Direct Current Measurement Based Steer-By-Wire Systems for Realistic Driving Feeling Tien Si Nguyen...

7/27/2019 Direct Current Measurement Based Steer-By-Wire Systems for Realistic Driving Feeling Tien Si Nguyen Ba Hai

1/6

IEEE International Symposium on Industrial Electronics (ISlE 2009)Seoul Olympic Parktel, Seoul, Korea July 5-8, 2009

Direct Current Measurement Based Steer-By-WireSystems for Realistic Driving FeelingBa-Hai Nguyen', Jee-Hwan Ryu'

1School ofMechanical Engineering, Korea University of Technology and Education, Cheonan , Korea(E-mail: [email protected])2School of Mechanical Engineering, Korea University of Technology and Education, Cheonan, Korea(E-mail: [email protected])

Abstract - In this paper, a method to reproduce realisticdriving feeling and improve the returnabili ty of steer-by-wiresystems (SBW) is proposed by measuring the roadwheel motor'scurrent directly. The key contr ibution presented here is a novelmethod to recreate the driving feeling in term of force feedbackwith simpie and cheap current sensors. A current sensor is used tofully measure the steering torque on the rack of steer ingmechanism. This measured steering torque therefore, includes theoverall effects of road conditions, aligning moments, tireproperties and so on. Beside that, a free control scheme isproposed to improve returnab ili ty as well as the handwheels tab il ity in a free motion. Moreover , dur ing this research , thesignificant frequency effect of handwheel motions was found. Thiseffect could be useful and valuable for improving steer-by-wiredevelopment based on torque-map based method. This method isinvestigated with simulation results using the control design andsimulation module in LabVIEW programming language. Thesimulated results show that this method offers a cheaper andsimpler solution for the development of steer-by-wire systems. Inaddition, stability and returnability of handwheel in steer-by-wiresystems could be improved.

I. INTRODUCTIONSteer-by-wire is the innovative version of an automotive

steering system shown in Fig. 1. In the SBW system, a drivingsignal given by a driver is transmitted to the road wheelsthrough electrical wires while this signal is transmitted throughmechanical and, or hydraulic linkages in conventional steeringsystems.Thanks to the absence of the mechanical connection between

the handwheel (HW) and the roadwhee l (RW), SBW systemsoffer several advantages such as lager space in the cabin,freedom in car interior design, no oil leaking, and less injury incase of car accidents . However , the re are also numbers ofdisadvantages due to the lack of mechanical connection. Forexample, the lack of real is tic driving feelings, which is thedriving feelings for the driver as in conventional steeringsystems. SBW systems can be out of order because of electricalfaults. In addit ion, the difficulty of the free control of thehandwheel , which is the HW behavior, after the driver's handsrelease at certain steered position of the HW. One of the mostchallenging issues on SBW development is how to give driversthe rea lis tic fee lings or rea li st ic force feedback which is thesame as convent iona l hydraul ic s tee ring systems. The forcefeedback for SBW systems has been studied by manyresearchers, [1], [2], [4], [5], [9]. In 1966, E.R Hoffmann [1]

and P.N. Jouber studied on the effect of changes in somevehicle handling variables on driver steering performance.In 1995, Andrew Liu and Stacey Chang [2] descr ibed three

experiments conducted in a driving simulator that explore howforce feedback info rmation may be used by the dr iver and tosee how steering torque information is affected by the varianceof the steering movements. Recently, disturbance observerbased approach is implemented by Yih, P. and Gerdes, J.C.[13], and Shoji Asai, 2004 [5], etc. For this method, thereal is tic feelings could be obtained from the dynamic modelusing an observer. However , the exact model s of steeringsys tem and vehicle as well as powerful microcontrol le rs areessential here.Some papers [15], [16],have proposed a torque map-based

method, in which, the force feedback can be ob tained wi th aforce control loop. A to rque map is a reference input of theforce feedback control . This torque map is the combination ofseveral signals such as vehicle velocity, HW angle, etc.Attaching torque sensors to the rack of the steering system isproposed by PI [16]. However, prices and heavy workingconditions of torque sensors in steering system are the biggestdisadvantages for those methods.In this paper, we propose a novel method to make the

realistic feelings in the SBW system the same as the drivingfeelings in hydraulic power steering systems. This method isinexpensive, easy to develop, and less complexity.

