SE539451C2 - Articulated Vehicle and Method for Controlling an Articulated Vehicle - Google Patents

Abstract

17 Abstract An articulated vehicle (100) has first and second vehicle parts(F; R) interconnected via a pivotable joint (J). The first vehiclepart (F) contains a first pair of steerable wheels (111, 112) who-se steering angle (öf) relative to the first vehicle part (F) is cont-rollable in response to a first control signal (C(ös)) from an ope-rator-controlled actuator (115). The second vehicle part (R) con-tains a second pair of steerable wheels (141, 142) whose stee-ring angle (ör) relative to the second vehicle part (R) is control-lable in response to a second control signal (C(ör)). A processorin the articulated vehicle (100) is configured to: receive the firstcontrol signal (C(Ös)); receive a signal (l\/l(öa)) representing ameasured articulation angle (öa) between the first and secondvehicle parts (F; R); and based thereon, generate the secondcontrol signal (C(öf)). (Pig. 1b)

Description

AND PRIOR ART The present invention relates generally to control mechanismsfor articulated vehicles. More particularly the invention relates toan articulated vehicle according to the preamble of claim 1 and acorresponding method of controlling an articulated vehicle. Theinvention also relates to a vehicle, a computer program productand a non-transitory computer readable medium.

An articulated vehicle includes a bendable section, normally inthe center, to allow the vehicle to be maneuverable around cor-ners despite its overall length, which may be considerable. Eachsection has at least one wheel axle. However, to improve theload capacity, the vehicle may be provided with one or more ad-ditional axles at the rear and/or front section. To improve themaneuverability, the rear section also often has a steerable ax-le. The steering angle of the rear axle is typically controlled pro-portionally to an amount steered by the driver on the frontwheels. For example, a hydraulic system powered by a pumprunning from the engine may accomplish such a linking.

EP 1 847 443 describes a multi-axle steering system for a roadtrain, which each has a steering axle provided with a steeringactuator for wheel angle adjustment, and a control unit for cont-rolling and/or regulating the steering actuators. None of thesteering actuators has a mechanically and/or pneumatically and/or hydraulically acting connection for the wheel angle adjust-ment to a steering actuator associated with another steeringaxle. A proposed method for operating a multi-axle steering sys-tem determines the nominal set point for the wheel steering ang-le of the wheels connected to an axle is carried out in a controlunit and an output variable which corresponds to the nominalwheel steering angle is determined and fed to a steering actu- ator associated with a steering axle. The multi-axle steering sys-tem is for a road train including at least two vehicle units, suchas an articulated omnibus. The individual vehicle units of theroad train are better able to follow the radius predetermined bythe leading vehicle when turning or negotiating bends.

US 7,793,965 discloses a tractor/trailer combination, wherein atrailer is connected to a tractor through a kingpin with a fifthwheel provided with a trailer steering system. Using given di-mensions of the tractor/trailer combination and a measured arti-culation angle between the tractor and trailer during a turn, thewheels of the rear axles of the trailer are turned so that theyturn approximately about the instant center established for thetractor. ln this way, the trailer turns around approximately thesame point as does the tractor, thus significantly eliminating offtracking.

PROBLEIVIS ASSOCIATED WITH THE PRIOR ART Consequently, solutions are known for controlling articulated ve-hicles having one or more bendable sections. However, theknown control algorithms, which may involve controlling thesteering angle of a rear (non-front) section of the vehicle in aproportion to the steering angle of the front section may result inrelatively poor maneuverability, especially when reversing thevehicle.

SUMMARY OF THE INVENTION The object of the present invention is therefore to solve the abo-ve problem, and thus offer improved maneuverability for articula-ted vehicles both in forward and reverse motion.

According to one aspect of the invention, the object is achievedby the initially described articulated vehicle, wherein the vehiclehas at least one processing unit configured to receive the firstcontrol signal and receive a signal representing a measured articulation angle between the first and second vehicle parts.Based on the received signals, the at least one processing unitis configured to generate a second control signal, for controllingthe second pair of wheels relative to the second vehicle part.

This articulated vehicle is advantageous because the rear sec-tion part can be steered in any relation to the front section, e.g.non-linearly and/or with opposite sign, i.e. contrary to the frontsection over some angular ranges.

