2006 IEEEInternational Conferenceon Systems, Man,and Cybernetics
October 8-11, 2006, Taipei, Taiwan
The
Human-in-the-loop Design
Approach to the
Longitudinal
Automation System for
the
Intelligent Vehicle, TAIWAN
iTS-i
Hsin-Han
Chiang, Jau-Woei Perng, Bing-Fei Wu, Shinq-Jen Wu, and Tsu-TianLeeAbstract-This paper presents the integration design and implementation of alongitudinal automation system with the interaction ofhuman-in-the-loop (HITL). Theproposedsystem has a hierarchical structure composed and consists of an
adaptive sensory processor, a supervisory control and a
regulation control. The adaptive sensory processor routes the information from on-board sensorstoavoidmissing detection of thevehicle ahead. Based ontherecognized measurementfrom the adaptive sensory processor, the supervisory control determines the desiredvelocityfor thevehiclesoas tomaintain safetyandsmoothoperationindifferent modes. Theregulation controlutilizessoft-computing techniqueanddrives the throttle action to execute the desired velocity commanded from the supervisorycontrol. The feasible sensorydistance iswithin40 m, and the according driving velocity can achieve 100 km/h upward. Thechallenge in low velocity operation can also be handled by the regulation control against gear changes and torque converter. Among experimental tests under various kindsoftrafficflows, the systemvalidnessisexhibitedand also the preferable comfort is achieved through theexaminationof international standard ISO 2631.
I. INTRODUCTION
Vehicle automations are currently being introduced into the assistance to relieve human drivers from undesired routines of driving task. Sincemanystudies have shown that over 90 percent ofhighway accidents are occurred due to
driver-relatederrors,themain initiative is toimprove safety ofthe automation system interacted with thehuman driver. As to the vehicle longitudinal automation control, some famous practical works [1-3] introduce the features like adaptive cruise control (ACC). Themoreunderstandings of the automation of vehicle longitudinal control task are provided in [4]. Besides, to increase more capability being with human drivers, the conception ofhuman-in-the-loop (HITL) needstobemoreconsideredintothesystemdesign.
The safety consideration into the vehicle longitudinal automation is the safety headway distance adjustment to
avoidthecollision withthe vehicle ahead. Toaccommodate the automation system to different driving conditions, the
corresponding
operation
modes andthe automatic transition frame should be developed. There is no initial demand for roadenvironment,and alsofor theaction of thehumandriverH. H.Chiang,J. W.Perng, B. F.Wu, and T. T. LeearewithNational Chiao-TungUniversity, Hsinchu, 300, Taiwan,R.0. C.(authorstoprovide
phone:886-3-5712121-54346;fax:886-3-5729749; e-mail:hsinhan.ece90g @dnctu.edu.tw;jwperng(cn.nctu.edu.tw;bwuQcssp.cn.nctu.edu.tw;ttlee@ cn.nctu.edu.tw)
S. J. Wuis with Da-YehUniversity, Changhwa, Taiwan,R.0. C.(e-mail:
jen(dmail.dyu.edu.tw)
I 1 OMNi VOOO , I;:Svw;
Fig. 1. Overall structure ofthehuman-in-the-loop longitudinal auto-mation system.
which can be viewed as a disturbance to the automation system. It is essential to consider the adequatestability and robustness into the controlling design. Moreover, drivers' comfort is also the most important initiative counted for automationdesign.
This paper proposes the longitudinal automation
system,
which is implemented on a real vehiclenamed TAIWAN iTS-1,with the interaction of the human driver. Thespecial modificationstotheautomation system are toensure safety and smooth operation with workload reduction for the human driver. Finally, experimental results in real road environments document the performance of the overall system integration extended to the capability of HITL design.II. SYSTEM CONFIGURATION AND OBJECTIVES AsillustratedinFig. 1,theroad environmentmainlyrefers
to the longitudinal direction in front of the subject vehicle, andtheon-boardsensorsinclude laser radar andanglesensor
of thesteering wheel (SW). The adaptive sensoryprocessor deals with measurements fromradaraccordingtothe action of humandriver andthevelocityofthe vehicle. Basedonthe recognized data, the supervisory control makes thedecision of operation modes and desired velocity command to the
regulationcontrol for the execution ofvelocity tracking. The throttlepedalisdrivenbythelongitudinalautomation system
toachieve thecontrollingobjective. Althoughthe brakepedal
TABLE I
CRITICAL THRESHOLD OF COMFORTINISO 2631 STANDARD Nodiscomfort ( -0.315 m/sA2)
Alittle discomfort (0.315 0.63m/sA2)
Somewhat discomfort (0.5 -1m/sA2) Discomfort (0.8 1.6m/sA2)
Extremely discomfort (1.25 -2.5m/sA2) Verydiscomfort (2 m/sA2 )
and reserved for the human driver totake the awareness of emergency.
