SE1550791A1 - A method and a system for steering a vehicle - Google Patents

Abstract

The invention relates to a method for steering a vehicle (100) comprising a front axle (FA) and a rear axle (RA2), wheels being arranged for steering said vehicle (100) being provided for said front axle (FA) and said rear axle (RA2), comprising the steps of: - controlling (s401) the steering action of said rear axle wheels (RW12, RW22) based upon a steering action exerted by said front axle wheels (FW1, FW2); and - determining (s401) a function (Fl) according to which the steering action is performed by means of said rear axle wheels (RW12, RW22), said function (Fl) comprising three different portions, namely a first, a second and a third portion, said portions corresponding to three different intervals of the steering action of the front axle wheels (FW1, FW2).The invention relates also to a computer programme product comprising program code (P) for a computer (200; 210; 500) for implementing a method according to the invention. The invention relates also to a system for steering a vehicle (100) comprising a front axle and a rear axle and a vehicle (100) equipped with the system.Figure 2 for publication

Description

A method and a system for steering a vehicle TECHNICAL FIELD The present inventíon relates to a method for steering a vehicle comprising a front axle anda rear axle. More particularly, the invention relates to a method for steering a vehiclecomprising a front axle and a rear tag axle. The inventíon relates also to a computer programproduct comprising program code for a computer for implementing a method according tothe invention. lt relates also to a system for steering a vehicle comprising a front axle and a rear axle and a vehicle being equipped with the system.

BACKG ROUND Some vehicles of today are provided with a so called tag axle wheel steering functionality.Said vehicles may be a truck or lorry. Such vehicles may be arranged with steerable frontwheels being provided at a front wheel axle. Hereby an operator may control steering of saidfront wheels during propulsion by means of steering wheels. Said vehicles are provided witha drive axle for propelling said vehicle by means of thereto associated drive wheels. Said tag axle is a support axle being provided with steerable wheels.

One common hydraulic steering configuration is hereby provided for controlling steering ofboth said front wheels and said tag axle wheels. This configuration is rather bulky and requires fluid pipes to each of said front axle and said tag axle.

Said tag axle wheel steering functionality is today performed based on a current steeringwheel angle but is not providing sufficient or desired aid for manoeuvring said vehicle in alltraffic situations. The tag axle wheel steering functionality is today limited in various ways and also static to its nature.

Said tag axle wheel steering functionality is today sub-optimized e.g. paying regard to the number of optimization parameters.

US6763906 refers to a power steering system for rear axle wheels of a vehicle.

SUMMARY OF THE INVENTION An object of the present invention is to propose a novel and advantageous method for steering a vehicle.

Another object of the invention is to propose a novel and advantageous system and a novel and advantageous computer program for steering a vehicle.

An object of the present invention is to propose a novel and advantageous method for providing a more versatile steering of a vehicle.

Another object of the invention is to propose a novel and advantageous system and a novel and advantageous computer program for providing a more versatile steering of a vehicle.

Yet another object of the invention is to propose a method, a system and a computer program for achieving a user friendly and reliable steering of a vehicle.

Yet another object of the invention is to propose a method, a system and a computer program for achieving a robust and cost-effective steering of a vehicle.

Yet another object of the invention is to propose an alternative method, an alternative system and an alternative computer program for steering of a vehicle.

Some of these objects are achieved with a method for steering a vehicle according to claim1. Other objects are achieved with a system according to claim 13. Advantageousembodiments are depicted in the dependent claims. Substantially the same advantages ofmethod steps of the innovative method hold true for corresponding means of the innovative system.

According to an aspect of the invention there is provided a method for steering a vehiclecomprising a front axle and a rear axle, wheels being arranged for steering said vehicle being provided for said front axle and said rear axle, comprising the steps of: - controlling the steering action of said rear axle wheels based upon a steering action exerted by said front axle wheels; - determining a function according to which the steering action is performed by means ofsaid rear axle wheels, said function comprising three different portions, namely a first, asecond and a third portion, said portions corresponding to three different intervals of the steering action of the front axle wheels.

Hereby is provided a method for steering a vehicle which achieves different advantageswithin the different portions. Hereby said method is optimized regarding a plurality of parameters. Hereby an improved method for steering a vehicle is provided.

Hereby is achieved a more versatile method for steering the vehicle. Hereby it is providedimproved manoeuvrability of the vehicle during reverse propulsion as well as forwardpropulsion. An operator ofthe vehicle may in a user friendly way drive the vehicle in arearward direction more safely and smoothly according to an embodiment of the invention.For example a process of parallel parking in a rearward direction may be significantly facilitated.

According to one embodiment two separate steering configurations are provided, one forcontrolling steering of wheels of one or more rear axles of the vehicle and one for controllingsteering of wheels of a front axle of the vehicle. These steering configurations may forexample be an electro-mechanical steering configuration or a hydraulic steering configuration.