According to one preferred embodiment of this aspect of the in-vention, a first processing unit is communicatively connected toa first storage area holding a description of a first relationshipbetween the first control signal and the first steering angle. Mo-reover, the first processing unit is configured to derive the firststeering angle based on the first control signal and by accessingthe first storage area. Thereby, the first steering angle can bederived in a straightforward manner, for example based on alookup table. This, in turn, vouches for a stable and reliable imp-lementation.

According to another preferred embodiment of this aspect of theinvention, a second processing unit is communicatively con-nected to a second storage area holding a description of a se-cond relationship between: the first steering angle and a virtualwheel angle representing an angle at which a virtual wheelwould have been oriented at the first steering angle had the vir-tual wheel been located at the pivotable joint and arranged on avirtual tag axle extending through a center of rotation for thefirst pair of wheels. The second processing unit is configured toderive the virtual wheel angle based on the first steering angleand by accessing the second storage area. Consequently, an in-termediary variable in the form of the virtual wheel angle can bederived in a straightforward manner, for example based on alookup table. Again, this vouches for a stable and reliable imple-mentation of the proposed control algorithm.

According to yet another preferred embodiment of this aspect ofthe invention, a third processing unit is communicatively connec-ted to a third storage area holding a description of a third rela-tionship between: the articulation angle, the virtual wheel angle,and the second steering angle. The third processing unit is con-figured to derive the second control signal based on the articu-lation angle, the virtual wheel angle and by accessing the thirdstorage area. Consequently, the second control signal (i.e. forcontrolling the second pair of wheels relative to the second ve-hicle part) can be derived in a straightforward manner, for ex-ample based on a lookup table, which, of course, vouches for astable and reliable implementation of the proposed control algo-rithm.

According to a further preferred embodiment of this aspect ofthe invention, the description of the third relationship specificallyexpresses the second steering angle in relation to a differencebetween the articulation angle and the virtual wheel angle. Na-mely, this has been found to provide compliant maneuverabilityof the articulated vehicle. ln any case, the above-mentioned first, second and/or third rela-tionships may be expressed in terms of an algorithm instead ofvia a lookup table.

According to still another preferred embodiment of this aspect ofthe invention, two or more of the first, second and third proces-sing units are implemented in a common processing moduleand/or two or more of the first, second and third storage areasare implemented in a common storage module. Naturally, this isefficient from an implementation point-of-view.

According to yet another aspect of the invention, the object isachieved by the method described initially, wherein the secondcontrol signal is generated based on the first control signal anda signal representing a measured articulation angle between thefirst and second vehicle parts. The advantages of this method, as well as the preferred embodiments thereof, are apparent fromthe discussion above with reference to the proposed system.

According to a further aspect of the invention the object isachieved by a computer program product, which is loadable intothe memory of a computer, and includes software for performingthe steps of the above proposed method when executed on acomputer.

According to another aspect of the invention the object is achie-ved by a non-transitory computer readable medium, having aprogram recorded thereon, where the program is make a compu-ter perform the method proposed above when the program isloaded into the computer.

Further advantages, beneficial features and applications of thepresent invention will be apparent from the following descriptionand the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is now to be explained more closely by means ofpreferred embodiments, which are disclosed as examples, andwith reference to the attached drawings.

Figures 1a-b show a side-view and a top-view respectively ofan articulated vehicle to which the present inven-tion can be applied; Figure 2 illustrates a set of angles of measures referring tothe articulated vehicle of Figures 1a-b when tur-ning; Figure 3 shows a block diagram over a processor accor- ding to one embodiment of the invention for cont-rolling an articulated vehicle; Figures 4a-c contain graphs exemplifying different control func-tions implemented by the proposed processor when controlling the articulated vehicle, and Figure 5 illustrates, by means of a flow diagram, the gene-ral method according to invention for controlling an articulated vehicle.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE IN-VENTION lnitially, we refer to Figures 1a and 1b showing a side-view anda top-view respectively of an articulated vehicle 100, exemplifiedby a bus, having first and second vehicle parts F and R that areinterconnected via a pivotable joint J. The first vehicle part Fcontains a first pair of wheels 111 and 112 of which a first stee-ring angle ör relative to the first vehicle part F is controllable inresponse to a first control signal C(ös) from an operator-control-led actuator 115, typically represented by a conventional stee-ring wheel. However, other operator-controlled actuator 115 areequally well conceivable, such as a joystick or a handlebar. Thesecond vehicle part R contains a second pair of wheels 141 and142 of which a second steering angle ör relative to the secondvehicle part R is controllable. ln the embodiment of the invention shown in Figures 1a and 1b,the first pair of wheels 111 and 112 are arranged on a firstwheel axle 110s at a distance fr from a second wheel axle 120of the first vehicle part F. The second wheel axle 120, in turn, isarranged at a distance f2 from the pivotable joint J. A pair ofnon-steerable wheels 131 and 132 are arranged on a third wheelaxle 130 of the second vehicle part R, and at a distance r1 fromthe pivotable joint J. The second pair of wheels 141 and 142 arearranged on a fourth wheel axle 140s at a distance rg from thethird wheel axle 130.