II. STEER-BY-WIRE SYSTEMA. Conventional mechanically connected steering and SBWIn conventional mechanically connected steering systems,

such as hydraulic power assisted steering systems, Fig. 1a; theHW rotation given by a driver is transmitted via a intermediateshaft. The co lumn is connected to the rack and roadwheels.Therefore, the roadwheel angle is proportional to the HWrotation. An ampli fied hydraul ic pump is used to reduce thedriver's steering efforts.In SBW, Fig. 1b, the intermedia te shaft, and the hydraulic

pump are removed. And several position sensors and actuatorsare attached to the HW and RW. The encoder at HW is toobserve HW motion. The HW motion, then converted intoelectrical signals and wired to an electronic control unit (ECU).The ECU controls an RW actuator for rotat ing the RW part inthe same manner of the HW behaviors. The second encoder at

1023978-1-4244-4349-9/09/$25.00 2009 IEEE


2/6


3/6

b i h+ ~ .. R\\' A1llonthm

RWl>I Ol'"Torquc

as a teleoperation system with position-force controlarchitecture [6], [9], Sanket Amberkar and et. al. worked on Acontrol system methodology of steer-by-wire systems based onposition-force control scheme (Fig. 5).

Torq".Command

the align moment is considered as a source of disturbance inthe system dynamics. Therefore, the aligning torque can beestimated without any torque sensors. However, disturbancebased approach requires a powerful microcontroller forcalculating the force feed back. And the estimated signal maybe not exactly the same as the actual aligning moment.B. Torque map-based methodTorque map method is a good way to avoid the calculationof aligning moment for solving force feedback issue. One ofthe torque maps is developed by Se-Wook Oh & et. al. Theirmain concept was the torque map is built based on two signals,vehicle velocity and HW position, Fig. 4. In particular, therelationships between the HW angle and vehicle velocity aredefined as equation (3), and (4).

Displacementsensor,,,,

RW(DCmotor,

IV. DIRECT CURRENTM EASUREMENTMETHOD

MASTERIHW)

Fig. 5 Position-force control scheme

A. OverviewofdirectcurrentmeasurementmethodIn our proposed method, there are two control loops Fig. 6. Infirst loop, HW encoder detects HWmovements and sends HWangle as an input to a PID position controller. Then, thecontroller gives control signal as current signal to RW actuator.The position synchronization of the HW and RW is ensured bybe the PID controller. RWangle 8m plays a role as feedbacksignal.

HW(DCmotor)

Driver'ssteeringtorque

feedbackposition

POSITION CONTROL (PID)- - - - - - - - - - - - - - - - - - - - ~ - - - - - - - - - - - - - - - I, I

IIII- - - - - i - - - - - - + - - - - ~ - - - ,reference i measured 1 :

current i current i FREE CONTROL

CONTROLLER1- - -- - - - --IIIII

~ - - - - - - - - - - - - - - -

When the RW DC motor actuates the roadwheelsaccordingly, a proportional current signal inside the motordriver of occurs at the same time. Fortunately, the value of thecurrent signal depends on the load applied on motor shaftbecause of the current-torque relationship of DC motors.

