TOM 5 lipiec - sierpień 2001 r. S fa a b w t& U fi nr 4
Wiesław Pieniążek*, Jerzy Warszczyński**, Borysław Piotrowski**, Grzegorz Hiczwa***
Research of influence of the tyres on steerability of car applying RSV experim ental tests
In this paper the results o f experimental tests o f van type o f car equipped with three sets o f tyre according to Research Safety Vehicle (RSV) specifications is presented.
The m ain results were o b ta in ed on the basis o f R S V returna b ility perform ance test but steady state circular test and steering wheel input test has been also taken into consideration.
In conclusions the results were evaluated from point o f view o f estimation the tyres properties.
Key words: tyres properties, stearability o f car, R S V tests
Badanie wpływu opon na kierowalność samochodu z zastosowaniem
eksperymentalnych prób RSV
W pracy przedstaw iono metodykę oceny wpływu opon na kierowalność samochodu. Podczas badań wykonano eksperymentalne próby stosowane dla tzw .sa m o c h o d u b e zp ie c zn e g o (RSV), tzn. b a d a n ie rea kcji na sko ko w e wym uszenie obrotem kierownicy i badanie zdolności samoczynnego powrotu do ja zd y na wprost.
Badano sam ochód FORD Transit na trzech zestawach opon. W pierw szy z nich, o wym iarach 195R14C, samochód je s t wyposażany standardowo. Dwa następne, o wym iarach 185R14C, różniły się konstrukcją bieżnika i rodzajem mieszanki.
Przedstawiono wyniki badań samoczynnego powrotu do ja zdy na wprost.
Na ich podstaw ie nie stwierdzono zasadniczego wpływu zastosowanych opon na rozpatrywane właściwości samochodu. Potwierdziły to także wyniki innych prób opisanych w pracy.
Słowa kluczowe: właściwości opon, kierowalność samochodu, próby RSV
* Cracow University o f Technology
** Research and Developing Centre o f the Industry “Stomil”, Poznań
£Ca&t&*K&Ufs nr 4 lipiec - sierpień 2001 r. TOM 5
1. Introduction
A m ong testin g o f car p roperties special atten tion deserve testing concerning active safety i.e. its stability and steerability.
A big part in creatin g active safety of car (i.e.
steerab ility and sta b ility ) is being co n trib u ted to tyres. T heir features essential from the point of view of stability and steerab ility are:
• lateral stiffness which influence to cornering stiffness,
• circu m feren tial stiffness - from w hich depend lon gitu d inal forces during drive and braking,
• type and tread pattern - from w hich depend road adhesion and above m entioned long itud inal and lateral forces.
In tyre industry labo ratories are being p erfor
med sp ecialistic produ ct testing, m ainly on testing stands according to adequate program and m etho- dics. There are also being perform ed tyre road tests but m ainly in respect to estim atin g tyre perfo rm an ce durability, no ise level, tread pattern w ater d ra
inage ability and other param eters, but concerning only tyres.
E xam ination o f steerab ility and stability per
form ed on differen t tyre types according to m etho- dics applied to the w hole car can also provide valu able in fo rm a tio n re fe rrin g to tyres. A fter stated changes in car p ro p ertie s one can con clude also about tyre p rop erties.
In this elaboration are presented results of such exam inations perform ed several years at the In sti
tute of A uto m ob ile and Inn er C om bustion Engines C racow U n iversity of Technology and m utual re
search results from R esearch and D eveloping C en
tre of the Tyre Industry “ S T O M IL ” Poznań.
2. Short information
concerning test methodology
At present are available several ISO docum ents concerning m ethods utilised for exam ination of sta
bility and steerability of cars. Four of them are con
sidered as the m ost im portant: ISO 4168 concerning in procedure for steady state circu lar test, ISO 7401 w ith procedure for test of response on various ste ering w heel inputs, T R /ISO 3888 co ncerning p ro
cedure for a Severe L ane-C h ang e M anoeuvre (the so-called “elk te s t” is also applied recently for te sting of car stability and steerab ility) and ISO 7995 concerning for braking on the turn.
