The effects of changes in understeer, control sensitivity, and location of the lateral aerodynamic center of pressure (c.p.) of a typical passenger car on the driver's opinion and on the performance of the driver-vehicle system were studied in a moving-base driving simulator. Twelve subjects with no prior experience on the simulator and no special driving skills performed regulation tasks in the presence of both random and step wind gusts

Alexandridis, A. A.

Repa, B. S.

Wierwille, W. W.

English

NASA Technical Reports Server

r-_
THE_INFLUENCE OF VEHICLE AERODYNAMIC AND CONTROL
RESPONSE CHARACTERISTICS ON DRIVER-VEHICLE PERFORMANCE
by
Alexander A. Alexandridis
Brian S. Repa
Engineering Mechanics Department
_ General Motors Research Laboratories
Warren, Michigan 48090
Wal.ter W. Wierwille
Virginia Polytechnic Institute and State University
h Blacksburg, Virginia 24061
SUMMARY
\
C
The effects of changes in understeer, control sensitivity, and location
of the lateral aerodynamic center of pressure (c.p.) of a typical passenger
car on the driver's opinion and on the performance of the driver-vehicle
system were studied in the moving-base driving simulator at Virginia Poly-
technic Institute and StateUniversity. Twelve subjects withno prior
experience on the simulator and no special driving skills performed regula-
tion tasks in the presence of both random and step wind gusts.
INTRODUCTION
The performance of the driver-vehicle system in the presence of cross-
wind disturbances is influenced by the location of the lateral aerodynamic
center of pressure (c.p.) of the vehicle.
The extent to which changes in c.p. location are discernible and/or
objectionable to ordinary drivers has up to this time been unknown. Most
of the previous studies on wind gust disturbance regulation tasks have
concentrated on a single c.p. location with the c.p. most frequently
placed at the front wheels (references 1-5). Also, although the influence
of changes in d_sign parameters, such as understeer and control sensitivity,
have been studied previously (references 3, 4), the interaction of these
parameters with the location of the c.p. in a closed-loop task is unknown.
The present study examines the influence of various combinations of
understeer, control sensitivity, and c.p. location on the performance of
twelve ordinary drivers in the presence of wind gust disturbances.
The Virginia Polytechnic Institute and State University (VPI&SU) moving-
base driving simulator was chosen for the tests because of the control it
offers over the parameters of interest and because of the success of previous
research performed'with th_ facility (reference i). The following sections
279 .._ ,.4
1979007417-272
https://ntrs.nasa.gov/search.jsp?R=19790007437 2020-03-20T18:13:51+00:00Z
describe the simulation facility, the experimental design and procedure
employed, the performance measures utilized, and the results obtained.
THE VPI&SU DRIVING SIMULATOR
This experimental facility provides the subject with an on-line, com .....
puter-generated, television-type display of the roadway in coordination with
the motion cues of yaw and roll, as well as lateral and longitudinal trans-
lation. In addition, four channels of sound along with vibration are pro-
vided for the enhancement of the simulation realism.
Three separate inputs were provided to the vehicle model used for the
! simulation; namely, steering wheel displacement, accelerator/brake displace-
ment, and aerodynamic force (wlnd gust). The model consisted of a set of
I transfer functions relating the three inputs to the vehicle motion compo-
i nents.
!