Analogous the first steering angle öf, the second steering angleör is also controlled in response to the operator-controlled ac-tuator 115, However, the second steering angle ör is controlledindirectly and in further response to other parameters. More pre-cisely, according to the invention, the second steering angle ör is controlled in response to a second control signal C(öf), which,in turn, is based on the first control signal C(ös) and a measuredarticulation angle öa between the first and second vehicle partsF and R.

To enable such control, the articulated vehicle 100 contains atleast one processing unit. Figure 3 shows a block diagram overone embodiment of the invention including first, second andthird processor 310, 315 and 320 respectively for controlling thearticulated vehicle 100.

The first processor 310 is configured to receive the first controlsignal C(ös). The first processing unit 310 is communicativelyconnected to a first storage area 312 containing a description ofa first relationship fsf between the first control signal C(ös) andthe first steering angle öf. The description of a first relationshipmay be in the form of a lookup table or an algorithm. A lookuptable is generally advantageous due to its simplicity and robust-ness. lt is also relatively straightforward to model a complex re-lationship by means of a lookup table that is derived from mea-surements. On the other hand, an algorithm may provide ahighly efficient control mechanism. ln any case, the first processing unit 310 is configured to derivethe first steering angle öf based on the first control signal C(ös)and by accessing the first storage area 312. For example, thefirst processing unit 310 may receive a signal l\/l(öa) representingthe measured articulation angle öa, obtain a value from a lookuptable in the first storage area 312, and generate the first stee-ring angle öf.

The second processing unit 315 is communicatively connectedto a second storage area 317 containing a description of a se-cond relationship ffv between the first steering angle öf and avirtual wheel angle öv.

Referring now to Figure 2, the virtual wheel angle öv representsan angle at which a virtual wheel 201 would have been oriented at the steering angle öf if the virtual wheel 201 had been locatedat the pivotable joint J and if the virtual wheel 201 had been ar-ranged on a virtual tag axle TAv extending through a center ofrotation RCf for the first pair of wheels 111 and 112.

The second processing unit 315 is configured to derive the vir-tual wheel angle öv based on the first steering angle öf and byaccessing the second storage area 317. Thus, the second pro-cessing unit 315 may derive the virtual wheel angle öv analo-gous to the above, i.e. by receiving the steering angle öf, obtai-ning a corresponding value from a lookup table in the secondstorage area 317, and based thereon, generating the virtualwheel angle öv. Alternatively, the second processing unit 315may determine the virtual wheel angle öv based on the steeringangle öf and an algorithm stored in the second storage area317.

The third processing unit 320 is communicatively connected to athird storage area 322 containing a description of a third rela-tionship favr between: the articulation angle öa, the virtual wheelangle öv and the second steering angle ör. The third processingunit 320 is configured to derive the second control signal C(öf)based on the articulation angle öa, the virtual wheel angle öv,and by accessing the third storage area 322. Thus, the third pro-cessing unit 320 may receive the virtual wheel angle öv and thesignal l\/l(öa) representing the measured articulation angle öa,obtain a corresponding value from a lookup table in the thirdstorage area 322, and based thereon, generate the second cont-rol signal C(ör). Alternatively, the third processing unit 320 maycalculate the second control signal C(ör) from values of the vir-tual wheel angle öv and the signal M(öa), and based on an algo-rithm stored in the third storage area 322.