According to one embodiment an operator of the vehicle may manually activate a steeringfunctionality according to the invention for use during reverse propulsion of the vehicleand/or during forward propulsion of the vehicle. According to one em bodiment activation ofsaid innovative steering functionality may be performed automatically when said vehicle is operated.The method may comprise the step of: - controlling the steering action exerted by means of said rear axle wheels according to said determined function. Hereby an operator does not have to turn a steering wheel of the vehicle as many degrees, or turns, to achieve a desired steering of the vehicle during reverse propulsion.The method may comprise the step of: - determining said function based upon at least one of vehicle speed, front axle wheelsteering action speed, vehicle mass, surrounding configuration and vehicle axleconfiguration. Hereby an optimal function may be determined, which further enhance and simplifies steering of the vehicle during operation.The method may comprise the step of: - determining a first portion of said function such that it corresponds to steering action ofsaid front axle wheels from no steering action up to a first steering action value, the steeringaction of the rear axle wheels being su bstantially zero during said first portion of saidfunction. Hereby a reduced wear of a steering configuration is reduced. Said steeringconfiguration may comprise a hydraulic pump device, a hydraulic cylinder for controllingsteering of vehicle wheel and force transmitting means for affecting wheels being provided at opposite ends of a rear wheel axle, such as a tag axle.

Hereby is provided a so called dead band area where no steering of rear axle wheels isperformed. Said dead band area may be a static dead band area which is not adapted based on e.g. vehicle speed.

Advantageously potential variances of a steering geometry of the vehicle dependent onvarious carried loads are hereby managed effectively. Steering of said rear axle wheels isthus not activated unintentionally in case a steering wheel is not centred due to heavy loadof the vehicle, even if front steering wheels are presented in line with a longítudinal axis of the vehicle.

Advantageously there is no need to adapt the innovative method for steering on the basis ofa clutch position state. Advantageously there is no need to adapt the innovative method forsteering on the basis of if a gearbox of a transmission of the vehicle is set to a neutral position or not.

The method may comprise the step of: - determining a second portion of said function such that it corresponds to steering action ofsaid front axle wheels from said first steering action value to a second steering action value,the steering action of the rear axle wheels increases preferably continuously with increasingsteering action of said front axle wheels. Hereby a reduced tire wear of the wheels of thevehicle is advantageously achieved. Said second portion of said function may be determined on the basis of so called Ackermann control.The method may comprise the step of: - determining a third portion of said function such that it corresponds to steering action ofsaid front axle wheels from said second steering action value to a third steering action value,the steering action of the rear axle wheels increases with increasing steering action of saidfront axle wheels. Hereby a reduced clearance circle of the vehicle during operation corresponding to said third portion of said function.The method may comprise the step of: - determining a third portion of said function such that the steering action of the rear axlewheels increases more rapidly than during said second portion of said function. Hereby a reduced clearance circle of the vehicle during operation is achieved.The method may comprise the step of: - determining a third portion of said function such that the steering action of the rear axlewheels comprises a maximum allowable steering action value. Hereby a reduced clearance circle of the vehicle during operation is achieved.The method may comprise the step of: - determining said second portion of said function such that the steering action of said rearaxle wheels is initiated smoothly. This provides a comfortable steering method according toan aspect of the invention which naturally is experienced in a positive way of the operator of the vehicle.

The method may comprise the step of: - determining said function for said third portion of said function such that it is adapted tosaid second portion of said function. This provides a comfortable steering method accordingto an aspect of the invention which naturally is experienced in a positive way of the operator of the vehicle.

The method may comprise the steps of: - determining if said vehicle is set for reverse propulsion or forward propulsion; and - determining said function on the basis of the direction of propulsion. Hereby a more versatile method for steering is provided.

The method may comprise the step of: - determining said function such that said first portion corresponds to an interval of zerosteering action of said front axle wheels. According to this em bodiment steering of said rearaxle wheels may be performed during certain steering manoeuvres such as during and S-turnor when entering and leaving a roundabout. Hereby is provided a flexible and user-friendly method for steering a vehicle.

According to an aspect of the invention there is provided a system for steering a vehiclecomprising a front axle and a rear axle, wheels being arranged for steering said vehicle being provided for said front axle and said rear axle, comprising: - means for controlling the steering action of said rear axle wheels based upon a steering action exerted by said front axle wheels; - means for determining a function according to which the steering action is performed bymeans of said rear axle wheels, said function comprising three different portions, namely afirst, a second and a third portion, said portions corresponding to three different intervals of the steering action of the front axle wheels.

The system may comprise: - means for controlling the steering action exerted by means of said rear axle wheels according to said determined function.

The system may comprise: - means for determining said function based upon at least one of vehicle speed, front axlewheel steering action speed, vehicle mass, surrounding configuration and vehicle axle configuration.The system may comprise: - means for determining a first portion of said function such that it corresponds to steeringaction of said front axle wheels from no steering action up to a first steering action value,the steering action of the rear axle wheels being substantially zero during said first portion of said function.The system may comprise: - means for determining a second portion of said function such that it corresponds tosteering action of said front axle wheels from said first steering action value to a secondsteering action value, the steering action of the rear axle wheels increases preferably continuously with increasing steering action of said front axle wheels.The system may comprise: - means for determining a third portion of said function such that it corresponds to steeringaction of said front axle wheels from said second steering action value to a third steeringaction value, the steering action of the rear axle wheels increases with increasing steering action of said front axle wheels.The system may comprise: - means for determining a third portion of said function such that the steering action of the rear axle wheels increases more rapidly than during said second portion of said function.The system may comprise: - means for determining a third portion of said function such that the steering action of the rear axle wheels comprises a maximum allowable steering action value.

The system may comprise: - means for determining said second portion of said function such that the steering action of said rear axle wheels is initiated smoothly.