References i, 6, and 7 contain a detailed description of the driving
i simulator and related equipment; figure 1 shows the simulator motion plat-
i fo_.
DEFINITIONS AND EXPERIMENTAL PROCEDURE
r,
Definitions
The three experimental variables are defined briefly as follows:
i. C.p. location, x a : The distance between the front-wheel axis
and the point of action of the lateral aerodynamic force Fa
(see figure 2).
This variable is expressed as a percentage of the vehicle wheelbase
(xa = 0.0% corresponds to a c.p. IQcation at the front wheels).
2. Understeer, K : The numerical difference between the sideslip
angles developed at the front and rear wheels during a l-g lateral
acceleration.
Understeer is conventionally measured in deg/g. A more detailed descrip- }
tion of this concept is given in reference 8. Figure 2 shows the paths
that vehicles with understeer (K) 0), neutral steer (K = 0), and over-
steer (K < 0) would follow under the influence of ar external side force
acting at the center of gravity.
280
.._
.= |
1979007417-273
!
I
J
3. Control sensitivity, C.S. : The steady-state lateral acceleration |
(in g's) developed by a vehicle following a steering wheel displace-
ment of 1.75 rad (i00.0 deg).
Experimental Design
A mixed between-subjects and within-subjects factorial design was
used, containing two levels of understeer (K = 3.0, 5.0 deg/g), two _I _i
levels of control sensitivity (C.S. = 0.8, 1.2 g/lO0 deg), and three c.p. _.
locations (xa = 0%, 19%, 37% of wheelbase) for a total of twelve vehicle _
configurations. Six male and six female college students without any
previous simulator experience were used as subjects. Three male and three •
female subjects were randomly assigned to each of the two understeer condi-
tions (understeer was a between-subjects variable). The other two variables
were factorially complete and equally likely for all subjects. The subjects
were given a 1.5 min period of practice following which they were required
to maintain a constant speed of 97 km/h (60 mph) while keeping their normal
lane position in the presence of random wind disturbances. Data were
collected for a period of 2.0 min. Following the random wind disturbances,
i a series of step gusts were presented for an additional 2.0 min period. At
the end of each run, the subjects rated the disturbances they encountered,
taking into account the vehicle path deviations and the amount of steering i_ 4
! activity needed to maintain course. _
Data Collection
The time histories of the vehicle lateral position and yaw heading
deviations, as well as the driver's steering wheel inputs were recorded
_ on an F.M. tape recorder. The objective measures of performance were the
_i root-mean-square (rMs) values of these time histories, together with the _
_. peak lane overshoots during the step gusts.
RESULTS
Subjective Ratings
Figure 3 shows that the subjective ratings improve as the c.p. moves
i rearward. The other two variables had no significant effect on the ratings°
i Random Disturbance Performance
Significant differences in lane-keeping performance occurred as a
result of changes in C.S. and xa . There is a shrong indication of an
Ii ii
281 :
19790074]7-274
Ieffect on lateral position deviation due to an interaction between under-
steer and c.p. location and a significant effect from this interaction on
yaw deviations.
Figure 4 shows that increases in both C.S. and x a result in decreases
in lateral position deviations. The nature of the interaction between K .....
._ and xa that approached significance in shown in figure 5_ The higher
value of understeer has a beneficial effect on lateral position deviations
