, the data for gain function according to a preferred embodiment comprising data for static gain. The static gain is the gain provided by the system when the time goes to infinity. The static gain is used for determining the required torque in order to compensate for curvature of the road.

The means 330 for determining a curvature compensation torque is arranged to 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 the vehicle. The modelling means 350 is arranged to model the yaw rate based upon the steering torque of the vehicle. The modelling means 350 is arranged to receive a signal via a link 350a representing data for steering torque.

The modelling means 350 is arranged to provide a model wherein a certain torque gives a certain yaw angle and how quickly it affects yaw rate. The modelling 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 would be within a certain time based on a certain steering torque as input via the link 350a.

The static gain provided by the transfer function G(z) of the modelling means 350 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 to provide a moment of inertia relating to the rate of change of the yaw rate due to turning of the steering wheel of the vehicle.

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

The means 360 for comparing the detected and modelled yaw rate is arranged to receive a signal via a link 220a representing detected yaw rate. The means 360 for comparing the detected and modelled yaw rate is arranged to receive a signal via a link 350b representing the modelled yaw rate.

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

The system III comprises filtering means F for filtering the result of said comparison between the detected and modelled yaw rate so as to avoid influence of rapid changes.

The filtering means F is arranged to receive a signal via a link 360c representing data for result of comparison between the detected and modelled yaw rate.

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

The influence of external forces on the yaw rate is determined based on said comparison of detected and modelled yaw rate. If there is a difference in the comparison of detected and modelled yaw rate the difference is assumed to relate 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 III comprises means 380 for determining an external force compensation torque for compensating the steering torque of the vehicle based upon the determined influence of external forces on the yaw rate.

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

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

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

The means 380 for determining an external force compensation torque is arranged to process the data for static gain and the data for result of comparison between the detected and modelled yaw rate so as to obtain the external torque compensation torque.

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

The means 392 for determining a compensation torque is operably connected to the means 330 for determining a curvature compensation torque via a link 330c. The means 392 for determining a compensation torque is via the link 330c arranged to receive a signal representing data for curvature compensation torque.

The means 392 for determining a compensation torque is operably connected to the means 380 for determining an external force compensation torque via a link 380a. The means 392 for determining a compensation torque is via the link 380a arranged to receive a signal representing data for external force compensation torque.

The means 392 for determining a compensation torque is arranged to process the data for curvature compensation torque and the data for external force compensation torque so as to obtain the compensation torque.

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

Fig. 8 schematically illustrates a block diagram of a method for facilitating steering 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 vehicle during driving along a road comprises a step S1. In this step the vehicle speed is determined.

According to the embodiment the method for facilitating steering of a vehicle during driving along a road comprises a step S2. In this step the curvature of the road is determined.

According to the embodiment method for facilitating steering of a vehicle during driving along a road comprises a step S3. In this step a required yaw rate for the vehicle is determined based upon the thus determined vehicle speed and curvature of the road.

According to the embodiment the method for facilitating steering of a vehicle during driving along a road comprises a step S4. In this step a curvature compensation torque for compensating the steering torque of the vehicle due to influence of curvature is determined based upon said determined required yaw rate and a gain function relating to steering torque and yaw rate of the vehicle.

The gain function may for certain situations facilitate taking certain dynamic behaviour into account, e.g. when there are passages of quick changes of the curvature along the road. The gain function may also be dependent on vehicle speed, wheel angle, load on front shaft and/or other parameters that may affect which gain, e.g. static gain, that is applicable at a certain moment of time. Such parameters may be modelled by means of a modelling means. Hereby an easy and efficient method for compensating the steering of the vehicle due to external forces is facilitated. For automated steering functions such as lane keep assist, compensation due to curvature of the road by means of the curvature compensation torque will prevent the vehicle from bouncing against the boundary of the lane within which the vehicle is intended to be kept. For manual driving, the driver will have a much increased comfort and does not have to compensate for effects due to curvature of the road.

Hereby the influence of both curvature and external effects are taken into account, wherein steering of the vehicle is facilitated in an efficient way. By thus compensating the steering torque of the vehicle based upon said determined compensation torque comfort for the operator of the vehicle will be increased which may prevent stiff shoulder, stiff neck and the like.