The system may comprise: - means for determining said function for said third portion of said function such that it isadapted to said second portion of said function. Hereby a lower end point of said thirdportion of said function is set to correspond a higher end point of said second portion of saidfunction. This advantageously provides a smooth transition between said second portionand said third portion as well as a smooth transition between said second portion and said third portion.

The system may comprise: - means for determining if said vehicle is set for reverse propulsion or forward propulsion; and - means for determining said function on the basis ofthe direction of propulsion.

The system may comprise: - means for determining said function such that said first portion corresponds to an interval of zero steering action of said front axle wheels.

According to an aspect of the invention there is provided a vehicle comprising the innovative system. The vehicle may be any from among a truck, bus or passenger car.

According to an aspect of the invention there is provided a computer program for steering avehicle comprising a front axle and a rear axle, wherein said computer program comprisesprogram code for causing an electronic control unit or a computer connected to theelectronic control unit to perform the steps according to anyone of the claims 1-12, when run on said electronic control unit or said computer.

According to an aspect of the invention there is provided a computer program for steering avehicle comprising a front axle and a rear axle, wherein said computer program comprisesprogram code stored on a computer-readable medium for causing an electronic control unitor a computer connected to the electronic control unit to perform the steps according to anyone of the claims 1-12.

According to an aspect of the invention there is provided a computer program for steering avehicle comprising a front axle and a rear axle, wherein said computer program comprisesprogram code stored on a computer-readable medium for causing an electronic control unitor a computer connected to the electronic control unit to perform the steps according to anyone of the claims 1-12, when run on said electronic control unit or said computer.

According to an aspect of the invention there is provided a computer program productcontaining a program code stored on a computer-readable medium for performing methodsteps according to anyone of claims 1-12, when said computer program is run on an electronic control unit or a computer connected to the electronic control unit.

According to an aspect of the invention there is provided a computer program productcontaining a program code stored non-volatile on a computer-readable medium forperforming method steps according to anyone of claims 1-12, when said computer program is run on an electronic control unit or a computer connected to the electronic control unit.

Further objects, advantages and novel features of the present invention will becomeapparent to one skilled in the art from the following details, and also by putting theinvention into practice. Whereas the invention is described below, it should be noted that itis not confined to the specific details described. One skilled in the art having access to theteachings herein will recognise further applications, modifications and incorporations in other fields, which are within the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS For fuller understanding of the present invention and its further objects and advantages, thedetailed description set out below should be read in conjunction with the accompanyingdrawings, in which the same reference notatíons denote similar items in the various diagrams, and in which: Figure 1 schematically illustrates a vehicle according to an embodiment of the invention;Figure 2 schematically illustrates a subsystem for the vehicle depicted in Figure 1, accordingto an embodiment of the invention; Figure 3 schematically illustrates a diagram presenting a rear axle wheel angle as a functionof a steering wheel angle, according to an embodiment of the invention; Figure 4a is a schematic flowchart of a method according to an embodiment of theinvention; Figure 4b is a more detailed schematic flowchart of a method according to an embodimentof the invention; and Figure 5 schematically illustrates a computer according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS Figure 1 depicts a side view of a vehicle 100. The exemplified vehicle 100 is hereby a tractorunit to which a trailer unit (not shown) may be connected. The vehicle may be a heavy vehicle, e.g. a truck or a bus. lt may alternatively be a car.

Herein said vehicle is provided with a front wheel axle FA, a driving first rear axle RA1 and asecond rear axle RA2. Said first rear axle RA1 is hereby a driving axle being arranged forpropelling said vehicle 100. Said second rear axle RA2 is a steerable tag axle of the vehicle 100. lt should be noted that the inventive system for steering a vehicle is applicable to variousvehicles having a front axle and at least one rear axle, wheels being arranged for steeringsaid vehicle being provided for said front axle and said at least one rear axle, such as e.g. amining machine, tractor, dumper, wheel loader, platform comprising an industrial robot, forest machine, earth mover, road construction vehicle or emergency vehicle. The vehicle 11 100 may according to an example be an autonomous vehicle. The inventive method isapplicable to vehicles comprising a front axle and at least one rear axle, wheels beingarranged for steering said vehicle being provided for said front axle and said at least one rear axle. Said at least one rear axle may be two rear axles, each having steerable wheels.

The term "link" refers herein to a communication link which may be a physical connectionsuch as an opto-electronic communication line, or a non-physical connection such as a wireless connection, e.g. a radio link or microwave link.

The term ”steering action” refers herein to a steering action of wheels of said front axle FAand steering action of steerable rear wheels of a rear axle, such as said tag axle RA2. Thesteering actions of the vehicle 100 correspond to wheel angles of said steerable front wheelsand said steerable rear wheels, respectively. Even though the invention herein is depictedwith reference to a vehicle comprising a front axle with steera ble wheels, a driving rear axlewith non-steerable wheels and a rear tag axle with steera ble wheels the invention isapplicable to various vehicle wheel axle configurations. The vehicle may be arranged withany suitable wheel axle configuration comprising two or more rear axles having steerablewheels. Hereby controlling the steering action of wheels of each of said rear axles may bebased upon a steering action exerted by said front axle wheels. Hereby a respective functionaccording to which the steering action is performed by means of wheels of each of said rearaxles is determined, said functions may provide a steering action during reverse propulsiondifferent from the steering action provided by means of said rear axle wheels when saidvehicle is set for forward propulsion. Thus, steerable wheels of each of said rear axles maybe controlled mutually different and/or independently according to each respective determined function when the vehicle 100 is determined to be set for reverse propulsion.

