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
WLTP correction algoritms
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
Norbert E. Ligterink
WLTP correction algoritms
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
Norbert E. Ligterink
WLTP correction algoritms
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
Norbert E. Ligterink
WLTP correction algoritms
Air-drag aspects air-inlet ~10%, mirror ~ 4%, ….
Norbert E. Ligterink
WLTP correction algoritms
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
Norbert E. Ligterink
WLTP correction algoritms
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%”)
Norbert E. Ligterink
WLTP correction algoritms
separate inertia
tests are performed
Wheel alignment (toe-in) expected effect ~ 3% of F0 at 0.2o (a nominal value)
Norbert E. Ligterink
WLTP correction algoritms
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?
Norbert E. Ligterink
WLTP correction algoritms
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
Norbert E. Ligterink
WLTP correction algoritms
wind measurements 5 m/s wind 6% correction on WLTC air drag
Norbert E. Ligterink
WLTP correction algoritms
wind profile (linking stations with conditions) low wind velocity near the ground
Norbert E. Ligterink
WLTP correction algoritms
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
Norbert E. Ligterink
WLTP correction algoritms
Norbert E. Ligterink
WLTP correction algoritms
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
Norbert E. Ligterink
WLTP correction algoritms
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
Norbert E. Ligterink
WLTP correction algoritms
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
Norbert E. Ligterink
WLTP correction algoritms
correction algorithms under development and validation planned