Figures 4a, 4b and 4c represent graphs that exemplify the rela-tionships stored in the storage areas 312, 317 and 322 respec-tively. For illustrating purposes, each of the graphs both repre-sents discrete values (i.e. samples corresponding to the con- tents of a lookup table), and continuous functions (i.e. equiva-lent to an algorithm). ln an actual implementation, however, onlyone representation is necessary.

Figure 4a shows the steering angle öf as a function fsf of the firstcontrol signal C(ös). As can be seen, the relationship is herenon-linear. Although this is generally desirable, a linear relation-ship is likewise possible, i.e. that the steering angle öf is propor-tional to the control signal C(ös) from the operator-controlled ac-tuator 115 (e.g. a steering wheel). ln any case, the sign of thesteering angle öf is always equal to the sign of the control signalC(ös). ln other words, a positive steering wheel angle corres-ponds to a positive steering angle öf, and vice versa.

Figure 4b shows the virtual wheel angle öv as a function ffv ofthe steering angle öf. As can be seen, the function ffv is alsonon-linear, which is generally preferable to attain good maneu-verability of the articulated vehicle 100. According to the inven-tion however, the exact relationship described by the function ffvmay be varied somewhat given that the sign of the virtual wheelangle öv is always equal to the sign of the steering angle öf.

Figure 4c shows the second steering angle ör as a function favrof a difference öa-öv between the articulation angle öa and thevirtual wheel angle öv. Analogous to the above, the function favris preferably non-linear. lt should also be noted that, for virtualwheel angles öv larger than the articulation angle öa, the rela-tionship is sign reversed. ln other words, for such articulationangles öa, the second steering angle ör will have a sign that isopposite to the sign of the first steering angle öf, thus prima fa-cie counteracting the input from the operator-controlled actuator115 in the form of the first control signal C(ös). Nevertheless,the inventor has found that this type of relationship provides anintuitive driving behavior, especially when reversing the articula-ted vehicle 100. Consequently, the maneuverability improves.

Returning now to Figure 2, we see that the location of an appro- ximate center of rotation RCf for the first vehicle part F is dif-ferent from the location of an approximate center of rotation RCrfor the second vehicle part R. Such a relationship may not beoptimal from a tire wear point-of-view. Thus, the above-descri-bed improved maneuverability is partially achieved at the expen-se of tire wear relative to an alternative control algorithm wherethe centers of rotation RCf and RCr coincide. For busses in cityenvironments, improved maneuverability is normally more desi-red than a lowest possible tire wear. However, if for example,instead the user would like to minimize the tire wear, the pro-posed embodiments of the invention using lookup tables renderit straightforward reprogram the control algorithms for genera-ting the second control signal second control signal C(ör) accor-dingly.

Of course, although the first, second and third processing units310, 315 and 320 respectively have been described as separateunits, two or more of these units may equally well be implemen-ted in a common processing module. Moreover, alternatively, oradditionally, at least two of the first, second and third storageareas 312, 317 and/or 322 may be implemented in a commonstorage module. ln such a design, two or more of the relation-ships represented in the Figures of 4a to 4c are preferably com-bined into a composite relationship, either in the form of a look-up table or an algorithm.

Preferably, the first, second and third processor units 310, 315and 320 contain, or are in communicative connection with amemory unit storing a computer program product, which con-tains software for making the processor units program product isrun on the processor units. ln order to sum up, and with reference to the flow diagram inFigure 5, we will now describe the general methods executed inthe at least one processor unit according to the invention inorder to perform a chassis-level adjustment operation and there-after return to the nominal level respectively. 11 A first step 510 receives a first control signal C(ös) expressing anoperator input, for example indicated via a steering wheel. Astep 520, parallel to step 510, receives a signal M(öa) represen-ting the articulation angle, i.e. an angle öa measured between afront vehicle part and a rear vehicle part.

Then, a step 530 generates a second control signal C(ör) based onthe first control signal C(ös) and the signal M(öa) representingthe articulation angle.

A step 540, subsequent to step 510, controls an angle of a first pairof steerable wheels on the front vehicle part in response to thefirst control signal C(ös). Analogously, a step 550 subsequent tostep 530, controls an angle of a second pair of steerable wheels onthe rear vehicle part in response to the second control signalC(ör).

Thereafter, the procedure loops back to steps 510 and 520.