Figure 2 schematically illustrates a subsystem of the vehicle 100. A framework FW isarranged to hold a number of wheel axles. According to this example embodiment saidvehicle 100 is arranged with three wheel axles. A front wheel axle FA is arranged with a rightfront wheel FW1 and a left front wheel FW2. A first rear wheel axle RA1 is arranged with a right rear wheel RW11 and a left rear wheel RWl2. Said first rear wheel axle RA1 is arranged 12 to propel said vehicle 100 by means of said right rear wheel RW11 and said left rear wheelRW12. An engine (not shown) is arranged to provide torque to said first rear wheel axle RA1via a transmission (not shown) for propelling said vehicle 100. Said right rear wheel RW11and said left rear wheel RW12 are according to this example not steerable. A second rearwheel axle RA2 is arranged with a right rear wheel RW2l and a left rear wheel RW22. Saidright rear wheel RW21 and said left rear wheel RW22 are steerable. Said second rear wheel axle RA2 is hereby a so called tag axle.

A first sensor configuration 230 is arranged for communication with a first electronic controlunit 200 via a link L230. Said first sensor configuration 230 is arranged to continuously orintermittently determine a steering action performed by an operator of the vehicle 100. Saidfirst sensor configuration 230 is arranged to determine a front wheel angle oil. Said frontwheel angle oil is defined relative a longitudinal axle of said vehicle 100, corresponding to astraight propulsion direction of said vehicle 100 (forward or reverse). Said front wheel angleal is present at said right front wheel FW1 and said left front wheel FW2. Herein said frontwheel angle oil is only illustrated at said left front wheel FW2 for sake of clarity. Said firstsensor configuration 230 may comprise a front wheel angle sensor. Said first sensorconfiguration 230 may be arranged at one of said right front wheel FW1 and said left frontwheel FW2, or at both of said right front wheel FW1 and said left front wheel FW2. Said firstsensor configuration 230 is arranged to continuously or intermittently send signals S230comprising information about said detected front wheel angle otl to the first control unit 200 via said link L230.

A second sensor configuration 240 is arranged for communication with the first electroniccontrol unit 200 via a link L240. Said second sensor configuration 240 is arranged tocontinuously or intermittently determine a steering action performed by the operator of thevehicle 100. Said second sensor configuration 240 is arranged to determine a steering wheelangle 012. Said steering wheel angle oi2 is defined relative a reference steering wheel anglecorresponding to a straight propulsion direction of said vehicle 100. Said steering wheelangle 0:2 corresponds to said front wheel angle otl being present at said right front wheelFW1 and said left front wheel FW2. Said second sensor configuration 240 may comprise asteering wheel angle sensor. Said first sensor configuration 230 may be arranged at a steering wheel arrangement (not shown) of the vehicle 100. Said second sensor 13 configuration 240 is arranged to continuously or intermittently send signals S240 comprisinginformation about said detected steering wheel angle 012 to the first control unit 200 via said link L240.

Said front wheel angle otl and said steering wheel angle oi2 are two different representations of a steering action performed by the operator of the vehicle 100. ln case said vehicle 100 is an autonomous vehicle said steering actions are not performedmanually, but automatically. Hereby said front wheel angle oil and said steering wheel angleoL2 are two different representations of a steering action performed autonomously by thevehicle 100. Such steering actions may be controlled by e.g. said first control unit 200. lt should be noted that the inventive method is applicable on an autonomous vehicle.

Said first control unit 200 is arranged to determine if said vehicle 100 is set for forwardpropulsion or reverse propulsion. This may be performed in any suitable way. According toan example said first control unit 200 is arranged to determine a prevailing gear state of agearbox of a transmission of the vehicle 100. According to an example said first control unit200 is arranged to determine if an operator manually has requested a particular gear state ofsaid gearbox. According to one example said first control unit 200 is arranged to determine apropulsion direction of said vehicle on the basis of at least one speed sensor of said vehicle, so as to determine if said vehicle is propelled in a forward direction or a reverse direction.

A second control unit 210 is arranged for communication with the first control unit 200 via alink L210. Said second control unit 210 is arranged to communicate with said first controlunit 200 by means of signals S210. lt may be adapted to conducting the innovative methodsteps according to the invention. The second control unit 210 may be arranged to performthe inventive method steps according to the invention. lt may be used to cross-load softwareto the first control unit 200, particularly software for conducting the innovative method. ltmay alternatively be arra nged for communication with the first control unit 200 via aninternal network on board the vehicle 100. lt may be adapted to performing substantiallythe same functions as the first control unit 200, such as controlling the steering actionexerted by means of said second rear axle wheels according to a determined function. This isdepicted in greater detail below. The innovative method may be conducted by the first control unit 200 or the second control unit 210, or by both of them. 14 The second control unit 210 is arranged to control steering of said second rear axle wheelsRW21 and RW22 according to an aspect of the invention. The second control unit 210 isarranged to continuously send control signals S250 to a steering configuration 250 via a linkL250. Said steering configuration 250 is arranged to control steering of said second rear axlewheels RW21 and RW22 based on said control signals S250. Said steering arrangement 250may be any suitable steering arrangement. Said steering arrangement 250 may e.g. be an electro-mechanical steering arrangement or a hydraulic steering arrangement.