only when the c.p. is located close to the front wheels. Figures 6 and 7
show similar effects for yaw angle deviations.
Steering wheel deviations were significantly affected by all three
vehicle parameters. Furthermore, there were significant effects due to
interactions between c.p. location and understeer and between c.p. location
and control sensitivity.
Figure 8 shows that increases in K, C.S., and x a all have a similar
effect; namely, to decrease steering deviations. Figure 9 reveals that
increases in both K and C.S. result in greater decreases in steering devia-
tions the closer the center of pressure is to the front wheels.
Step Disturbance Performance
The peak lane position overshoot was measured from the actual vehicle
. position prior to the gust onset and not from the center of the lane. i
Figure i0 shows that increases in x a and in C.S. reduce peak lane
position overshoot. The effects of understeer were accentuated as the
c.p. location moved forward, with the lower level of understeer resulting
in the largest lane position overshoot.
i
DISCUSSION i
The subjective and objective measures used in the present study !
indicate that c.p. location is an extremely important parameter for wind
gust regulation performance. Scores on the 0-10 Rating Scale, maximmn
lane deviations following a step wind gust, and steering wheel deviations
during presentation of the random wind gust were all highly significantly
affected by changes in c.p. location. Actual lane position deviations
during the random wind gust task were only slightly less sensitive to
, changes in c.p. location than these other measures.
In spite of its great importance, however, c.p. location is difficult
to control in practice (reference 9). For this reason, other means for
improving disturbance responses of the closed-loop driver-vehicle system !
were explored; namely, through changes in understeer and control sensitivity, i
Both parameters were found to have a significant effect on wind gust regula-
1979007417-275
tion performance, although subjective opinion data failed to d_tect _his
effect. Increased levels of understeer (K = 5.0 deg/g vs.3.0 deg/g) and
control sensitivity (C.S. = 1.2 g/100 deg vs 0.8 g/100 deg) both had a
beneficial effect on measures of path control and driver steering wheel
deviations. These beneficial effects were accentuated where they were
needed the most; namely, at forward c.p. locations, i ....
CONCLUSIONS -
The following conclusions were reached:
eDriver opinion ratings were significantly influenced by c.p. ,
location only, with rearward locations rated the most favorable.
oLane-keeping accuracy improved as the c.p. moved rearward
as control sensitivity increased.
and
_i OFor the forward c.p. locations, lane-keeping performance
improved with increased understeer.
i eSteering wheel activity required for control was reduced by
I increased understeer and control sensitivity and by rearward
movement of the c.p., with the effects of understeer and
_ control sensitivity accentuated at forward c.p. locations.
Overall, the location of the aerodynamic center of pressure was the
predominant vehicle characteristic with an influence that could only
partially be offset by changes in understeer and control sensitivity.
h
_ REFERENCES
_: i. Repa, B. S.; and Wierwille, W. W.: Driver Performance in Controlling *_
i a Driving Simulator with Varying Vehicle Response Characteristics.
SAE Paper No. 760779, 1976.
2. Repa, B. S.; Zucker, R. S.; and Wierwille, W.W.: The Application
I of Integral Performance Criteria to the Analysis of Discrete Maneuversin a Driving Simulator. Proc. Thirteenth Annual Conference on Manual