As far as the longitudinal automation convinced to the human driver isconcerned, the controllingoperation for the subject vehicle comprises thevelocity tracking cruise mode and automatic vehicle following mode. In the velocity tracking cruise
mode,
theobjective is to controlthe subject vehicle to track any desired velocity commanded from the human driver.Atthetimeof thedetectionfrom thepreceding
vehicle, theautomation system will automatically switchtothe automatic vehiclefollowingmode. The objective ofthis modeistomakesureofsafety headway distancemaintaining forthesubject vehicle without the need of vehicle-to-vehicle (v-v)communication. Inaddition,the automation system will automatically switch back to the
velocity tracking
cruise mode if there isnovehicle detectioninthe front.In these both operation modes, the ride comfort of the human driver or passengers isconsideredintotheautomation design. As the comfort analysis concern, the international standard ISO 2631-1:1997 [5], which defines the means to
evaluate vibration with respect to human responses, is employed to examine the ride
quality
of theproposed
longitudinal automation system. This standard specifies direction and location of measurements, equipment to be used, duration ofmeasurementsandfrequency
weighting,
aswell as methods of assessment of measurement and evaluation ofweightroot-mean-square(r-m-s) accelerationin meterspersecondsquared
(m/s2).
The index ofthis standard is determinedbythefrequency-weighted
acceleration whichcanbecalculatedby usingtheexpressionas
a=
(Wa.)
2 ,(1where
a,
denotesfrequency-weighted
acceleration,
Wi denotes theweightingfactor ofinteresting
axesofbody,
and ai denotes ther-m-s acceleration for the i-thone-thirdoctaveband.
The comfortanalysisisassessedby checking thata,, over sampledhorizon doesnotreachacritical thresholdvalue,as
depictedinTableI. Astothelongitudinal automationdesign, the motion which performs in the
longitudinal
axis is the interesttobeexaminedfor ride comfort ofthesubject vehicle. Thefollowing section describes the designingapproachfor the longitudinal automation system to be assured that the safetyand comfortrequirementscanbe both achieved.III. LONGITUDINALAUTOMATIONSYSTEMDESIGN In this section, the three components of the proposed vehicle longitudinal automation system are introduced, respectively.
Specified radar dstance
(orheadwaydistance, d)
Look-ahead
offset,Yd
Look-ahead distance d.
Adaptvescanningangle 20. 'II,
l
Fig. 2. Illustration ofthevehiclefollowingscenario on curved roads.
A. Adaptive Sensory Processor
As illustratedin Fig. 2, thepreceding vehicle can not be detectedby the laserradar in front ofthe followingvehicle if the scanning beam is too narrow. This fact might bring the emergency due todrastic acceleration action of the system. Nevertheless, if the scanning beam is too broad, some unexpected objects which areneighborwith theroad will be detected. Therefore, it is necessary to design the adaptive sensory scheme such that the preceding vehicle can be correctly detectedevenifonthecurved roads.
Byconsidering theturning behaviorof the vehicle, a linear bike model of lateral dynamics from steering angle
gf
to lateralvelocityv,
andyaw rate r is employedas[V!]
