Tire testing at real driving conditions andatt theth testt t standt dIntelligent Tire Technology
26 – 28 September 2011 Darmstadt

7. Intelligent Tire TechnologyContent••••••

Motivation
Measurement Equipment
Approach
Test description
Results
Conclusions

7. Intelligent Tire Technology

Motivation
••
•
•
•
•

The demand to higher efficiency concerns each component of futurevehicles
ehiclesTire resistance is one of the areas for efficiency improvements
independent of vehicle drive concepts
Understanding the behavior in real road conditions will become
more important
Standard testing methods (drum based) do not deliver roadcondition related information
Tire resistance value is relative low
Real road conditions measurement was suffering from:– Accurate measurement equipment for the forces– Ability
Abili to separate different
diffinfluence
i flsources– Low repeatability

7. Intelligent Tire Technology

Measurement Equipment on Road
• Vehicle measurement System (VMS)– Wheel Force Sensor(WFS)– Wheel Position Sensor (WPS)– Other sensors such as GPS– Vehicle ECUInformation

7. Intelligent Tire Technology

Rig Measurement Equipment• Flat belt tire testing rig (steel belt)
 Best simulation of the road• Test is performed with the same sensor used for the vehicle testing

Rig Specification
Velocity

0~200km/h

Slip Angle±20deg（0~3Hz）

Camber Angleg±15deg（0~1Hz）g

Up & Down

0~50mm（0~25Hz）

Load

Fx: ±10 kN
Fy: ± 10 kN
Fz: 12 kN

Flatness of the steel belt
(under load condition)Less than 10 μm

Bearing under the belt

Air bearing

7. Intelligent Tire Technology

Wheel Force Sensor （WFS)
6 component iin wheel
h l fforce sensor maini propertiesi• 3 axis of force and 3 axis of moment• 0.1% Resolution– 6N or 1.8Nm• Capacity:– Fx = 24KN, Fy = 15KN, Fz = 24KN
– Mx= 4.5 KNm, My =4 KNm,
Mz = 4.5KNm
4 5KNm• Data acquisition up to 1kHz
• Lightweight 3.2 Kg

7. Intelligent Tire Technology

Unique Force Detection Method•

Model Based Sensor concept•

Shared force detection method– Eight bridges are applied to the spring element– No direct detection of each component– Components are re-composed by model based calculation usingreall timeicalculationl l i DSP platform
l f– Digital conversion of all signals
and electronically rere-composing
composingovercomes disadvantages ofanalogue approach– Cross talk error can be canceledout

7. Intelligent Tire Technology

Di stributed
force bridge

High speed
A/DHigh speed
DSP

Minimized Temperature effects• Vehicle measurement is a challenge for the temperature influence– Temperature gradient e.g. break side outside– Quick change of temperature depending on driving maneuver• Robust design against Temperature effects– Share Force method allows to place the strain gauges very close toeach other
T: High– Total gradient on each gauges is very small– Small temperature effect on themeasurement
4 elements– At the same time robustness againstgauge
dynamic temperature changes

T: Low
7. Intelligent Tire Technology

Mechanical and Electrical sensitivity
••
•

•

•

Stiff sensor design for high accuracy
Sensor sensitivity:– Mechanical sensitivity x electrical sensitivity
Stiff Spring element design– Increase of robustness– Increase of eigenfrequency– Reduction of mechanical sensitivity
Increase electrical sensitivity– High precision A/D/ converting off nV order A/D/ conversion– Low noise design from less analog circuit– Optimized temperature compensation from gauge layout
The combination of all technology results in a high accurate sensor
with 1/4000 resolution

7. Intelligent Tire Technology

Wheel Force Sensor Configuration

7. Intelligent Tire Technology

Tire Loss Theory• Tire loss can be calculated from measured
parameterston theth wheelh l• Measurement parameters• Tire rolling inertia

Jt in kg・m
kg m2

• Tire effective radius

rt in mDriven WheelTire• Wheel torque My in Nm• Tire longitudinal force Fx in N
• Tire Angular speed

ω in rad/s• Tire Angular acceleration

ώ rad/s2• Calculated parameter• Tire loss (rolling resistance) Rx in NRxMy  Jt  

7. Intelligent Tire Technologyrt

 FxMyFxRx

Parameter determination: Wheel inertia• Tire rolling inertia is premeasured
using free load rotating wheel inacceleration and deceleration
condition•

M
Measurementt items
it– Tire angular speed ω [rad/s]– Angular acceleration ώ [rad/s2]– Wheel torque Myfree [Nm]•Rolling inertia formula:My freeJt ［kg・m2］