, . S _ ~ V ~ i R ~ L ,-IIIIIIIIIII

~ - - - - - - - - - - - - - - - - - - - _ ! ~ ~ - - - - - - - - - - - - - - - - - - - - -Fig. 6 Overview of steer-by-wire structure

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ~ - - - - - - - - - - - - ,desired i feedbackposition i force

Ysw = Ka,JO;: (3)Velocity effect term:

2 I IYv = - K px ("3x -"2Vvmax)+T,n (4)

Where Ka , Kp are constants defined by developers. Vv max isthe vehicle's maximum velocity. x is vehicle velocity. T,n isthe initial torque. The summation of angle effect term Ysw andvelocity effect term Yv is the total force feedback (or called asdriving feeling) in this method. With the torque map, it is easyto recreate force feedback because the HWangle Bhw , and thevehicle velocity Vv can be easily measured in any todayvehicles. However, other factors such as rotating frequency ofHW, aligning moment, and so on, are not considered in thistorque map.Seok-Hwan Jang [14] and et. al., in 2003, proposed afeedback force calculation scheme based on reference model ofHW with lateral force measured from a torque sensor. For this,there is no need of the second torque sensor at RW while theforce feedback is governed only by reference model of HWand the measured aligning torque.C. Torque sensor-basedmethodResearchers from the field of robotics have proposed torquesensor based solution in which a steer-by-wire system is treated

Fig. 4 Control scheme of the torque map methodAngle effect term:

1025


4/6

A current sensor unit is connected to RW's motor driver andRW's motor in series for measuring current signals. This signalis later used for creating force feedback. To create realisticfeedback, the vehicle speed and the HW angle are employed toproduce the assistance force. To make HW stable and easy tobe controlled, a free control algorithm is developed based onthe HW angle. The next section will comprehensively describethe force feedback implementation and free control.B. ReproducingdrivingfeelingAs discussed in section III, force feedback contains momentsof inertia, damping, and Coulomb friction and aligning force.The force feedback of I-IW is proposed in equation (5). Wherei is RW actuator current. This current tells the RW part'sproperties which are various depending on steering systemmechanism, road condition, side-slip angle, and so on. Tre is afree control torque discussed in section V.C in this paper.

T/ eedbaek = G/ee/ (K, . i - Tassis, ) + Tre (5)Basically, in automotive power steering, the assistant torqueis used to reduce the force feedback at the lower speed (thespeed of the vehicle) or tighter at the higher speed [6].Therefore, assistant toque Tassis, is introduced in equation (6).

From equation (5) and (6), the total force feedback isreproduced. In particular, this feedback torque is tuned throughthree steps. First, pure force is calculated from the measuredcurrent signal. This torque is quite hard like steering systemwithout any assistant means. Therefore, assistant torque basedon the equation (6) is done in the second step. We may turnI-IW angle gain K a , and velocity gain ; to obtain the desiredforce magnitude. In the third step, there is a need to tune twogains ( G fe el' and K fc ) at the same time to achieve a desiredforce feedback profile. A gain set selected in this research isprovided in the table of simulation parameters [Table I].C. Free controlTraditionally, free control response has been solved by addingdamping (in the case of EPS) or friction to the system [6] (inthe case of hydraulic steering). In previous research, a freecontrol algorithm for EPS application is done by Bolourchi andEtienne [12]. Sanket Amberkar, et al mentioned that for thefree control of a steering systems as well as SBWsystems, aquick return ofI-lW to center with minimal overshoot is desired[6]. However, their research did not mention how a good freecontrol is implemented. Our proposed idea is to add additionaldamping to SBW system. Thus, we now introduce a newtorque to the system called free control torque. This torque is aproduct of a free control gainK fc ' and I-IWangle, written inequation (7).

T/e = - K re *0 hw (7)By introducing this force to the system, the force feedbackwill change. Fortunately, because the special design of nonphysical connection of by-wire technology allows us to easily

adjust the force feedback by changing the HW angle gain andvelocity gains or the scaling factor of RW motor's torque inequation (5).V. SIMULATION