+LvX
Bg
(2)
where
_
_f+
)-aCr
+bC,I
j CA=
Ka
+'>Ct;(a2Cf +b2C)
jr
B Lidaand bdenotethe distances fromthefront andrearaxlesto thecenterofgravity (CG)of thevehicle, mdenotesthe total
massofthevehicle, Vdenotes the forward velocity,
A,
denotes the yaw moment ofinertia, andCf
andCr
denote the total corneringstiffnessofthe frontandreartires, respectively.Inaddition,todetect theexistence oftheprecedingvehicle, the look-ahead information of the subject vehicle must be considered. The dynamics of the point at a look-ahead distance of themoving vehiclecanbedescribedas
d =
Ved
-v, -rd£ad
V/Rf
-r(3) (4) where Ydand
6d
denote the lateral offset from the centerline and theangle between tangent to the road and the vehicle at a look-ahead distanced,andRJ
denotesthe road curvature.Notethat here the roadcurvatureisrestricted to be constant for theassumptionofthesteady-state analysis. The reason is that the vehicle will notreach a steady-state condition while travelinga road with varying curvatures, and then the static relation is difficulty to be investigated. As shown in Fig. 2, the subject vehicle (or called following vehicle) and the preceding vehicle both travel a curve with a constant
TABLE II
(9f,
0)WITHVARYING VELOCITIES AND RADIUS OF CURVED ROADSRf 200m 300m 400m 500 m v 40 km/h (19.6,6.9) (14.5,5.1) (10.9,3.8) (8.7,3.1) 60km/h (23.9,9.2) (15.5,6.1) (11.6,4.6) (9.3,3.7) 80km/h (25.1,11.9) (16.8,7.9) (12.6,5.9) (10.1,4.7) 100km/h (27.6,16.6) (18.4,11.1) (13.8, 8.3) (11.1, 6.6) Unit: degree
curvature
l/Rf.
Byconsidering asteady-state motionthat the subject vehicle tracksthe curvedroadperfectly at a constant velocity, the variationsofthevehiclelateral dynamics (2) and look-ahead dynamics (3) and (4) can be set to zero, i.e.,rv
=r d =ed
=0. In the following, the subscript ofssdenotesthe value atsteady-state condition. Throughdirection calculation, the steady-state steering anglecanbe obtainedas
1 mV (aCf-bCr)
Rf (a+b)CfCr
Thesteady-state look-ahead lateral offset canbe adoptedas
Y,/s =
hss
-Rf
(6)
where h - R2
+d2+2Rfd(-v,ss
V)Besides, at steady-state the lateral dynamics (2) can be
presented
asALvs -Bdf (7)
r5 andthis holds ifandonlyif
v,ss
- T (8)where T=
b+amV2/(a+b)C.
Notethatthefixed values oftheyawrate canbe obtained by
rs2=
V/Rf
(9)whichisassumedinthesteady-stateturning.
By substituting (8) and (9) into (6), the look-ahead steady-state look-ahead lateraloffsetcanberewrittenas
,
Rf2
+d22+2dT
-R(10)
From(5)and(10), oneobtains
Ydss R, R,2+d' +2dT fR (11)
sfs
(a+b mV2(aCbC,
)/(a
+b)Cfr)
Itisreasonablytoassume
d2+2dT /Rj<<1
(12)
and thefollowingapproximation
viaTaylor's
expansion
canbeobtainedas
vRf2 +
d-
+2dT= R + &+2dT (13)2R
Through (13), the relation (
11)
becomesYdss,
d 2dT (14)3,ss
2(a+ bV2P)
where P=
m(aC1
-bC,
)/(a+b)CI
C,.To obtain the relation between the adaptive scanning angle and the steering angle, the followingapproximation is applied as
tanO=
y,
/Id (15)where
d,
denotes the specified distance in the feasible range forlaser radar.By substituting (14) into (15) with the small angle assumption which assumes tan
0.^
,one canobtain0
d2+2dT
Ko
(16)6fs
2d,
(a
+b-V2P)
d,
The real input to the vehicle is the steering wheel (SW), and the steering angle can be substituted with the SW angle through a constant ratio [6], i.e., 3=i4, (normally the value of is isbetween 18and22for passenger vehicles). In(16),the resulting feature is that the adaptive ratio between the adaptivescanning angle and the steering angle is independent ofthe road curvature. It can be observed that the adaptive ratio updates with the vehicle velocity. During the vehicle turning in a higher velocity, the look-ahead lateral offset increases such thatthe scanning beam isturnedmoredegree withthe samedirectiontothe SW. As toless road curvatures, thelook-aheadlateral offset decreasessuch that the scanning angle is turned less degree. TableIIdepicts this result.
B. SupervisoryControl
There are two stages in the supervisory control. In the first stage, thedesired acceleration is determinedaccording to the selected operation mode and available feedback signals. In the second stage, the desired acceleration is converted to the desiredvelocitywhich ispassed into theregulationcontrol.
The velocitytracking cruise mode is to design the desired acceleration such that the subject vehicle can track proper velocities commanded by the driver and avoid feeling discomfort.Define the velocity tracking erroras
eV
-V Vds
(17)
and selecttheslidingsurfaceas
Scc
=e =-Vd,5
(18)
ToforceScc
0,
the controllaw can be chosen asSCc
=-KCCSCC
(I19)
where Kcc >0 is chosenby thedesigner.