7. Intelligent Tire TechnologyTTorqueVs.
V AngularAl accelerationl ti

Testing procedure on the test track• Target: Determine “Tire Loss” from real driving condition• Test car: BMW Mini Cooper SStop
St tStart• Test Track:- East straight line: 550m
- West straight line: 554m

• Driving Maneuver:– Cost down at East straight line
– TestT t laps:
l10 llaps•100Hz data acquisition

7. Intelligent Tire Technology

Coast doCown– Acceleration at west straight lineAcceleeration- Total length: 1,792m

Test Track Measurement Results• Example plot of one round• Fx shows mainly difference
ff
between front and rear wheel• Fz shows change
g between
left and right

Coast Down

Acceleration
Stop

70s

60s

0s
10s

50s

Bank20s40s
30s

7. Intelligent Tire TechnologyStartBump

Angular acceleration determination
70s• Tire angular speed is measured from sensor
angle encoder.
• Tire angular acceleration is calculated fromangularl speed
d signalilbby titime dderivativei ti• Measurement item:– Tire angular speed
ω [rad/s]– Tire angular acceleration dωrad / s 2dt

7. Intelligent Tire Technology



60s

0s
１0s

50s

20s
40s
30s

Tire radius determination• Tire mean radius is calculated from vehicle velocity and tire angularspeed.
d• Vehicle velocity is measured from optical Doppler sensor• Instant tire mean radius is measured.
• Measurement items– Vehicle velocity against
road Vph [m/s]– TireTi angularl speeddω [rad/s]• Tire radius formula(Not considering tire slip)

rt Vph［m］

7. Intelligent Tire Technology

Measurement parameter: Wheel torqueand longitudinal force• WheelWh l torque M
My anddlongitudinal force Fx aremeasured from 6 componentsof the Wheel Force Sensor(WFS)

70s

60s

0s
10s

50s

20s
40s
30s

7. Intelligent Tire Technology

Tire Loss determination (Rolling Resistance)• To avoid tire slip error, driven
wheel data is evaluated• 10 laps of data
• To avoid some high frequency
noise a low pass filter (4 Hz) isapplied to the measurement data

Rx My  Jt  rt70s

60s

0s
10s

50s

20s
40s
30s

7. Intelligent Tire Technology Fx

Rear Left Wheel results• Average Rx: Rx = -76.1N (Acceleration), Rx = -72.8N (Cost down)• 10 laps data variation 3σ : 2.8N
2 8N (Acceleration)(Acceleration), 33.6N
6N (Cost down)• Rx for Acceleration and Rx for Cost down data are very close to each other: 3.3N

Acceleration

Bump
Coast Down

Acceleration

7. Intelligent Tire Technology

Coast Down

Rear Right Wheel results• Average Rx: Rx = -87.6N (Acceleration). Rx = -82.6N (Cost down)• 10 laps data variation 3σ: 2.5N (Acceleration)., 6.6N (Cost down)• Rx for Acceleration and Rx for Cost down data are very close to each other: 5.0N

Acceleration

Bump

Acceleration

7. Intelligent Tire Technology

Coast Down

Coast Down

Measurement result :Test rig• Test condition• Slip angle :0 [deg]• Camber angle: 0 [deg]• Wheel driven by steel belt
• Vertical load Fz: 1kN,, 2kN,, 5kN• Static velocity: 5km/h, 10km/h,20km/h, 60km/h, 80km/h, 120km/h• Rolling resistance is directly measuredfrom Fx• Rolling resistance is proportional to thevertical load and is not a function ofvelocity• Rolling resistance at 2.7kN is 42N

7. Intelligent Tire Technology

Comparison: Real road vs Test rig
Real road rolling resistance :• Rx(Left)= 74 N• Rx(Right)= 82 N
Test rig:• Rx = 42 N
Reasons for the difference:• Tire alignment• Road surface condition• Environment conditions– Wind force
fto tire– Temperature• Measurement errors– TireTi effective
ff ti radiusdi measurementt

7. Intelligent Tire Technology

Conclusion• A&D Sensor delivers highg qqualityy data
• It was possible to measure the tire loss (rolling resistance) during real drivingcondition• Great match on the measurement though 10 laps of data
• Rolling resistance measurement result is depending on driving conditions• There is a different between acceleration and cost down conditions• Useful measurement for analyzing energy loss value at real driving condition• ThereTh
are differences
diffb
betweent
roadd andd ttestt rig
i resultslt

7. Intelligent Tire Technology

Thank you for your attention!

7. Intelligent Tire Technology