73 Vehicle Architectures and Design TABLE 3.3 Battery Energy Requirements and Mass Estimates Peak Acceleration and 10-mile ZEV Range at 40 mph Urban Driving Peak Acceleration and 5-mile ZEV Range at 40 mph Urban Driving Battery Type Energy (kWh) Mass (kg) Capacity (Ah) Energy (kWh) Mass (kg) Capacity (Ah) Lead acid 3.5 94.3 11 2 47.2 5.5 NiMH 3.5 51.2 11 2 25.6 5.5 Li-ion 3.5 36.8 11 2 18.2 5.5 3.5.3.4 Generator Sizing The generator is sized to maintain series operation of the vehicle for typical urban driving condi- tions. The calculations showed that cruising at constant velocity of 40 mph with a driver and a pas- senger on a 1% grade and 10% drivetrain losses requires 12 kW.
Allowing for power to recharge the batteries, the generator can be sized to be 20 kW for the Akron hybrid vehicle. 3.5.3.5 Battery Sizing The energy required by the electric motor for initial acceleration and a minimum zero emission range with constant velocity can be used to estimate the size of the battery. The energy for initial acceleration, calculated by integrating the power required for acceleration between 0 and 9 s, is 1.62 MJ or 450 Wh. The energy required for cruising at a constant velocity of 40 mph with a driver and a passenger on a 1% grade and 10% drivetrain losses is 3 kWh for a 10-mile (15 min) battery-only range or 1.5 kWh for a 5-mile (7.5 min) battery-only range.
For a 300 V battery-pack, this requires a 10 Ah or 5 Ah battery-pack, respectively. Adding 10% margin, battery-packs with 11 Ah or 5.5 Ah can be used for 10- or 5-mile ZEV range, respectively. The estimated masses for three types of bat- tery chemistry to meet these requirements are given in Table 3.3 based on nominal energy densities. The battery-pack voltage is considered to be 300 V DC. 3.6 MASS ANALYSIS AND PACKAGING Vehicle mass budget must be evaluated during the design of a hybrid vehicle whether it is made from ground up or re-engineered from an IC engine vehicle. The vehicle fuel economy and emissions will improve as vehicle mass decreases.
Hybrids tend to be a little heavier compared to a similarly sized IC engine vehicle due to the use of both electrical and mechanical components in the powertrain. However, a good design can yield comparable masses for similarly rated hybrids and IC engine vehicles. The downsized engine in the hybrid vehicle can more than make up for the masses added due to hybridization, which includes masses for electric machines, their controllers and cooling systems and traction battery and its accessories. Mass advantages are also to be gained in hybrids by reducing fuel system sizes and removing the 12 V battery.
A mass comparison of crossover vehicles between the Chevrolet Equinox and the converted Akron hybrid is given in Table 3.4. The engine downsizing from a 3.6 L V6 gasoline engine to a 1.9 L diesel engine did not give significant mass advantage since diesel engines tend be larger and heavier than gasoline engines for comparable sizes. The exhaust system mass increased due to the addition of diesel after treatment components. The fuel tank size was reduced by 50% that pro- vided some mass savings for the hybrid. The masses of the electrical machines, controllers, trac- tion battery and thermal management systems depend on the components chosen.
The removal of the alternator and downsizing the 12 V accessories battery provided small mass savings. The cabin climate control system mass is somewhat higher for the hybrid due to the switching to an electric