All of the process steps, as well as any sub-sequence of steps,described with reference to Figure 5 above may be controlled bymeans of a programmed computer apparatus. Moreover, al-though the embodiments of the invention described above withreference to the drawings comprise a computer apparatus andprocesses performed in a computer apparatus, the invention thusalso extends to computer programs, particularly computer pro-grams on or in a carrier, adapted for putting the invention intopractice. The program may be in the form of source code, objectcode, a code intermediate source and object code such as inpartially compiled form, or in any other form suitable for use inthe implementation of the process according to the invention.The program may either be a part of an operating system, or bea separate application. The carrier may be any non-transitoryentity or device capable of carrying the program. For example,the carrier may comprise a storage medium, such as a Flash me-mory, a ROM (Read Only Memory), for example a DVD (DigitalVideo/Versatile Disk), a CD (Compact Disc) or a semiconductor 12 ROM, an EPROM (Erasable Programmable Read-Only l\/lemory),an EEPROM (Electrically Erasable Programmable Read-OnlyMemory), or a magnetic recording medium, for example a floppydisc or hard disc. Alternatively, the carrier may be an integratedcircuit in which the program is embedded, the integrated circuitbeing adapted for performing, or for use in the performance of,the relevant processes.

The term “comprises/comprising” when used in this specificationis taken to specify the presence of stated features, integers,steps or components. However, the term does not preclude thepresence or addition of one or more additional features, inte-gers, steps or components or groups thereof.

The invention is not restricted to the described embodiments inthe figures, but may be varied freely within the scope of theclaims.

Claims (8)