According to an embodiment of the method the modelled yaw rate is obtained via a transfer function. By applying a transfer function an efficient way of obtaining the modelled yaw rate is facilitated. The transfer function is configured to transfer the steering torque to the modelled yaw rate. The transfer function comprises calculating what the yaw rate would be after a certain time based upon a certain steering torque, i.e. a certain torque applied on the steering wheel of the vehicle. The method thus comprises the step of obtaining the modelled yaw rate from the steering torque by means of a transfer function.

With reference to figure 9, a diagram of an apparatus 500 is shown. The control unit 100 described with reference to fig. 5 may according to an embodiment comprise apparatus 500. Apparatus 500 comprises a non-volatile memory 520, a data processing device 510 and a read/write memory 550. Non-volatile memory 520 has a first memory portion 530 wherein a computer program, such as an operating system, is stored for controlling the function of apparatus 500. Further, apparatus 500 comprises a bus controller, a serial communication port, l/O-means, an A/D-converter, a time date entry and transmission unit, an event counter and an interrupt controller (not shown). Non-volatile memory 520 also has a second memory portion 540.

A computer program P is provided comprising routines for facilitating steering of a vehicle during driving along a road according to an embodiment of the present invention. The program P comprises routines for determining the vehicle speed. The program P comprises routines for determining the curvature of the road. The program P comprises routines for determining a required yaw rate for the vehicle based upon the thus determined vehicle speed and curvature of the road. The program P comprises routines for determining 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 torque and yaw rate of the vehicle. The program P comprises routines for compensating the steering torque based upon said determined curvature compensation torque. The program P comprises routines for detecting the yaw rate of the vehicle. The program P comprises routines for modelling the yaw rate of the vehicle, the modelled yaw rate being based upon the steering torque of the vehicle. The modelled yaw rate is according to a variant obtained via a transfer function. The program P comprises routines for comparing the detected and modelled yaw rate. The program P comprises routines for filtering the result of said comparison between the detected and modelled yaw rate so as to avoid influence of rapid changes. The program P comprises routines for determining the influence of external forces on the yaw rate based on said comparison of detected and modelled yaw rate. The program P comprises routines for determining an external force compensation torque for compensating the steering torque of the vehicle based upon the determined influence of external forces on the yaw rate and said gain function determining. 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 gain function is obtained via said transfer function. Said gain function comprises a static gain. The program P comprises routines for compensating the steering torque based upon said determined external force compensation torque. The program P comprises routines for compensating the steering torque based upon said determined external force compensation torque. The program P comprises routines for determining a compensation torque based upon said determined curvature compensation torque and said determined external force compensation torque. The program P comprises routines for compensating the steering torque based upon said determined compensation torque. The computer program 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. When it is stated that data processing device 510 performs a certain function it should be understood that data processing device 510 performs a certain part of the program which is stored in separate memory 560, or a certain part of the program which is stored in read/write memory 550.

Data processing device 510 may communicate with a data communications port 599 by means of a data bus 515. Non-volatile memory 520 is adapted for communication with data processing device 510 via a data bus 512. Separate memory 560 is adapted for communication with data processing device 510 via a data bus 511. Read/write memory 550 is adapted for communication with data processing device 510 via a data bus 514. To the data communications port 599 e.g. the links connected to the control units 100 may be connected.

When data is received on data port 599 it is temporarily stored in second memory portion 540. When the received input data has been temporarily stored, data processing device 510 is set up to perform execution of code in a manner described above. The signals received on data port 599 can be used by apparatus 500 for determining the vehicle speed. The signals received on data port 599 can be used by apparatus 500 for determining the curvature of the road. The signals received on data port 599 can be used by apparatus 500 for determining a required yaw rate for the vehicle based upon the thus determined vehicle speed and curvature of the road. The signals received on data port 599 can be used by apparatus 500 for determining 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 torque and yaw rate of the vehicle.