_: Control, 1977.
3. Repa, B. S.; Alexandridis, A. A.; Howell, L. J.; and Wierwille, W. W.:
Study of Vehicle Steering and Response Characteristics in Simulated
and Actual Driving. SAE Paper No. 780011, 1977.
4. McRuer, D. T.; and Klein, R. H.: Automobile Controllability -- Driver/
Vehicle Response for Steering Control. Systems Technology, Inc.,
Vol. I, Summary Report, Contract No. DOT-HS-359-3-762, 1975.
283
1979007417-276
5. Crossman, E.; and Szo_tak, H.: Man-Machine Models for Car Steering.
Fourth NASA-University Conference on Manual Control, NASA SP-214,
1968,
r
6. Wierwille, W. W.: A Part-Task Driving Simulator for Teaching and
Research. Computers in Education for ASEE Transactions, December I
19_3.
7. Wierwille, W. W.: Driving simulator Design for Realistic Handling.
Proc. Third International Conference on Vehicle System Dynamics.
Swets and Zeitlinger, B. V., Amsterdam, 1975.
8. Bundorf, R. T.; and Leffert, R. L.: The Cornering Compliance Concept
for Description of Vehicle Directional Control Properties. SAE
Paper No. 760713, 1976.
9. Bundorf, R. T.; Pollock, D. E.; and Hardin, M. C.: Vehicle Handling
Response to Aerodynamic Inputs. SAE Paper No. 716B, 1963.
i
_ 284
,,, ,
1 .Q7.QNN7zI 17_977
I
OR|G_AL pAGE IS'
OF pOORQUALITY
ag
z
o
2
n
m
m
285
. J
]9790074]7-278
IUNDERSIEER '_
UNDERSTEER\
\NEUTRAL.,
i
F
FIG. 2 DEFINITIONS
286
1979007417-279
.- i o'_' q
lO
,.H
v'l
2_'
i0
0 ]9 37
,! C.P. LOCATION( _ WHEELBASE)
' FIG. 3 DEPENDENCEOF SUBJECTIVERATINGSOF VEHICLE
CONFIGURATIONSON C.P. LOCATION
!.
IL
f.
I.
1979007417-280
45. 45'
i _ 0 = ..... ]---
0.8 1,2 o 19 37
CONTROLSENSITIVITY C.P. LOCATION I_ WHEELBASE)(G1100DEG)
FIG. 4 EFFECTSOF CONTROLSENSITIVITYAND C.P. LOCATION
ON LATERALPOSITIONDEVIATION(RANDOMWIND GUST)
i
t
! 288
1979007417-281
-55 1 & K- 3.0DEGIG ""i
• K - 5,0 DEGI G ."
i'I
40
ol , ....., ,
0 19 37
C.P. LOCATION(5 WHEELBASE)
FIG. 5 COMBINEDEFFECTSOFUNDERSTEERAND
C.P. LOCATIONON LATERALPOSITION
DEVIATION(RANDOMWINDGUST)
_ 289 :.-'-
!
1979007417-282
! .8'
.T' .7,
f g E ....... '
.I' .4, .
_ .3, _
z
<.2'
>c
...... 19......._' 0 : 0.8 1.2 0 0 37
CONTROLSENSITIVITY C.P,LOCATION('&WHE(LBA,SE)
(GI 100DEG)
FIG. 6 EFFECTSOF CONTROLSENSITIVITYAND C.P. LOCATIONON
YAW ANGLEDEVIATioN (RANDOMWIND GUST)
290
,, 1979007417-28
oJ
0
0 19 37
C.P. LOCATION(5 WHEELBASE)
"%
FIG, 7 COMBINEDEFFECTSOF UNDERSTEER
AND C,P. LOCATIONON YAW ANGLE
DEVIATIONtRANDOMWIND GUST)
291 _
,._
.,................ 1979007417_28,4-..,.
!. ,. ,
18' 18'
i !'
! _ 12. ,2,
IO3.0 S.O O.S 1,2
• UNDERSTEER(DEGI G| CONTROLSENSITIVITY(OI I00DEG)
15'
lO'
0
0 19 37
C.P. LOCATION(% WHEELBASE)
FIG. 8 EFFECTSOF UNDERSTEER,CONTROLSENSITIVITY,AND
C.P. LOCATIONON STEERINGWHEELDEVIATION(RANDOM ,
WIND GUST)
292
_-_:-:': ...........................-"- .... - 1979007417-28_
0 i i I 0 i I,, t ,
_- 0 19 37 0 19 37
C.P. LOCATION(% WHEELBASE) C.P. LOCATION(% WHEELBASE)
FIG. 9 COMBINEDEFFECTSOF UNDERSTEERAND C,P. LOCATION
AND OF CONTROLSENSITIVITYAND C.P. LOCATIONON
STEERINGWHEELDEVIATION(RANDOMWIND GUST)
293
L ii ._
1979007417-286
,e •
. !
!
14( FIRST GUST
EE
13[
E o
120" FIRSTGUST _ 120 P<_ .I
I--
0 e_kIJQ
-_ II0' _ II0
e_
w _ 100o>z0o. 4--
_9o. _ _0I-,-
o z
" 80' <; 80
I ,.," • K " 3.0 DEGI G
z • K • 5.0DEGIG
'_ 70. _ 70
O, J ,, O- t , t t
0.8 Z.2 0 19 37
CONTROLSENSITIVITY
(G I 100 DEG) C.P. LOCATION (% WHEELBASE)
FIG. I0 EFFECTSOFC.P. LOCATION,CONTROLSENSITIVITY,AND
UNDERSTEERON PEAKLANEPOSITIONOVERSHOOT(STEP
WINDGUST)
i
294
".... 1979007417-287


The influence of vehicle aerodynamic and control response characteristics on driver-vehicle performance

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server