Equation
(19)
satisfies the global asymptotically stable requirementand alsoSCcS,
< 0. Notethat thechoiceof(19) usually includes the discontinuous sign function,e.g.,sgn(S), in typical literatures of sliding mode control (SMC). However, thechattering phenomenawill be causedthatalso bringssomeunforeseen noiseofhigh frequency. Instead,the continuous function is feasible to beimplemented
for its simplicity.By differentiating
(18),
the desired acceleration will be easily solved with (19). To achieve therequirement ofride comfort,itshouldkeeptheacceleration commandbounded tothe desiredone
aMfilax
especiallywhile the initialvalue ofevis large. Therefore, theslidingsurface in(18)
can be modified intoaf
+eeRulebas
P.>
Fig. 3. Theblockdiagramoftheclosed-loop velocity regulation control.
wherea1is thecurrentacceleration of thefollowing
vehicle,
andsa(
=x,
f as x <1Is
sign(x),
as.xl
>IFor the case of
laj
+evI<afmax,
the sliding surface (20) is identicaltothe one of(18). The desired acceleration canbe solvedasafd
=Ve,
-K(C(V
-Vt)
(21)
While
laf
+eRI>
ajmax,
thesliding
surface becomesScc
=-at afn-xX
(22)and thedesired accelerationis
a
=d
a a (23)fdes KC'C' fmax
Notethatthejerkin(23)canbe
neglected
forthe intention of constraintinthedesiredacceleration,
i.e.,
afdes=±afmaxThe control law in (21) israther simple. Since only the velocity ofthe subject vehicle is
required
for thevelocity
trackingmode,implementation
of thisdesign
is easyandstill associatedwith theconsiderationof ride comfort.Continuingly, the
objective
of the automatic vehicle following modeforheadway distancetracking
istodesign
the control law of the desired acceleration. Tobegin
with the development of asliding
surface, the vehiclefollowing
dynamics in terms ofusing
the relative distance R arepresentedas
R
Xp
-X(24)
Rk
=Vp-V(25)
whereXand Varethesubject vehiclepositionandvelocity, and
Xp
and VParetheprecedingvehicleposition
andvelocity. Byemployingthefixed
headwaytime strategy,thedesired followingdistance lawaccordingtothevelocityofthesubject vehiclecanbeobtainedbyR,ds
aV+L(26)
Rdes -ca
(27)
wherea isregardedasthedesiredheadwaytime, andLcanbe viewedas aminimum safety distanceortypically avehicle's length.
The error between thedesired and relative headway distance isdefinedas
eR =R-
Res
(28)
andthesliding surfacecanbedesignedas
S;F=
--af+a1masat('+e
R (29)f max
Forthe case of
a1
+eRK<
afmax,
this sliding surface(29) is obviously stable since SVF OaseR O.Bychoosing thesamecontrol law as(19), thedesiredaccelerationcanbederivedas aff1e
I-(K1,,,
SyP +R)
(30)Theresultinthecaseof
laf
+eR
I>
afmax
isthe similarto(23) and the controllawafdes=±
afmax
isused instead. In(30), only theheadway distanceand its changerate arerequired and the stability is alsoguaranteed.
Notethat there isnoknowledge of the preceding vehicle existing in (30). Although the states related to the preceding vehicle can be obtained by v-v communication device, it can notbesupposed that all other vehiclesareequipped.In the second stage, the conversion from the desired accelerationtothevelocityisdesignedas
VcGesa=
cges-k/
(V-Vles
)(31)
where k, >0 isadampinggain.As to the selection logic between these two modes, this autonomy scheme can be achieved by adopting the min-operation in the secondstage,namely,
V1
=min{k7V,Vv,4
(32)
Once the preceding vehicle is detected, the final desired velocity for the subject vehicle will be determined by the automatic vehiclefollowing control, i.e.,
VJ=vVF;
otherwise, thesubject vehicle will be backtothevelocity trackingcruise control, i.e.,Vf
=Vcc.Thisapproachisintuitivebut also easy toimplementation.C.