A. Overview ofsimulationPID controller for position control of steering system aims tohave a good position tracking of RW and HW. An open loopcontrol for force feedback based on the measured current signalis conducted as algorithms described in section 4. Free controlquality is evaluated by the returning force verse HW angle,[15]. Simulation parameters are chosen as follows.TAB! E I SIMULATION PARAMETERS.III' : 0.019 (kg.m"2/s"2) The ine rt ia and damping constan t o f s te er ing syst emThese constants are chosen based on s teering sys temb l' : 0.368 (Nms) identification done by [131Gjeel : 1 This gain is selected based on comfortable feelings ofdriversK, : 0.581 (NmjAmp) From themotordatasheetKa :0 .3 Assistance gain is chosen based on amount of desiredtorque and feedback torque profilesK ,. :3 Assistance gain is chosen based on the amount of desiredtorque and feedback torque profilesV. : 60 (km/h) A certain velocity selected fors imulating inthis paperKfe : 0.02 This is selected based on the behaviors of free control. Inthe best case, this gain ensures lowest oscillations of HW

in free controlKp :5.5, Kd : 0.08 These are gains of PDcontroller.Turning method: Ziegler-Nichols

B. Simulation resultPosition tracking, A good position tracking also can beachieved in this method shown in Fig. 7. The simulationparameters are: K p =5.5; Kd =0.08; Step size: 0.001 (s).The result shows that error of the system is significantlyreduced. In this method, the error is about 0.06 rad) while it isnormally about O. I - 0.59 rad mentioned in [10], [I5]. Theresult of postion tracking in J-command is shown in freecontrol of HW (Fig. 15). The J-commend is defined as a quickchange in I-1W input. This command is given by the driverwhen an obstacle is suddenly found.

'U~ 0,5-v-g D-. .,c

- o , 5::;:-1.1: i--,--,-- :;: ' - -- .-- ,--,-- :;: ' - --.--, - o

Fig. 7. Position tracking ofSBWRealistic haptic feedback, the force feedback is first

recreated based on current signal without any amount ofassistant force and free control force. In addition, without tireto-ground contact, the relationship of HW angle as forcefeedback is a rectangular profile shown in Fig. 8.

1026


5/6

7.5- ,- -- - - - - - - - - - - -5.0-

contributions which are not solved in torque map-basedapproach.Proposed methodTMHPS

5.0-E- ; 2.5-::Jc-5 0.0f0> -2.5- iyoo..................._ - ;:l1 , ;til -5.0 -

7.5- ,- -- - - - - - - - - - - -t 2.5- [ ]5 0.0f- -2.5 -1 - - - - - - - - - - "oJVl -5.0-

-60 .0 -40.0 -20 .0 0.0 20.0 40.0 60 .0HandwheelAngle (deg)

-7.5- 1 I , , I ' I t I ' , , I I I I I ' , , I I I , I

-7.5- 1 ' , , I I , , I ' , I I ' , , I I , , I ' I , I-60.0 -40.0 -20.0 0.0 20.0 40.0 60.0HandwheelAngle (deg)

40.0, , ,-20 .0 0.0 20.0Handwheelange (del;l

-3.5-,-60.0 -40 .0

Fig. II . Comparison of proposed method and othersHPS: hydraulic power steering, TM: torque-map method

In addition, with the direct current measurement method, theforce feedback can be abstained and easily adjusted Fig. 12. Inthis result we have three torque profiles equivalent to the freecontrol gains are 0.01, 0.02, and 0.03. For the result of totalforce feedback shown in Fig. 11, the free control gain is chosenas 0.02.

Fig. 8. HW position vs. Force feedback without tire-to-ground contact

10.0 -

-15.0- 1 I , , I ' I I I I I I I ' , , I I I I I I , I I-60.0 -40.0 -20.0 0.0 20.0 40.0 60.0HandwheelAngle (deg)

15.0 - , - -- - - - - - - - - - - -

E- ; 5.0s

0.0 -l; -5.0-.oJVl -10.0 -

In normal working condition, the tires travel on road surfaceand aligning torques at two front wheels happen. When thesteering angle increases, the aligning torque become largerbecause of the increment of the pneumatic trail shown in Fig.9.