One should rem ind here that in the early se
venties was e sta b lish e d In te rn atio n a l C om m ittee w hich accepted program of bu ilding and testing of a safety vehicle RSV. This ab breviation originates from full E n glish nam e - R esearch Safety Vehicle.
On the turn of the seventies and the eighties this vehicle was built (even several such vehicles in se
veral coun tries) according to foredesigns ela b o ra ted by the C om m ittee. In the RSV vehicle there was a p o ssib ility of ch an ging essen tial param eters of chassis and m otor - car body in quite a w ide range.
On the basis o f testin g such vehicle w ere e sta b li
shed later on boundary values of basic factors for steerab ility and stab ility estim ation w hich should show cars w ith favou rable properties.
There w ere m ainly perform ed steady state cir
cular test, response for steering w heel input and re- tu rn ab ility perform ance.
The first one provides im portant inform ation concerning both passenger cars and trucks (also spe
cial ones) or buses. The tests of steering w heel in
put, returnability perform ance and severe lane chan
ge m anoeuvre are m ainly applied for testing p as
senger cars.
M agnitude of steering w heel angle in steering w heel input test and returnab ility perform ance test should be m atched so as to obtain lateral accelera
tio n in steady state m o v em en t (circu la r m otion) amounting to 4±0.2 m/s2. This is requirement and stric
tly speaking limitation connected with necessity to keep lin ear driving range. Steady state should be kept during 3 s.
M easured param eters during this test, essen tial for assigned estim ation factors are: drive velo city, steering w heel angle, yaw velocity and lateral acceleration .
From steering w heel step input test one can assign several factors am ong other: steady state yaw velocity resp on se gain, yaw velocity response tim e yaw velocity peak response tim e, yaw velocity over
shooting, TB factor (i.e. product of yaw velocity peak tim e and steady state sideslip angle) and others.
The curve of yaw velocity presented in tim e func
tion m ust lie in appropriate perm issible - zone d e
fined in RSV requirem ents (see e.g. [1], [2]).
TOM 5 lipiec - sierpień 2001 r. S ia A ta rtt& itf, nr 4
D escribed test is usually utilized for other ch a
racteristic i.e. for defining car ability to autom atic return to stright drive (so called retu rn ab ility ). At the end of steady state drive on a circle driver re le ases steering w heel and car ’’d riving o u t” from cir
cular track, again perform s several am plitudes of com plex spacial vibratio ns and then after these v i
brations cease car continues straig ht drive. For ev a luation o f retu rn ab ility one assigns ratio o f the first extrem um o f yaw velocity, after releasin g steering wheel to this velocity in steady state (before re le ase). This ratio characterize dam ping ability o f ab o ve described spacial vibrations. Besides, it is being assigned “residual” value of yaw velocity, 2 s after steering wheel release and yaw angle, obtained after integration of directional angle velocity (of course from the moment of steering wheel release). For test with velocity 80 km /h residual yaw velocity cannot exce
ed ±4°/s. Curve of car angle rotation course round ver
tical axis in time function, must lie in perm issible zone defined by requirem ents for RSV.
A nalog test is being m ade at 40 km /h velocity releasing steering w heel during steady state drive on a circle. R esidual yaw velocity after 2 s since releasing steering w heel should not exceed ±2°/s value. There is also a different p erm issib le zone for directional angle.
3. Presentation of exemplary results
In this ch ap ter the results o f test o f FO RD T ransit car equipp ed w ith three sets o f tires w ill be presented.
This car is usual equipped with tires 195 R14 C dim ension. In fath er on this set w ill be m arked w ith sym bol A. D uring the tests the tw o sets tires of d i
m ension 185 R14 C w ere app lied also. The m ain difference betw een respective set of tires was in tre ad design and applied m aterial. T hese tires w ill be m arked w ith sym bols B ad C.
The inflation pressu re was 2.8 bar (both for front in rear w heels).