The signals received on data port 599 can be used by apparatus 500 for compensating the steering torque based upon said determined curvature compensation torque. The signals received on data port 599 can be used by apparatus 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 of the vehicle, the modelled yaw rate being based upon the steering torque of the vehicle. The modelled yaw rate is according to a variant obtained via a transfer function. The signals received on data port 599 can be used by apparatus 500 for comparing the detected and modelled yaw rate. The signals received on data port 599 can be used by apparatus 500 for filtering the result of said comparison between the detected and modelled yaw rate so as to avoid influence of rapid changes. The signals received on data port 599 can be used by apparatus 500 for determining the influence of external forces on the yaw rate based on said comparison of detected and modelled yaw rate and said gain function determining. The signals received on data port 599 can be used by apparatus 500 for determining an external force compensation torque for compensating the steering torque of the vehicle based upon the determined influence of external forces on the yaw rate. 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 gain function is obtained via said transfer function. Said gain function comprises a static gain. The signals received on data port 599 can be used by apparatus 500 for compensating the steering torque based upon said determined external force compensation torque. The signals received on data port 599 can be used by apparatus 500 for determining a compensation torque based upon said determined curvature compensation torque and said determined external force compensation torque. The signals received on data port 599 can be used by apparatus 500 for compensating the steering torque based upon said determined compensation torque.

Parts of the methods described herein can be performed by apparatus 500 by means of data processing device 510 running the program stored in separate memory 560 or read/write memory 550. When apparatus 500 runs the program, parts of the methods described herein are executed.

The foregoing description of the preferred embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated.

Claims

1. A method for facilitating steering of a vehicle (1) during driving along a road (R),: comprising: - determining the vehicle speed; - determining the curvature of the road; - determining a required yaw rate for the vehicle based upon the thus determined vehicle speed and curvature of the road; and, - based upon said determined required yaw rate and a gain function relating to steering torque and yaw rate of the vehicle determining a curvature compensation torque for compensating the steering torque of the vehicle due to influence of curvature characterized by the steps of - detecting (S1) the yaw rate of the vehicle; - modelling (S2) the yaw rate of the vehicle based upon the steering torque of the vehicle; - comparing (S3) the detected and modelled yaw rate; - determining (S4) the influence of external forces on the yaw rate based on said comparison of detected and modelled yaw rate, said external 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 of external forces on the yaw rate and said gain function determining (S5) an external force compensation torque for compensating the steering torque of the vehicle due to influence of external forces.

2. A method according to claim 1, further comprising the step of determining a compensation torque based upon said determined curvature compensation torque and said determined external force compensation torque; and compensating the steering torque based upon said determined compensation torque.

3. A method according to any of claims 1-2, wherein the modelled yaw rate is obtained via a transfer function (G(z)).

4. A method according to claim 3, wherein said gain function is obtained via said transfer function (G(z)).

5. A method according to any preceding claims, wherein said gain function comprises a static gain.

6. A system (I; II; III) for facilitating steering of a vehicle (1) during driving along a road (R), comprising means (112; 212; 312) for determining the vehicle speed; means (114; 214; 314) for determining the curvature of the road; means (120; 220; 320) for determining a required yaw rate for the vehicle based upon the thus determined vehicle speed and curvature of the road; and means (130; 230; 330) for determining 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 torque and yaw rate of the vehicle characterized by means (144) for detecting the yaw rate of the vehicle; means (150; 350) for modelling the yaw rate 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 said comparison of detected and modelled yaw rate, said external 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 means (180; 380) for determining an external force compensation torque for compensating the steering torque of the vehicle due to influence of external forces based upon the determined influence of external forces on the yaw rate and said gain function,

7. A system according to claim 6, further comprising means (192; 392) for determining a compensation torque based upon said determined curvature compensation torque and said determined external force compensation torque; and means (194) for compensating the steering torque based upon said determined compensation torque.

8. A system according to any of claims 6-7, wherein the modelled yaw rate is obtained via a transfer function (G(z)).

9. A system according to claim 8, wherein said gain function is obtained via said transfer function (G(z)).

10. A system according to any preceding claims, wherein said gain function comprises a static gain.

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

12. A computer program (P) for facilitating steering of a vehicle during driving along 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 control unit to perform the steps according to claim 1-5.

13. A computer program product comprising a digital storage medium storing the computer program according to claim 12.