Fig. 9. HW position vs. Force feedback with tire-to-ground contac1The final force feedback is achieved after introduction ofassistant torque based on HW angle and vehicle velocity, Fig.10.7.0- , - -- - - - - - - - - - - -

E 4.0~ " 2.0 -s5 0.0 f- -2.0 -" -4.0 --7.0 - 1 ' , I I I I , I I I I I I , , I I I I I ' , , I-60.0 -40.0 -20.0 0.0 20.0 40.0 60.0

Handwheel Angle (deg)Fig. 10. HW position vs. Force feedback with assistant torque

Fig. 11 is the comparison of simulation of torque mapmethod and the proposed method. The simulation result clearlyshows that, the proposed method can achieve the realistichaptic feedback which provides the realistic driving feelings.In our proposed method, the steering dynamics is included toimplemented force feedback. These dynamic effects arerepresented in term of current signal. Therefore, the obtainedforce feedback not only depends on HW angle and vehiclevelocity, but also relates to road condition, tire properties, yawmovement of vehicle and so on. This is most the benefit

Fig. 12. Different force feedback magnitude with varying free control gain

The rotating frequency of HW is changed from 0.05 to 2Hzin different experiments. The results in Fig. 13 show thatsteering torque is significantly affected by HW frequency. Thisis an important finding because this effect is ignored in torquemap based method.7. - - - - - - - - n ~ i i i i i i i ; ~ ~5.0-E~ 2.5 -":Jsr 0.0-

0>. -2.5-"oJVl ~ ~ ~ : : : :

-7.5- 1 ' , I I I , , I I I , I I I I I I I I I ' I I I-60.0 -40.0 -20.0 0.0 20.0 40.0 60 .0HandwheelAngle (deg)

Fig. 13. Different force feedback magnitude with varying free control gainFree control, the simulation result in Fig. 13and Fig. 14 hasproved that, the free control torque has significantly reduced

1027


6/6

s Simulation Time (5)

VI. CONCLUSIONA ND FUTUREWORK

This work was supported by the grant for industry-universitycooperation laboratory program in 2009.

REFERENCES

[8] Cortesao, R.; Bajcinca, N., "Model-matching control for steer-by-wirevehicles with under-actuated structure", Intelligent Robots and Systems,Proceedings. 2004 IEEE/RSJ International Conference, vol. 8, pp. 1148 1153, 1966.

[1] E.R. Hoffmann and P.N. Joubert, "The effect of changes in some vehiclehandling variables on driver steering performance", Human Factors, vol.8, 1966, pp. 245-263.[2] Liu, A. Chang, S., "Force feedback in a stationary driving simulator",Systems, Man and Cybernetics Intelligent Systems for the 21st Century.,IEEE International Conference, Canada, vol. 2, pp. 1711-1716, 1995.[3] D. Odenthal, T. Bunthe, H.-D. Heitzer, and e. Heiker, "How to makeSBW feel like power steering", Proceedings of the 15th IFAC WorldCongress on Automatic Control, Barcelona, 2002.[4] 1m, lS .; Ozaki, F.; Matsunaga, M.; Kawaji, S., "Design of SBW systemwith bilateral control method using disturbance observer", Advancedintelligent mechatronics, 2007 IEEE/ASME international conference,2007.

[8] Askun G'uven, Levent G'uven, "Robust steer-by-wire control based onthe model regulator", Proc. of the 2002 IEEE Intenational Conference onControl Applications, Glasgow , 2002,[9] M. Segawa, "A study of reactive torque control for SBW system",Proceedings of 7th Symposium on Advanced Vehicle Control, 2002.[10] S.Wook, "The development ofan advanced control method for the SBWsystem to improve the vehicle maneuvrability and stability", Proceedings

ofSAE International Congress and Exhibition, 2003.[II ] D. Heitzer and A. Seewald, "Development of a fault tolerant SBWsteering system" SAE Technical Paper Series, 2004.[12] F. Bolourchi & e. Etienne; "Active damping controls algorithm for anelectric power steering application"; Proceedings of: 30th InternationalSymposium on Automotive Technology & Automation - pp. 807-816;June '97.