RegulationControlThe objective of the regulation control is to execute the desired velocity commanded from the supervisory control. The vehicle longitudinal dynamics canbe described by a set of system composed of various linear and nonlinear subsystems, e.g., engine, automatic transmission in the gear box, brake system, and the rubber tires with respect to roads,
etc. Indeed, it is verydifficult for control designing based on this complicated model. As to the ill-conditioned and complexmodel ofvehiclelongitudinal dynamics, it motivates theemployment of fuzzy logic control (FLC) in the regulation controldesign.
TABLE III
FuZZY RULE BASE OF THESFLC
D, NB NS ZO PS PB
u NBu NSu ZOu PSu PBu
INHW JVSI ZO PS PB
-1 -0.2 0 0.2 1
A`ru NSWu ZOo PSa PBRo
-1 -0).7 0.7 1
Fig. 4. Membership function of the fuzzy input(up) and the fuzzyoutput
(below).
The block diagram of the regulation control with the vehicle longitudinal dynamics is shown in Fig. 3. The regulation control scheme is composed of a proportion
-derivative (PD) controller and a FLC. There is a single
control input defined by the error ofthe commanded and
current velocity, i.e.,e=V -V, and the control output is the
applied voltage to the throttle motor actuator. The
characteristics ofthethrottlemotor actuator canbemodeled as one saturation function with a transport delay. H(s, V)
presentsthe dynamics from the derived throttle angleto the
vehiclevelocity.
This PD-type FLC with a single-input is convincingly
representative to the single-input FLC (SFLC) proposed in
[7]. For conventional FLC's, the fuzzy rule base is constructed in a two-dimension (2-D) space for using the error and error change phase-plane, i.e., (e, e?). It can be
inspected thatmost 2-D fuzzyrule bases have the so-called
skew-symmetricproperty.Onenewfuzzyinputcomposedof
theerroranderrorchangecanbepresentedas
Ds
=kde+kle
(33)Therefore, the 2-D fuzzy rule base of the error and error
changephase-planecanbe reducedinto 1-D spaceofDsfor
SFLCaslisted in TableIII.Both therangesof thefuzzyinput
and output arethesamefrom-1 to 1,and thecorresponding
membershipfunctionsareplottedinFig. 4, respectively.
Inthedefuzzication operation, thecenter ofmass(COM)
method isappliedtocalculatethecontrol output
5 5
U = ,Z ,(Ds)xu / u,(Ds) (34)
whereArepresentstheweightingvalue of each rulei,andui
is thecrispvalueof each ruleconsequence.
There are many advantages for applying this PD-type
SFLC. Regardless of the controlled plant dynamics, it
requires onlyone fuzzy input anda 1-D space offuzzyrule
base. Therefore,thenumberoftuningparametersinFLC can
be greatly reduced. The computation load can also be alleviated for that the numberoffuzzyrules is considerably
decreased.
Fig. 5. Theexperimentalscenarioonthe real road environment.
IV. Experimental Results
The proposed longitudinal automation system is implemented on a commercial vehicle named TAIWAN
iTS-I,Savrian, manufactured by Mitsubishimotorcompany.
The feedback velocity of the vehicle is measured from the wheel-velocity instrument of the front left-tire. For the headway distance measurement, one laser radar (LMS291,
manufactured by SICK), is employed to the automation
systembythe connection through RS-232. The permissible
distanceofradar inforwarddirection issetto80m,however,
the feasible distance inpractice is 40m.Astothe angle ofthe scanning beam, the maximum value for radar is 50 degree in bothleft andright planes. Itisassumed that theturning angle for the scanning beam is adaptive to be according to the algorithm derivedin Section III. However,notethat thereis
no auto-turning schemeinthe function ofLMS291, thus in
this work, the acquired sensory distance is determined
accordingtothemeasuredonewiththecalculated expanding
angle of radar.Inaddition, the anglesensorisinstalledaround
the axis of the steering wheel, and through CAN bus tothe automation system. The whole automation is built in the real-time Microautobox (MABX), which is a compact
stand-aloneunit withrapidprototype ofcontroldesign. The
more detailed information of MABX is available at
http://www.dspace.com/ww/en/pub/home/products/hw/mica
utob.cfm. The throttlepedalisadjusted byaDC-motor with
thefeedbacksignal ofthethrottlepositionsensor,toyield the velocity trackingforvehiclecontrol.
