Lightweight Electric/Hybrid Vehicle Design

TRAVEL ELECTRIFIED, %
80
70
60
STRATEGY OF USE
MAXIMUM USE
50 EV OR HV
PREFERENCE
40
MAXIMUM USE
30
EV OR HV
PREFERENCE
(a)
0
0 20 30 40 50 70 100
ELECTRIC RANGE, miles
200
EV
HV
HV
EV
PRIMARY
STORAGE
PRIMARY
ENERGY
TRANSFER
DEVICE
Hybrid vehicle design 145
6.2.2 JUSTIFYING HYBRID DRIVE, FIG. 6.4
Studies carried out at the General Research Corporation in California, where legislation on zero
emission vehicles is hotly contested, have shown that the 160 km range electric car could electrify
some 80% of urban travel based on the average range requirements of city households, (a). It is
unlikely, however, that a driver would take trips such that the full range of electric cars could be
totally used before switching to the IC engine car for the remainder of the day’s travel. This does
not arise with a hybrid car whose entire electric range could be utilized before switching and it has
been estimated that with similar electric range such a vehicle would cover 96% of urban travel
requirements. In two or more car households, the second (and more) car could meet 100% of
urban demand, if of the hybrid drive type.
Because of the system complexities of hybrid-drive vehicles, computer techniques have been
developed to optimize the operating strategies. Ford researchers3 , as well as studying series and
parallel systems, have also examined the combined series/parallel one shown at (b). The complexity
of the analysis is shown by the fact that in one system, having four clutches, there are 16 possible
configurations depending on state of engagement. They also differentiated between types with
and without wall-plug re-energization of the batteries between trips.
6.2.3 MIXED HYBRID-DRIVE CONFIGURATIONS
Coauthor Ron Hodkinson argues that while initially parallel and series hybrid-drive configurations
were seen as possible contenders (parallel for small vehicles and series for larger ones) it has been
found in building ‘real world’ vehicles that a mixture of the two is needed. For cars a mainly
parallel layout is required with a small series element. The latter is required in case the vehicle
becomes stationary for a long time in a traffic jam to make sure the traction battery always remains
charged to sustain the ‘hotel loads’ (air conditioning etc.) on the vehicle’s electrical system. Cars
like the Toyota Prius have 3–4 kW series capability but detail configuration of the system as a
Fig. 6.4 Justifying the hybrid: (a) EV traffic
potential; (b) combined series–parallel mode.
PRIMARY TO
SECONDARY
DEVICE
(b)
PRIMARY CLUTCH
(P)
SERIES
CLUTCH
PRIMARY
TRANSMISSION
SECONDARY
CLUTCH
(C)
(S)
TIME
LOSS
Σ 2
DRIVE
CLUTCH
Σ1 (D)
SECONDARY
TRANSMISSION
SECONDARY
ENERGY
TRANSFER
DEVICE
Σ 3
SECONDARY
STORAGE
AUX
LOSS