[5] Shoji Asai, Hiroshi Kuroyanagi, Shinji Takeuchi, "Development of aSBW system with force feedback using a disturbance observer", Steering& Suspension Technology Symposium: Steering, SAE 2004 WorldCongress & Exhibition, Detroit, MI, USA, 2004.[6] Sanket Amberkar, Farhad Bolourchi, Jon Demerly and Scott Millsap, "Acontrol system methodology for steer by wire systems", SAE WorldCongress, Detroit, Michigan, 2004.[7] F. Bo lourchi & e. Etienne, "Active damping controls algorithm for anelectric power steering application", Proceedings of: 30th InternationalSymposium on Automotive Technology & Automation, pp. 807-816,

1997.

[13] Yih, P. Gerdes, J.e . , "Modification of vehicle handling characteristicsvia steer-by-wire", Control Systems Technology, IEEE Transactions ,vol. 13, pp.965- 976, 2005.[14] Seok-llwan Jang; Tong-Jin Park; Chang-Soo lIan, "A control of vehicleusing SBW system with hardware-in-the-Ioop-simulation system",Advanced Intelligent Mechatronics, AIM 2003. Proceedings. 2003IEEE/ASME International Conference, vol I, pp.389 - 394,2003.[15] Oh S-W, Chae H-C, Yun S-C, Han C-S "The design of a controller for thesteer-by-wire system", JSME Int Journal. Ser e. Mech Systems, MachElemManuf, Japan, vol47, pp.896-907,2004 .[16] Bing Zheng; Altemare, e. ; Anwar, S., "Fault tolerant steer-by-wire roadwheel control system", American Control Conference, vol 3, pp. 16191624,2005 .[17] Oniwa yoshihiro "Stabilization on a Control for Moment of Inertia ofEPS", Proceedings. JSAEAnnual Congress, 2006.[18] Julien Coudon, et. aI., "A New Reference Model for Steer-By-WireApplications with Embedded Vehicle Dynamics", IEEE AmericanControl Conference, 2006.

, ,, ,Simulation Time (5)

SetP'3'lxn pn ,RW'_ Ji";'fi\ ~VI. ./f lin ........

-------.::!!

s ~ , _ ~ PD I. l W '_ V ;s,s i""", /I: ' o:s .'-'.s IIIs,s

Fig. 14. HWbehavior without free control torque ( Tic)(Without scaling of HWangle andWR angle)

This research have proposed a novel control scheme forsteer-by-wire development in which the current sensor couldbe used to fully measured steering torque . Since, currentsensors are cheap and available in typical industrial andautomotive applications. This solution offers a cheaper andsimper method to reproduce the driving feeling. The forcefeedback control algorithm is developed not only to give therealistic driving feelings, but also improve the returnability andfree control performance while remain the fundamentalrequirements of conventional steering systems such as positiontracking.We suggest that, for steer-by-wire systems, a study of forcefeedback of very light handwheel in novel design ofhuman/vehicle interfaces. In this case, handwheel 's massshould be included in force calculation scheme to recreatedriving feelings which is the same as conventional powersteering systems. In addition, the study of different forcefeedback of different handwheel types might be benefit forsteering control of vehicles. The lock-to-Iock properties ofsteer-by-wire happened at the largest steering angle will beimplemented in the near future.ACKNOWLEDGEMENT

the oscillation of HW. This could be explained easily becausewhen the free control factor is added to the system, thehysteresis of steering system is reduced shown in Fig. 11. Thehysteresis of proposed method is reduced to -5 to 5 degreeswhile it was from -10 to 10degrees in torque map method.

Fig. 15. HW behavior with free control torque (T ic)(Without scaling of HWangle and RWangle)

1028

Direct Current Measurement Based Steer-By-Wire Systems for Realistic Driving Feeling Tien Si Nguyen...

Documents

Transcript of Direct Current Measurement Based Steer-By-Wire Systems for Realistic Driving Feeling Tien Si Nguyen...