Said second rear axle wheels RW21 and RW22 are hereby controlled by means of saidsecond control unit 210 so as to present a desired rear axle wheel angle oL3. Said rear axlewheel angle oL3 is defined relative a longitudinal axle of said vehicle 100, corresponding to astraight propulsion direction of said vehicle 100 (forward or reverse). Said rear axle wheelangle oL3 is present at said right rear axle wheel RW21 and said left rear axle wheel RW22.Herein said rear axle wheel angle oi3 is only illustrated at said left rear axle wheel RW22 for sake of clarity.

With reference to Figure 3 there is schematically illustrated a diagram according to an embodiment of the invention.

Hereby is presented a function Fl depicting the relation between a rear axle wheel angle 0:3and a front wheel angle oil for a reverse propulsion and/or a forward propulsion of thevehicle 100. The rear axle wheel angle oi3 is presented in degrees [Deg]. The front wheelangle otl is presented in degrees [Deg]. lt should be noted that the herein depicted steeringwheel angle 0:2 corresponds to said front wheel angle al and the function F1 of the diagram of Figure 3 could thus alternatively be presented for the rear axle wheel angle oL3 and the steering wheel angle (12 for reverse propulsion and/or forward propulsion of the vehicle 100.

Herein is with other words said function F1 presented as a relation between said rear wheel angle 013 and a steering action of said vehicle 100.

Said function Fl may be a predetermined function.

Said function Fl is presented having two sections, one referring to turning the front wheelsto the right relative a longitudinal axis of the vehicle 100 and one referring to turning thefront wheels to the left relative a longitudinal axis of the vehicle 100. Said two sections of said function Fl are substantially symmetrical.

The function Fl comprises three different portions for each turning direction of said vehicle100. Each of said three portions is thus provided for right turns of said steering wheel and left turns of said steering wheel, respectively.

According to this embodiment a first portion of said function Fl is equal to zero within aninterval defined by [0, oill] (and [-oLll, 0] correspondingly). Hereby a so called dead bandarea is provided. Said dead band area [-cx1l, all] may be defined as [10, -l0], [20, -20], [30, -301 or any suitable interval.

A second portion of said function Fl is provided. Said second portion is defined as [oL1l, 0:12](and [-oLll, -al2] correspondingly). Said second portion of the function Fl is according to anembodiment of the invention the greatest portion of the three provided portions. Saidsecond portion of the function Fl may be defined as [l0, 720], [20, 1080], [90, 2160] or anysuitable interval. A first part (relating to lower values of oil) of said second portion of saidfunction Fl may be smoothly curved for improved vehicle operator comfort. A second partof said second portion of said function Fl may be a linear function presenting any suitable slope.

A third portion of said function Fl is provided. Said third portion is defined as [oL12, 0113](and [-cxl2, -cxl3] correspondingly). Said third portion of the function Fl may be defined as[720, 1080], [l080, 2160], [2l60, 2520] or any suitable interval. Said third portion of saidfunction Fl may be a linear function presenting any suitable slope. A transition between saidsecond portion and said third portion, or vice versa, should be smooth for maintained operator comfort. 16 Figure 4a schematically illustrates a flow chart of a method for steering a vehicle 100comprising a front axle FA and a rear axle RA2, wheels being arranged for steering saidvehicle 100 being provided for said front axle FA and said rear axle RA2. The method comprises the method step s401. The method step s40l comprises the steps of: - controlling the steering action (13 of said rear axle wheels RW21 and RW22 based upon a steering action (al or (12) exerted by said front axle wheels FW1 and FW2; and - determining a function Fl according to which the steering action ot3 is performed by meansof said rear axle wheels RW21 and RW22, said function Fl comprising three differentportions, namely a first, a second and a third portion, said portions corresponding to three different intervals of the steering action Fl of the front axle wheels FW1 and FW2.

After the method step s401 the method is returned or is ended.

Figure 4b schematically illustrates a flow chart of a method for steering a vehicle 100comprising a front axle FA and a rear axle RA2, wheels being arranged for steering saidvehicle l00 being provided for said front axle FA and said rear axle RA2. The method comprises the method step s4l0.

The method step s4l0 comprises the step of determining if said vehicle l00 is set for reversepropulsion or forward propulsion. This may be performed automatically by means of saidfirst control unit 200. Alternatively an operator of the vehicle 100 may manually provideinformation about an active propulsion state by any suitable means to the first control unit 200.

Herein said function Fl may be determined on the basis of the direction of propulsion. ltshould be noted that said function Fl may be determined on the basis of determined setpropulsion state of the vehicle 100. The function Fl determined in a case whereby saidvehicle l00 is set for forward propulsion may thus be different compared to a case whereby said vehicle is set for reverse propulsion.

The method step s4l0 may be performed by means of said first control unit 200. After the method step s4l0 a subsequent method step s420 is performed. 17 The method step s420 comprises the step of determining a first portion of a function Flaccording to which the steering action 013 may be performed by means of said rear axle wheels RW21 and RW22.

The method step s420 may comprise the step of determining said first portion of saidfunction Fl such that it corresponds to steering action (01l or 012) of said front axle wheelsFW1 and FW2 from no steering action (o1l=0 or 012=0) up to a first steering action value -01llor 01ll, the steering action of the rear axle wheels RW21 and RW22 being substantially zeroduring said first portion of said function Fl. Hereby a so called dead band area is providedwithin a predetermined steering action value interval (-01ll to 0111). Hereby no steering ofsaid rear axle wheels is performed for any steering action values within said interval. This advantageously reduces wear of e.g. said steering configuration 250.The method step s420 may be performed by means of said first control unit 200.

