Hybrid vehicle characterization - Propulsion Systems for Hybrid Vehicles - page 429

9.3 Combined cycle

The US-combined cycle for gasoline (or diesel) is the weighted average of city and
highway fuel economy according to (9.1). Depending on vehicle electric fraction
and requirements for electric-only range, there are additional weighting functions
used by industry to quantify the vehicles combined fuel economy. Typical weights
are utility factor (UF) derived from the US National Transportation Survey, 1995,
and the mileage weighted probability (MWP):

1
ð 0 : 55 = FE city Þþð 0 : 45 = FE hwy Þ

FE US comb ¼ (mpg) ð 9 : 1 Þ

In vehicles for which electric range is possible owing to substantial electric
storage capacity, either the UF or the MWP method is used. More details can be
found in the report by Graham [10].
UF weighted

1
ð UF city FCT city = 33 : 44 Þþð 1 UF city = PCT city Þ

FEUF city ¼ ð mpeg Þ ð 9 : 2 Þ

where UF city and UF hwy are the utility factors for a given value of electric-only
range (e.g. Reference 10, Figure B.1), FCT is the economy obtained during full
charge testing and PCT is the economy obtained at partial charge testing. A factor
of 33.44 kWh/equivalent gallon of gasoline is used to convert electric-only range
'fuel' to gasoline for fuel economy predictions, or mileage per equivalent (US)
gallon (mpeg):

1
(UF hwy FCT hwy = 33 : 44 Þþð 1 UF hwy = PCT hwy Þ

FEUF hwy ¼ ð mpeg Þ

ð 9 : 3 Þ

1
ð 0 : 55 = FEUF city Þþð 0 : 45 = FEUF hwy Þ

FEUF comb ¼ ð mpeg Þ ð 9 : 4 Þ

MWP weighted
MWP computation of combined mode fuel economy in the case of vehicles having
electric-only range is again computed using the appropriate definitions from
Reference 10. The conversion factor of 33.44 kWh/equivalent gallon of gasoline is
used:

1
ð MWP city FCT city = 33 : 44 Þþ½ð 1 MWP city Þ= PCT city

FEMWP city ¼ ð mpeg Þ

ð 9 : 5 Þ