Advanced Automotive Technology: Visions of a Super-Efficient Family Car

Hence, an electrical motor power output of 50 kW (or 67 HP) per ton of vehicle weight provides
comparable or average performance. Typically, electrical motors (and their controllers) weigh
about 1.0 to 1.2 kg for each kW of output so that a MMOTOR/MEV ratio of 0.05 provides a
reasonable approximation of motor weight to vehicle weight.

The weight-compounding effect is best illustrated by the ratio of battery weight to “zero weight

engine” body weight, which is a constant for a car of a given design and size. Using the above

relationship, it can be shown that:

for an acceptable performance car. This relationship is very useful in illustrating the effects

different specific energy storage capability and the choice of vehicle range on battery weight.

of

Table A-2 lists the actual and specific energy consumption of several recent EV models, based

on the city cycle test procedure. The energy consumption values for these EVs indicate that the

specific traction energy E is similar across most cars ranging between 0.084 to 0.151 kWh/ton-km

or 0.12 to 0.22 kWh/ton-mile. Vehicles at the high end of the spectrum were models with low

regenerative braking efficiency or with less efficient motor/electronics, but the body

characteristics or total weight did not have a significant impact on the specific energy efficiency.

(For example, the GM Impact is slightly less efficient than the Cocconi CRX-4 using this

measure). The Cocconi CRX stands out with an energy consumption of 0.084 kWh/mi but it has

no accessories, not even power steering. These energy consumption figures are based on federal

city cycle driving, and are often not the ones quoted in the press.

Many publications also provide inconsistent and in many instances, significantly lower estimates

of energy used for each ton-mile, based on the same cars shown in table A-2. For example, ARB

tests of the Cocconi CRX were used to derive energy from the battery used as 96.5 Wh/km, but

this is based on subtracting all of the regenerative energy going into the battery from the battery

output^18 ; this is incorrect because not all of the regenerative power going in can be recovered

owing to charge/discharge loss in the battery. The GM Impact is another car where city cycle

energy consumption has been reported as low as 0.065 kWh/km.^19 However, GM claims a range

of 70 miles in the city based on the discharge of a 16.3 kWh battery to 80 percent DoD.^20 If 13

kWh (0.8x 16.3) is required to travel 70 miles (112.6 km), it is easy to see that the quoted 0.065

kWh/km cannot be correct. Finally, it should be noted that E is calculated in Wh/km per kg of