After the method step s420 a subsequent method step s430 is performed.

The method step s430 comprises the step of determining a second portion of a function Flaccording to which the steering action 013 may be performed by means of said rear axle wheels RW21 and RW22.

The method step s430 may comprise the step of determining a second portion of saidfunction Fl such that it corresponds to steering action of said front axle wheels FW1 andFW2 from said first steering action value (-0111 or 0111) to a second steering action value(-0112 or 0112), the steering action 013 of the rear axle wheels RW21 and RW22 increasespreferably continuously with increasing steering action 011 or 012 of said front axle wheels FW1 and FW2.

The method step s430 may comprise the step of determining said second portion of saidfunction Fl such that the steering action 013 of said rear axle wheels RW21 and RW22 is initiated smoothly.

The method step s430 may be performed by means of said first control unit 200. 18 After the method step s430 a subsequent method step s440 is performed.

The method step s440 comprises the step of determining a third portion of a function Flaccording to which the steering action 013 may be performed by means of said rear axle wheels RW21 and RW22.

The method step s440 may comprise the step of determining a third portion of said functionFl such that it corresponds to steering action 011 or 012 of said front axle wheels FW1 andFW2 from said second steering action value (-0112 or 0112) to a third steering action value(-0113 or 0113), the steering action 013 of the rear axle wheels RW21 and RW22 increases withincreasing steering action 011 or 012 of said front axle wheels FW1 and FW2. Hereby said thirdportion of said function Fl may be determined such that the steering action 013 of the rearaxle wheels RW21 and RW22 increases more rapidly with increasing steering action 011 or 012 of said front axle wheels FW1 and FW2 than during said second portion of said function Fl.

The method step s440 may comprise the step of determining said third portion of saidfunction Fl such that the steering action 013 of the rear axle wheels RW21 and RW22 comprises a maximum allowa ble steering action value -013max or 013max.

The method step s440 may comprise the step of determining said function Fl for said thirdportion of said function Fl such that it is adapted to said second portion of said function.Hereby a smooth transition between said second portion of said function Fl and said thirdportion of said function Fl is provided, either going from said second portion to said third portion or going from said third portion to said second portion.

According to an embodiment of the invention said at least one of said three portions of saidfunction Fl may be determined based upon at least one of vehicle speed, front axle wheelsteering action speed, vehicle mass, surrounding configuration and vehicle axle configuration.

Hereby said function Fl may be determined so as to provide a lesser slope of said functionFl for relatively high vehicle speeds. Hereby said function Fl may be determined so as to provide a greater slope of said function Fl for relatively low vehicle speeds. 19 Hereby said function Fl may be determined so as to provide a lesser slope of said functionFl for relatively high front axle wheel steering action speeds (time derivative of steeringwheel angle or time derivative of front wheel angle). Hereby said function Fl may bedetermined so as to provide a steeper slope of said function Fl for relatively low front axle wheel steering action speeds.

Hereby said function Fl may be determined so as to provide a lesser slope of said functionFl for relatively high vehicle masses. Hereby said function Fl may be determined so as to provide a steeper slope of said function Fl for relatively small vehicle masses.

Hereby said function Fl may be determined so as to provide a lesser slope of said functionFl for relatively long vehicles having a vehicle axle configuration wherein said front axle FA isrelatively remotely arranged from said rear axle RA2. Hereby said function Fl may bedetermined so as to provide a steeper slope of said function Fl for relatively short vehicleshaving a vehicle axle configuration wherein said front axle FA is relatively closely arranged from said rear axle RA2.

Hereby said function Fl may be determined on the basis of a surrounding configuration. Thevehicle 100 may be arranged with sensors, such as a video camera or radar unit, so as todetermine a surrounding configuration of the vehicle. Hereby said first control unit may bearranged to determine said function Fl on the basis of detected movable or fixed objects in the surrounding of the vehicle.The method step s440 may be performed by means of said first control unit 200.

After the method step s440 a subsequent method step s45O is performed.

The method step s45O comprises the step of controlling the steering action oi3 exerted bymeans of said rear axle wheels RW2l and RW22 according to said determined function Fl.

The method step s45O may be performed by means of said second control unit 200.

After the method step s45O the method is returned or ended.

Figure 5 is a diagram of one version of a device 500. The control units 200 and 210 describedwith reference to Figure 2 may in one version comprise the device 500. The device 500comprises a non-volatile memory 520, a data processing unit 510 and a read/write memory550. The non-volatile memory 520 has a first memory element 530 in which a computerprogram, e.g. an operating system, is stored for controlling the function of the device 500.The device 500 further comprises a bus controller, a serial communication port, I/O means,an A/D converter, a time and date input and transfer unit, an event counter and aninterruption controller (not depicted). The non-volatile memory 520 has also a second memory element 540.

There is provided a computer program P for steering a vehicle 100 comprising a front axle FAand a rear axle RA2, wheels being arranged for steering said vehicle 100 being provided forsaid front axle FA and said rear axle RA2.