The runs of yaw velocity after steering w heel release during steady state drive on circle w ith 40 km/h velocity are presented in figures 1 and 2. These runs are average from several tests.
Fig. 1. The average runs o f yaw velocity after rele
ase the steering w heel during steady state circular test w ith velocity 40 km /h - left turn
Fig. 2. The average runs o f yaw velocity a fter rele
ase the steerin g w heel during steady state circular test w ith velocity 40 km /h - right turn
The curves of yaw angle o f car w ith p e rm issi
ble zone defined by RSV requirem en ts are show ed in fig. 3 and 4.
S h M tw t& iy nr 4 lipiec - sierpień 2001 r. TOM 5
Fig. 3. The average curves o f yaw angle and R S V p e rm issib le zone a fte r release the steering w heel during steady state circular test with velocity 40 km/h - left turn
Fig. 4. The avera ge curves o f yaw angle and R S V p e rm issib le zone a fter release the steering w heel during steady state circular test with velocity 40 km/h - right turn
Fig. 5. The a verage runs o f yaw velocity a fter rele
ase the steering w heel during stea dy state circular test w ith velo city 80 km /h - left turn
Fig. 6. The average runs o f yaw velocity a fter rele
ase the steering w heel during stea dy state circular test w ith velocity 80 km /h - right turn
The tests o f re tu rn a b ility p erfo rm an ce has been also realised w ith v elocity of 80 km ph. The results analogous to show ed upper for 40 km /h are p resented in figures 5 to 8.
TOM 5 lipiec - sierpień 2001 r. S tc te tw t& U f, nr 4
Fig. 7. The average curves o f yaw angle a nd R S V p erm issib le zone a fte r release the steerin g w heel during steady state circular test with velocity 80 km/h - left turn
Fig. 8. The average curves o f yaw angle and R S V p erm issib le zone a fter release the steerin g w heel during steady state circular test with velocity 40 km/h - right turn
E valu atio n factors o f retu rn ab ility p e rfo rm a n ce assigned on basis of test results o f steering w h e
el release during steady state tests w ith 40 km /h velocity are put to g eth er in table.
Evaluation factors
lllllllll T y r a H a c i n r o ł i n nl y i c U G o i y I l d l l U I I
... ...
A B C
u 2W
p L
0.10(±0.02) 0.04(±0.02) 0.13(±0.03) 0.16(±0.05) 0.15(±0.04) 0.03(±0.02)
< M 2 )
Q
__
10.65(±0.67) -0.51 (±0.42) 1.05(±0.71) -0.94(±0.50) -1.64(±0.45) 1.62(±0.94)
U™ = ^zextr/^zO) - the ratio o f damping o f spatial vibration o f car after steering wheel release, coz(2) - residual yaw velocity after 2s from steering wheel release, P - right tum, L - left turn. In brackets - standard deviations.
3. Concluding remarks
On the basis of results presented in chap ter 2 it follow s that three various sets of tires w hich were applied for researched car have not essential in flu ence for its p roperties. S im ilar conclusions can be stated on the basis o f results of other test i.e. steady state circu lar test and steering w heel input w hich w ere also m ade during experim ents.
References
1. Rom pe K., Heissing B. Objective Testverfahren fu r die Fuhreigenschaften von Kraftfahrzeugen. Quer und Langsdynamik. Verlag TU V Rheiland GmbH, Koln 1984
2. M itschke M. D ynam ik der Kraftfahrzeuge. Band C:
Fahrverhalten, Springer Verlag Berlin, New York, 1990
3. Pieniążek W, Piotrowski B., Warszczyński J.,The Estim ation o f Tire Properties on the Basis o f Car Steerability and Stability Factors, Proceeding o f 12th Slovak Rubber Conference 2000, Puchov
4. Pieniążek W., Warszczyński J. W skaźniki kierowal
ności i stateczności samochodu jako kryteria oceny ja kości opon-możliwości, doświadczenia , Elasto
mery 2000, tom 4, nr 2-3 (21-22)
