iVTInternational.com November 2019 51
EXISTING DRIVING CYCLES
Driving cycles currently in common
usage are designed primarily with
on-road, light vehicles in mind, but
can be modified for specialist
machinery.
New European Driving Cycle (NEDC)
The NEDC was established in 1996 as
a legal guideline for calculating the
EU standard values for vehiclespecific
fuel consumption and
emissions. This driving cycle
contains only low accelerations and
too low maximum speeds. An
unrealistically low average speed of
34 km/h reflects this. The
monotonous and repetitive sequence
of speeds allowed for easy
manipulation. In addition, altitude,
faster motorway journeys and
vehicle equipment such as air
conditioning are not taken into
account. Due to the unrealistic
measurement results, which showed
a not insignificant difference to the
actual consumption in traffic NEDC
was replaced in 2017 by the WLTP
(Worldwide Harmonized Light-Duty
Vehicles Test Procedure).
Moving to the WLTP
The aim of the globally developed
WLTP cycle was to provide an
internationally balanced test
procedure for all countries.
The scope of the driving cycle
extends primarily within the EU, but
will spread globally in modified form
in the future.
The WLTP is characterised by a
comparatively high average speed
with a high maximum speed of
131 km/h. In addition, the
acceleration level is close to reality,
which leads to high tempo
fluctuations and thus advanced the
driving cycle dynamically. The
intention behind this is to provide
a representative energy and fuel
consumption result. The new test
procedure is stricter, more detailed
and more comprehensive. The
requirements for test execution,
documentation of results and
evaluation have been increased and
expanded. The diversity of vehicle
variants, such as the scope of
equipment, is now taken into account
and must be completely tested.
Real Driving Emission (RDE)
The currently prescribed standard
6d-TEMP for vehicles requires an
extra emission test procedure, which
is to be measured under real
conditions on the road in order to
validate the laboratory results of the
WLTP. The Portable Emission
Measurement System (PEMS) is
used to measure nitrogen oxides
(NOX), particulate emissions (PN)
and carbon monoxide in RDE. There
are no standardized driving cycles
for road driving, but predetermined
boundary conditions such as road
and weather conditions or speeds
are defined.
Non-European driving cycles
Several other standardized driving
cycles exist worldwide. The Japan
Industrial Safety and Health
Association developed a transient
driving cycle called the JC08 cycle –
Japanese test Cycle (2008) –
between 2008 and 2011.
The United States Environment
Protection Agency launched the
Federal Test Procedure (FTP), in
1975-1978. In addition, there is the
Highway Fuel Economy Driving
Schedule (HWFET), which is at the
level of the specified maximum
speed of 60mph. In 2007, three
additional cycles (Supplemental
Federal Test Procedure) were added
to the existing driving cycle
inventory. The US06 high-speed
cycle, the SC03 cycle, which includes
the ancillary equipment at warm
ambient temperatures, and the
similar ‘cold cycle’ with outside
temperatures below 0°C are
components of the SFTP. The
test procedures for hybrid and
electric vehicles are individually
specified as follows:
• Battery electric vehicles
When testing electric vehicles the
battery charge level must be full at
the start of the examination. The
vehicle then runs through the driving
cycle once with a full battery and will
be reconnected to a charging station
at the end of the cycle. During this
time, an electricity meter records the
electricity consumption and energy
loss of the battery in order to
calculate the electrical range.
• Plug-in hybrid vehicles
For plug-in hybrid vehicles the cycle
is initially run with full battery
charge and after this repeated until
the battery state of charge drops to
its technical minimum. With each
repetition the combustion engine is
used proportionately higher. The last
measurement is carried out with
an empty battery, where the
combustion engine is solely the drive
power and the braking power is
applied by means of recuperation.
The multi-stage measuring
procedure not only helps to record
fuel consumption and CO2 emissions
in more detail, but also for
calculating the electrical range or
total range.
BELOW: Outline of
the non-road
transient cycle
are gaining in importance,
particularly for use in densely
populated regions. And yet there is
currently no standardized driving
cycle for industrial vehicles, but
rather test cycles for the engine test
bench in which engine speed and
torque are plotted over time.
Examples are the test cycles WHSC
(The Worldwide Reference Steady
State Cycle) and WHTC (The
Worldwide Reference Transient
Engine Cycle) as well as ESC
(European 13 mode Steady State
Cycle) and ETC (European
Transient Cycle).
The WHSC and WHTC test
procedures are internationally
harmonised test cycles in which the
vehicle engines used are tested for
their pollutant emissions in
stationary or transient condition.
The same procedure for engines is
carried out Europe-wide using the
ESC and ETC test cycles. A further
test cycle is the NRTC (Non Road
Transient Cycle), which is intended
for commercial vehicles apart from
road traffic, but these do not
represent a realistic application and
is therefore unsuitable for an
assessment basis.
Special driving cycles
The driving cycles generally used are
not suitable for off-road vehicles,
since the special requirements of this
type of vehicle differ from those of
conventional vehicles. Therefore,
a specific driving cycle is required to
make the vehicles comparable. The
driving and load profiles of such
vehicles are characterised by
comparatively low and constant
E-DRIVING CYCLES
/iVTInternational.com