The computer program P comprises routines for - controlling the steering action of said rear axle wheels based upon a steering action exerted by said front axle wheels; and - determining a function according to which the steering action is performed by means ofsaid rear axle wheels, said function comprising three different portions, namely a first, asecond and a third portion, said portions corresponding to three different intervals of the steering action of the front axle wheels.

The computer program P may comprise routines for controlling the steering action exerted by means of said rear axle wheels according to said determined function.

The computer program P may comprise routines for determining said function based uponat least one of vehicle speed, front axle wheel steering action speed, vehicle mass, surrounding configuration and vehicle axle configuration.

The computer program P may comprise routines for determining a first portion of saidfunction such that it corresponds to steering action of said front axle wheels from nosteering action up to a first steering action value, the steering action of the rear axle wheels being su bstantially zero during said first portion of said function. 21 The computer program P may comprise routines for determining a second portion of saidfunction such that it corresponds to steering action of said front axle wheels from said firststeering action value to a second steering action value, the steering action of the rear axlewheels increases preferably continuously with increasing steering action of said front axle wheels.

The computer program P may comprise routines for determining a third portion of saidfunction such that it corresponds to steering action of said front axle wheels from saidsecond steering action value to a third steering action value, the steering action of the rear axle wheels increases with increasing steering action of said front axle wheels.

The computer program P may comprise routines for determining a third portion of saidfunction such that the steering action of the rear axle wheels increases more rapidly than during said second portion of said function- The computer program P may comprise routines for determining a third portion of saidfunction such that the steering action of the rear axle wheels comprises a maximum allowable steering action value.

The computer program P may comprise routines for determining said second portion of said function such that the steering action of said rear axle wheels is initiated smoothly.

The computer program P may comprise routines for determining said function for said third portion of said function such that it is adapted to said second portion of said function.

The computer program P may comprise routines for determining if said vehicle is set forreverse propulsion or forward propulsion and determining said function on the basis of the direction of propulsion.

The computer program P may comprise routines for determining said function such that said first portion corresponds to an interval of zero steering action of said front axle wheels. 22 The program P may be stored in an executable form or in compressed form in a memory 560 and/or in a read/write memory 550.

Where it is stated that the data processing unit 510 performs a certain function, it meansthat it conducts a certain part of the program which is stored in the memory 560 or a certain part of the program which is stored in the read/write memory 550.

The data processing device 510 can communicate with a data port 599 via a data bus 515.The non-volatile memory 520 is intended for communication with the data processing unit510 via a data bus 512. The separate memory 560 is intended to communicate with the dataprocessing unit via a data bus 511. The read/write memory 550 is arranged to communicatewith the data processing unit 510 via a data bus 514. The links L210, L230, L240 and L250, for example, may be connected to the data port 599 (see Figure 2).

When data are received on the data port 599, they are stored temporarily in the secondmemory element 540. When input data received have been temporarily stored, the data processing unit 510 will be prepared to conduct code execution as described above.

Parts of the methods herein described may be conducted by the device 500 by means of thedata processing unit 510 which runs the program stored in the memory 560 or theread/write memory 550. When the device 500 runs the program, methods herein described are executed.

The foregoing description of the preferred em bodiments of the present invention isprovided for illustrative and descriptive purposes. lt is not intended to be exhaustive, nor tolimit the invention to the variants described. Many modifications and variations willobviously suggest themselves to one skilled in the art. The embodiments have been chosenand described in order to best explain the principles of the invention and their practicalapplications and thereby make it possible for one skilled in the art to understand theinvention for different embodiments and with the various modifications appropriate to the intended use.

Claims (27)

23 Claims

1. l. A method for steering a vehicle (100) comprising a front axle (FA) and a rear axle (RA2),wheels being arranged for steering said vehicle (100) being provided for said front axle (FA) and said rear axle (RA2), comprising the step of: - controlling (s40l) the steering action of said rear axle wheels (RW12, RW22) based upon a steering action exerted by said front axle wheels (FW1, FW2), characterized by the steps of: - determining (s40l) a function (Fl) according to which the steering action is performed bymeans of said rear axle wheels (RW12, RW22), said function (Fl) comprising three differentportions, namely a first, a second and a third portion, said portions corresponding to three different intervals of the steeríng action of the front axle wheels (FW1, FW2).

2. The method according to claim l, comprising the step of: - controlling the steering action exerted by means of said rear axle wheels according to said determined function (Fl).

3. The method according to claim l or 2, comprising the step of: - determining said function (Fl) based upon at least one of vehicle speed, front axle wheelsteering action speed, vehicle mass, surrounding configuration and vehicle axle configuration.

4. The method according to anyone of the claims 1-3, comprising the step of: - determining (s420) a first portion of said function (Fl) such that it corresponds to steeringaction of said front axle wheels (FW1, FW2) from no steering action up to a first steeringaction value, the steering action of the rear axle wheels (RW12, RW22) being substantially zero during said first portion of said function (Fl). 24

5. The method according to anyone of the claims 1-4, comprising the step of: - determining (5430) a second portion of said function (Fl) such that it corresponds tosteering action of said front axle wheels from said first steering action value to a secondsteering action value, the steering action of the rear axle wheels increases preferably continuously with increasing steering action of said front axle wheels.

6. The method according to anyone of the claims 1-5, comprising the step of: - determining (s440) a third portion of said function (Fl) such that it corresponds to steeringaction of said front axle wheels (FWl, FW2) from said second steering action value to a thirdsteering action value, the steering action of the rear axle wheels (RWl2, RW22) increases with increasing steering action of said front axle wheels (FWl, FW2).

