Environmental Engineering Reference
In-Depth Information
Chapter 8
Drive system efficiency
It should not be surprising that the most important attribute of today's hybrid pro-
pulsion system is that the total driveline efficiency exceeds 80%. Given that driveline
efficiency is inclusive of electric machine(s), power converter(s), fixed gearing
and final drive. When vehicle fuel economy is in excess of 35.5 mpg in the US and
<
6.6 L/100 km in Europe as promoted in recent emission regulations, a 100Wpower
loss due to core heating in the traction motor or its attendant power inverter repre-
sents a significant impact. Weight is another very important attribute, but its impact
is negligible unless performance and economy testing includes highway grades. This
chapter provides an assessment of the complete hybrid drive system and where the
prominent loss mechanisms reside. Particular attention is paid to the traction motor-
generator (M/G) core and copper losses and the inverter conduction and switching
losses. Mechanical friction contributions are observed, particularly in regard to non-
conventional designs, because of the addition of the hybrid components.
An illustration of a non-conventional contributor to friction would be the need
for a large diameter bearing to support the otherwise cantilevered mass of a
crankshaft mounted starter-alternator. In single clutch, or M/G to transmission
torque converter arrangements, there is a tendency to have large shifts in M/G rotor
centre of gravity from the crankshaft main journal bearing and the potential to have
this rotor execute large deviations in whirl as the unsupported end has no means to
resist crankshaft bounce and whirl.
8.1 Traction motor
By and large the most significant contributor to hybrid propulsion system effi-
ciency is the electric machine. M/G losses include iron (core) losses, copper heating
(Joule heating), mechanical friction (bearing system), windage and stray losses.
Charles Proteus Steinmetz completed his doctoral work at the University of Bre-
slau, Germany, and in 1889 immigrated to the US and later joined the General
Electric Company in Schenectady, NY. In the early 1890s, Steinmetz developed
and published one of the most seminal works on the theory of magnetic hysteresis,
the phenomena in which the magnetization in a metal can have two values
depending on whether the field is increasing or decreasing. This was a major