1. 2G 3G 13 Ctairns t. An artiotiiated vehiote (H30) having first and second vehicieparts (F; R) interoonnected via a pivotabie joint (ti), the first ve-hiote part (F) containing a first pair of wheeis (tft, ftíš) ofwhich a first steering angie (br) reiative to the first vehicie part(F) is controiiabie in response to a first controi signat (Hög)front an operator-controited aotoator (115) and the second ve-hicie part (R) containing a second pair of witeeis (141, M2) ofwhich a second steering angie (di) retative to the second vehictepart (R) is controitabie in response to a second oentroi signa)(Coïšfi), oharaeterized in that the articaiated vehicie (tGG) cont~prisas at ieast one processing unit (Ett), 3t5, 325)) configoredtc: receive the first controi signai (C(öt)), receive a signai (i\!i(öa)) representing a measured artiooia-tion angie (de) between the first and second vehicte parts (fä R),and based thereon generate the second controt signa) (Cföihšwherein a first orooessino unit (319) of the at ieast one orooes~sind unit is oontnftunicativeiv connected to a first storaae area(Stå) contprisino a description of a first retationship (får)between: the first controi sidnai (Gäst) and the first steerind anoie (di), andthe first prooessino unit (316) is ccnfioared to derive the firststeerino annie (di) based on the first controi sionai (CRM) andbv acoessino the first storaoe area (312),wherein a second processind nnit (M5) of the at ieast oneprccessind unit is ocninitinicativeiv connected to a secondstorade area (BW) contorisino a description of a second reia-tionship (fn) between: the first steerind anoie (di) and a virtuai wheei andie (öv) representind an anoie at which avirtoat tfvheei (Edt) wouid have been oriented at the first steerinoanoie (of) had the virtuai wheei (Edt) been iocated at the oivot-abte ioint (J) and arranoed en a virtoai tao axie (Trav) extendino 1G 2G 3G “ifi thtetieh a center et retatien (RQ) ter the tiret eair et wheeie'ätt til? anti the eeeend ereeeesine unit (315) ie eeniieiired te cierive the vir-ttiai wheei aneie (öv) based en the first eteerine aneie (ef) andhv aeeeeeine the eecenti stetaee area (BW), andwherein a third ereeeeeine unit iišåti) et the at ieaet eneereeeeeine unit ie eemmenieativeiv connected te a third eteraeearea (322) eetnerieine a deserietien et a third reiatiehehie (ta-Vf)between: the artietiiatien aneie iš-QL the virttiai tvheei aneie töif). and the eeeenti eteerine aneie (ö) the third ereeeseine unit (BEG) is eentietireci te eerive theeeeenci centret sienai (Ciëii) based en the artieiiiatien annietea). the virtiiai wheei aneie (öv), ane hv aeeeeeine the third ste» rage area tfiêê). 2G 3G eg, "the artictiietea vehicie (ttiG) acceraing ta ciaint e i,wherein the deecriptian ei the third reiatienehip (tat-f) expreeaeethe secanci eteering angie (är) in reiatian ta a ciitterence bettfveenthe articuiatian angie (53) ana the vittnet wneei angie (öv). eg The articuiatert vehicie (ttiti) accarciing te any ane afciaiine å ¿t_ w gr ä g, tfvherein at ieaet two ct the tiret, second andthird processing units (310, 315, 320) are intpientented in aaaninian arcceeeing rriaatrie ancifcr at ieaat twe at the first,eecand and thirci eterage areas (ïštâ, Siï, 322) are irnpiementedin a carrtrncn eterage meciuie. %¿t_. "the artiauiated venicie (iüü) aaccrtiing te any ane ct äreQreceding ciainie nå, wherein the first, second and third reta-ticnehiee (tai, fn, ige) are expressed in terrne et et ieaet ane at aieakua taisie ana an aigarithni. 1G 2G 3G “itš ågí. A niathaci of cantraiiing an articuiatad vahicia (199) havingfirat and aacand vahicia parts (3 R) intarcannactaizi via a pivat~abia iaint (J), tna firat vahiaia part (F) caritaining a firat pair atataarapia whaaia (fit, H2) and tna aaaana vahicia part (R)containing a saaand pair of ataarabia whaaia (tfiii, 142), tha rna-tnart carnprising: cpntraiiirig tha firat pair af ataarahia whaaia (i i t, itä) tp afirat ataaring angia (år) raiativa ta tha first vahicia part (F) in raa~panaa ta a first aantrai aignai (Cßsi) frarn an aparatanaantraiiaciaatiiatar (i 15) in tha articuiatad vanicia (ttiti), and aantraiiirtg tha aacpnci pair af ataarahia tivhaaia (Mt, 142)ta a aaaond staaring angia (är) raiativa ta tha saaonci vaniciapart (R) in raapanaa ta a aacanti aantrai aignai (Citta),charaatarizaa ny: ganarating tha aaaana cpntrai aighai (Ctëiß) haaaa an thafirat aantrai signai ((2453)) anti a signai (it/Hög) rapraaanting antaaatirari articiiiatian angia (53) hatwaait tna firat and aacanrivanicia parts iF; RLtha firat staarina ariaia (är) nairia datarrniriaci iaaaaa an a firatraiatianahip (tai hatwaan tha first contrai sianai (Ctëiiii and thastaarina anciia (ört. tha ntathad fiirthar aantprisinci: datarrniriiha a virtiiai tfiihaai anaia (öv) rapraaaritina ah ana-ia at which a virtuai whaai (2913 watiia hava haarf ariantatt at thafirat staarina anaia (är) hart tha virtuai Whaai (låtit) naan iarzataciat the pivatabia iaint (Ji and arranciad an a virtuai taa axia (TAV)axtandina thraiiah a cantar at ratatian (Rtilfi far tna firat pair atwnaais titt, “ii2i isaaaci an a aaaana raiationsnip natwaan thafirst ataarina anaia (är) and tha virtaai Whaai anaia (ätt-i, and datarrninina tha sacana ataariria anaia iñfi based an a thirdraiatianahip itavii batwaart tha artiatiiatian anaia (öaä. tna virtuaiwhaai anaia (ör/i, and tha aacarfd ataarina anaia (år). Zíi t? "the ntethed eeeerding te eteirn tfvherein the third reåe»tienehie (tavf) exereeeee the eeeette steerâng enete (år) in re»ietien te e difference between the ertieetetieit engie (ett) ene thevittnet wheeä engše (öv). eefi. A eentptiter etegrern eredeet ieettehie inte e ittentery et etieest ene eeaneuter, eentprieing eettware ter eertermiawg thesteps et the ntethed eeeerding te eny et the eieirns »êet=%ë 5 er 6when exeeeted en the et ieest ene eenfteeter. eeåßt nen-treneitery eenteeter reedeeše nteeietn having e ere-grern reeerciee thereen, where the nregrern is te make et ieeetene computer eerterrn the steps et eny et the eieinte 5 er6,