7. The method according to claims 6, comprising the step of: - determining (s440) said third portion of said function (Fl) such that the steering action of the rear axle wheels increases more rapídly than during said second portion of said function.

8. The method according to claims 6 or 7, comprising the step of: - determining (s440) said third portion of said function (Fl) such that the steering action of the rear axle wheels (RWl2, RW22) comprises a maximum allowable steering action value.

9. The method according to anyone of the claims l-8, comprising the step of: - determining (5430) said second portion of said function (Fl) such that the steering action of said rear axle wheels (RWl2, RW22) is initiated smoothly.

10. The method according to anyone of the claims 1-9, comprising the step of: - determining (s440) said function (Fl) for said third portion of said function such that it is adapted to said second portion of said function (F1).

11. The method according to anyone of the claims 1-10, comprising the steps of:- determining if said vehicle (100) is set for reverse propulsion or forward propulsion; and - determining said function (F1) on the basis of the direction of propulsion.

12. The method according to anyone of the claims 1-11, comprising the step of: - determining said function (Fl) such that said first portion corresponds to an interval of zero steering action of said front axle wheels (FW1, FW2).

13. A system for steering a vehicle (100) comprising a front axle (FA) and a rear axle (RA2),wheels being arranged for steering said vehicle (100) being provided for said front axle (FA) and said rear axle (RA2), comprising: - means (200; 210; 500; 250) for controlling the steering action of said rear axle wheels(RW12, RW22) based upon a steering action exerted by said front axle wheels (FW1, FW2), characterized by: - means (200; 210; 500) for determining a function (F1) according to which the steeringaction is performed by means of said rear axle wheels (RW12, RW22), said function (F1)comprising three different portions, namely a first, a second and a third portion, saidportions corresponding to three different intervals of the steering action of the front axle wheels (FW1, FW2).

14. The system according to claim 13, comprising: 26 - means (200; 210; 500; 250) for controlling the steering action exerted by means of said rear axle wheels (RW12, RW22) according to said determined function (F1).

15. The system according to claim 13 or 14, comprising: - means (200; 210; 500) for determining said function (Fl) based upon at least one of vehiclespeed, front axle wheel steering action speed, vehicle mass, surrounding configuration and vehicle axle configuration.

16. The system according to anyone of the claims 13-15, comprising: - means (200; 210; 500) for determining a first portion of said function (F1) such that itcorresponds to steering action of said front axle wheels (FW1, FW2) from no steering actionup to a first steering action value, the steering action of the rear axle wheels (RW12, RW22) being substantially zero during said first portion of said function (Fl).

17. The system according to anyone of the claims 13-16, comprising: - means (200; 210; 500) for determining a second portion of said function (Fl) such that itcorresponds to steering action of said front axle wheels (FW1, FW2) from said first steeringaction value to a second steering action value, the steering action of the rear axle wheels(RW12, RW22) increases preferably continuously with increasing steering action of said front axle wheels (FW1, FW2).

18. The system according to anyone of the claims 13-17, comprising: - means (200; 210; 500) for determining a third portion of said function (Fl) such that itcorresponds to steering action of said front axle wheels (FW1, FW2) from said second steering action value to a third steering action value, the steering action of the rear axle 27 wheels (RW12, RW22) increases with increasing steering action of said front axle wheels (Fwl, Fwz).

19. The system according to claims 18, comprising: - means (200; 210; 500) for determining a third portion of said function (Fl) such that thesteering action of the rear axle wheels (RW12, RW22) increases more rapidly than during said second portion of said function (Fl).

20. The system according to claims 18 or 19, comprising: - means (200; 210; 500) for determining a third portion of said function (Fl) such that thesteering action of the rear axle wheels (RW12, RW22) comprises a maximum allowable steering action value.

21. The system according to anyone of the claims 13-20, comprising: - means (200; 210; 500) for determining said second portion of said function (Fl) such that the steering action of said rear axle wheels (RW12, RW22) is initiated smoothly.

22. The system according to anyone of the claims 13-21, comprising: - means (200; 210; 500) for determining (200; 210; 500) said function (Fl) for said thirdportion of said function (Fl) such that it is adapted to said second portion of said function (Fl).

23. The system according to anyone of the claims 13-22, comprising: - means (200; 210; 500) for determining if said vehicle (100) is set for reverse propulsion or forward propulsion; and 28 - means (200; 210; 500) for determining said function (Fl) on the basis of the direction of propulsion.

24. The system according to anyone of the claims 13-23, comprising: - means (200; 210; 500) for determining said function (Fl) such that said first portion corresponds to an interval of zero steering action of said front axle wheels (FW1, FW2).

25. A vehicle (100) comprising a system according to any one of claims 13-24.

26. A computer program (P) for steering a vehicle (100) comprising a front axle (FA) and arear axle (RW2), wherein said computer program (P) comprises program code for causing anelectronic control unit (200; 500) or a computer (210; 500) connected to the electronic control unit (200; 500) to perform the steps according to anyone of the claims 1-12.

27. A computer program product containing a program code stored on a computer-readablemedium for performing method steps according to anyone of claims 1-12, when saidcomputer program is run on an electronic control unit (200; 500) or a computer (210; 500) connected to the electronic control unit (200; 500).