coast-down test and the corresponding real-world rolling ... · (variable) test conditions real world conditions correcting for the differences variations in vehicle models weight

WLTP correction algoritms

coast-down test and the corresponding real-world rolling resistance, air-drag, and inertia Norbert E. Ligterink

(variable) test conditions real world conditions correcting for the differences

variations in vehicle models

weight and options

wheels and tyres

maintenance and settings

variations in test circumstances

road surface

road gradient

altitude

ambient conditions

temperature

wind

humidity

Norbert E. Ligterink


possible purposes:

• correct road load values with test conditions*

• correct test result with real-world conditions*

• improve test procedure for large variations*

• improve energy label with vehicle variations

• advise customers on expected differences

* offered in the proposal

General approach: search quantify validate

coast down test yields typically ~ 5% variation between tests

challenge: less than 1% unexplained variation left after corrections

monitor, log, and analyse:

log many aspects: e.g. temperatures (road, tyres, ambient)

use multi-regression based on the expected dependencies

extra equipment:

official Dutch weather station at the location, extra weather station,

extra wind meter, (contact) temperature sensor

scales (weight per wheel)

pressure meter



Some major aspects of coast-down tests

vehicle

air-drag

rolling resistance

inertia

wheel alignment

test protocol

warming up

ambient

wind

temperature

track

slope

road surface



Vehicle

air-drag

vehicle model options

movable parts

wheels

rolling resistance

tyre width

tyre label

tyre pressure

inertia

wheel interia

wheel alignment

toe-in/camber/caster



Air-drag aspects air-inlet ~10%, mirror ~ 4%, ….



Testing with open air-inlet as reference, but also testing with closed inlet.

Monitoring on-road inlet variations is under consideration.

tyre pressure rolling is deforming, (viscous) deforming is work



current WLTP text based on

specific 2.4 bar set pressure

tyre pressure

varies 0.2 bar

(and more) during

coast-down tests

inertia aspects: wheel and tyre ~ 60%-70% of wheel + tyre weight added (35-50 kg > “WLTP 3%”)



separate inertia

tests are performed

Wheel alignment (toe-in) expected effect ~ 3% of F0 at 0.2o (a nominal value)



test vehicle:

toe-in 0.0o – 0.4o with 0.2o nominal

rear wheels

may have

toe-in with

front-wheel

drive

camber and caster camber fixed? caster irrelevant for coast down?



dynamics not relevant for coast down, but likely for on-road forces (bends, undulation, etc.).

Ambient

wind

location

height

gustiness

temperature

air density

air viscosity

vehicle (lubricants?)

air pressure (altitude, meteorology)

air density



wind measurements 5 m/s wind 6% correction on WLTC air drag



wind profile (linking stations with conditions) low wind velocity near the ground



turbulence = gustiness, due to wind shear forces

Typical land wind speeds at 80 metres high 3-6 m/s: at lower heights about half that number or less





Dutch test location:

old airstrip with 10+ years

historical wind data

near the coast

wind speeds at 10 metres height

hopefully some nice windy days during the tests (max. ~7.0-8.0 m/s)

Ambient temperature a mixed bag of “opposite” effects: density, viscosity and turbulence



coast-down testing at higher altitudes seems always positive

trivialisations of

the “full problem”

are numerous

(including WLTP text):

most consider only

air-density effect

Test tracks and roads



Track and road properties

• road surface: rolling resistance

• road undulation: forces and vibration

• road gradient: sum of both directions

• oval or straight up-and-down

Under consideration:

• tests at 2-4 tracks

• different road surfaces

• 0.0% and 0.3% gradients

• resistance characteristics test:

• surface roughness

• surface material

Conclusions

Major effects (i.e. > 4% change possible in air drag or rolling resistance)

wind

altitude (temperature / air density)

tyre pressure

air-inlet settings

wheel choice

tyre choice

vehicle weight

wheel alignment

vehicle model options



correction algorithms under development and validation planned

Documents

coast-down test and the corresponding real-world rolling ... · (variable) test conditions real world conditions correcting for the differences variations in vehicle models weight