To exhibit the validness of the proposed longitudinal automation system, manyexperimentshave bee taken inthe expressway (Chutung-Nanliao segment, Taiwan), in which the legal highest velocity is 90 km/h. The scenario of
experiments attherealroad is illustrated in Fig. 5. Initially
the subject vehicle is in the automatic vehicle following mode, and maintains the safety headwaydistanceaccording
tothecurrentvelocity(about75 km/h). Thesampled history
ofexperimentswiththe scheme ofadaptivesensoryprocessor
isdepictedinFig. 6. As shown in the secondgraph,here the fixedheadwaytime issetas 1 second thesame,suchthatthe
desiredheadwaydistance isabout21 m.There isnomissing
detection of the preceding vehicle during the vehicle
50 60 70 80 90
..I
0 10 20 30 40 00 60 70 00 90 90 ~80~ >700 10 20 30 40 50 60 70 80 90 1 commard 4S ...--measured 0 0 10 20 30 40 50 60 70 80 90 time(sec)Fig. 6.Theexperimental scenarioonthe real road environment.
followingcontrol mode, and thethrottle action also
performs
smooth, asin the bottomgraph. Once thepreceding vehicle changes the original lane, the subject vehicle automatically switchestothevelocity cruisetracking
mode and accelerates totheoriginal
desiredvelocity
90km/h,
asshown in thethird graph.Itcanbeseenthat thesteady-statethrottlevoltage after the acceleration is larger values for thehigher
velocity than the slower velocity. If one vehicle cuts in the forward direction,orradar detects the slowervehicle ahead within the feasible range (40 m), then the throttle pedal of thesubject
vehicle will beadjustedtofollow thepreceding
vehiclewith thesafetydistanceaccording thecurrentvelocity. Besides the high velocityoperation, althoughnotshown,
theoperation
of low velocity (20 km/hupward)
can also be handledby
the regulation control against gearchanges and torque converter of the vehicleengine.During these experimental tests of the
longitudinal
automation system, the acceleration of thesubject
vehicleis recorded forcomfort analysis.Oneaccelerometer is locatedat the center of gravity of thesubject
vehicle foronly
the longitudinal motion is ofinterest.InTable IV, it is clearto see thatthecomfortindexa, withindifferentsampling
intervals areallextremely satisfied with the constraint ofnodiscomfort in ISO2631 standard. Therecorded acceleration data of the subject vehiclearenotrestrictedtoonlyone operation mode but also include the transition process. Even if the human driveractsbraketoomuch such that the vehicleisdecelerated tomuchlowervelocity, yet theautomation systemperforms smooth accelerationtothedesired velocityunder therequest for comfort. Both theselections ofthesaturated accelerationa1
max andheadwaytime acan beadjusted from thehumandriveraccording topersonal driving behavior and favor. The braking action is reserved to the human driver to take the awareness of emergency, while the concentration on maintaining a safety headway distance is delivered to the longitudinal automation system. Therefore, inaddition tothe comfortrequirement,theworkload reductionfromthehuman driver can also be achieved.
TABLEIV
FREQUENCY-WEIGHTEDACCELERATION DURINGDIFFERENTSAMPLING INTERVALS
Sampling interval(sec.) a,(m/s2)
0o 30 0.0522
0-40 0.0688
0 50 0.0585
0 60 0.0755
V. CONCLUSIONANDFUTURE WORKS
Integration ofhuman-in-the-loop designintoalongitudinal
automation designis presentedinthis paper, andtheoverall
system is successfully implemented on apassenger vehicle
testedinreal road environments.Thelongitudinal automation
system is composed of the adaptive sensoryprocessor, the
supervisory control, and theregulation control. The system
safetyisimproved byinclusion ofadaptivesensoryschemeto prevent the missing detection of the preceding vehicle on
curved roads. The supervisory control isdesignedto switch between different modesautomaticallyandoperatewithinthe bound acceleration constraint without therequirementofv-v
communication.Basedonthereference velocitycommanded
from the supervisory control, the regulation control is to
executethevehiclevelocitytrackingthroughthethrottle. The proposed automation system istoassist the humandriver in
the velocityand inter-vehicle space control such asto yield
theworkload reduction ofdriving. Finally, the experimental resultsat real roads verify the validness of the longitudinal automation system. Furthermore, the ride comfort is also achievedthroughtheexaminationofthestandardISO 2631.
ACKNOWLEDGMENT
This work is supported by the program of Promoting
Academic Excellence of Universities under Grant. No. 91X104 EX-91-E-FA06-4-4. We also thank Tseng-Wei Chang and Tien-Yu Liao for the cooperation of hardware work.
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a 10lo ~0 10 I,.-f 10 20 30 40