Variables considered by the model (not all variables were used for each technology) were the following:
• Vehicle load reductions:
—Tire rolling resistance, and
—Indicated (gross thermal) efficiency,
—Engine friction losses,
—Engine braking losses, and
• Transmission efficiency;
• Torque converter efficiency;
• Electric drivetrain:
—Battery storage and discharge efficiencies,
—Electric motor and generator efficiencies, and
—Charger efficiency (BEV and PHEV only);
• Fuel cell stack efficiency,
—Also the FCEV battery loop share of non-regenerative tractive energy;
• Fraction of braking energy recovered; and
• Fraction of combustion waste heat energy recovered.
Details of the input assumptions for alternative technologies and of the operation of the model are described in Appendix F.
Future costs are more difficult to assess than fuel consumption benefits. The committee examined existing cost assessments for consistency and validity. Fully learned out, high-volume production costs were developed as described in this chapter and in Appendix F.
The primary goal was to treat the cost of each technology type as equitably as possible. The vehicle size and utility were the same for all technology types. Range was the same for all vehicles except for BEVs, which were assumed to have a 100 mile real-world range. Care was taken to match the cost assumptions to the efficiency input assumptions. Results from the efficiency model were used to scale the size of the ICE, electric motor, battery, fuel cell, and hydrogen and CNG storage tanks (as applicable). Consistent assumptions of motor and battery costs were used for HEVs, PHEVs, BEVs, and FCVs. Costs were calculated separately for cars and light trucks.
For load reduction, the cost of lightweight materials, aerodynamic improvements, and reductions in tire rolling resistance were assumed to apply equally to all vehicles and technology types.
ICE technology includes a vast array of incremental engine, transmission, and drivetrain improvements. Past experience has shown that initial costs of new technologies can be high, but generally drop dramatically as packages of improvements are fully integrated over time. The incremental cost of other technologies was compared to future ICE costs (FEV, 2012).
For HEVs, costs specific to the hybrid system were added to ICE costs, and credits for smaller engines and components not needed were subtracted to arrive at the hybrid cost increment versus ICE. Similarly, the other vehicle costs were derived from ICEVs by adding and subtracting costs for various components as appropriate. Battery, motor, and power electronics costs were assessed separately for electric drive vehicles.
Many opportunities exist to reduce fuel consumption and CO2 emissions by reducing vehicle loads, as shown in Table 2.1. The load reduction portion of improved efficiency will benefit all the propulsion options by improving their fuel efficiency, reducing their energy storage requirements, and reducing the power and size of the propulsion system. This is especially important for hydrogen- and electricity-fueled vehicles because battery, fuel cell, and hydrogen storage costs are quite expensive and scale more directly with power or energy requirements than do internal combustion powertrain costs. In particular, load reduction allows a significant reduction in the size and cost of electric vehicle battery packs.
TABLE 2.1 Non-drivetrain Opportunities for Reducing Vehicle Fuel Consumption
|Light weighting||Structural materials Component materials Smart design|
|Rolling resistance||Tire materials and design Tire pressure maintenance Low-drag brakes|
|Aerodynamics||Cd (drag coefficient) reduction Frontal area reduction|
|Accessory efficiency||Air conditioning Efficient alternator Efficient lighting Electric power steering Intelligent cooling system|