Introduction to Alternative Vehicles and Design Fundamentals

Compelling Impetus for Alternative Vehicles

• Environmental Concerns: The primary driver for alternative vehicle development is urban pollution caused by Internal Combustion Engine Vehicles (ICEVs), which release exhaust emissions that contribute to the greenhouse effect and global warming.

• Economic and Political Implications: The world is currently dependent on oil as the sole energy source for passenger vehicles. Diminishing global oil reserves create an economic crisis that is expected to become acute as reserves decrease. This dependence also carries significant political ramifications.

• Pollution Concentration and Scoping: While ICEVs scatter emissions wherever they are driven, power generation for electric vehicles (EVs) occurs at localized plants. These are easier to regulate and are typically located outside urban areas, reducing direct human exposure to pollutants in cities.

• Renewable Energy Integration: Electric power can be generated via renewable sources, including water (hydroelectric), wind, and solar energy, representing the most environmentally friendly approach to transportation.

• Off-Road Applications: Advantages of alternative transportation technologies extend to industrial and commercial off-road vehicles, offering clean and efficient performance in non-passenger sectors.

Evolution and History of Electric and Hybrid Vehicles

• Early Dominance (Prior to 1900s): Electric vehicles appeared in the mid-nineteenth century, predating gasoline vehicles.

  • In 1900, 4,200 automobiles were sold with the following market share: 40% steam powered, 38% electric powered, and 22% gasoline powered.

• Factors of Disappearance (Early 1900s):

  • The invention of the starter motor in 1911 made gasoline vehicles easier to start (removing the need for hand-cranking).

  • Improvements in mass production, specifically by Henry Ford, dropped the price of the Model T from $850.00$ in 1909 to $260.00$ in 1925.

  • Lack of electricity in rural areas made battery charging inconvenient compared to the availability of gasoline.

• Resurgence and Developmental Milestones:

  • 1960s: Interest renewed due to environmental hazards and oil dependence. General Motors (GM) initiated a $15\text{ million}$ program.

  • 1968: "The Great Electric Car Race," a $3,300\text{ mi}$ cross-country competition between Caltech and MIT, stimulated public interest.

  • 1970s: The 1973 Arab oil embargo increased demand for alternatives. In 1976, Public Law 94-413 (Electric and Hybrid Vehicle Research, Development and Demonstration Act) was enacted.

  • 1990s: Legislative mandates, such as the California Air Resources Board (CARB) ruling in 1990, required 2% of sales to be zero-emission vehicles (ZEVs) by 1998, rising to 10% by 2003.

  • Recent Progress: Toyota released the Prius in 1999. Tesla Motors delivered the Roadster in 2008, the first production vehicle utilizing Li-ion technology and achieving a range over $200\text{ mi}$.

System Definitions and Architectures

• Electric Vehicles (EV): Defined by two primary features:

  1. The energy source is portable and electrochemical or electromechanical.

  2. Traction effort is supplied only by an electric motor.

• Hybrid Electric Vehicles (HEV): As defined by the International Electrotechnical Commission (Technical Committee 69), these vehicles utilize propulsion energy from two or more kinds of energy stores or converters, with at least one store/converter on board (e.g., ICE engine + electric machines).

• Fuel Cell Electric Vehicles (FCEV): Utilize a fuel cell to convert chemical energy (hydrogen) directly into electrical energy without combustion. These are categorized as ZEVs if pure hydrogen is used.

• Powertrain Components:

  • Energy Storage: Includes battery-packs, ultracapacitors, or flywheels.

  • Electric Drive: Comprised of power electronic devices and electronic controllers to manage conversion of steady DC voltages into variable voltage supplies.

  • Vehicle Supervisory Controller (VSC): The "brain" of the vehicle that coordinates multiple energy conversion devices and transmission paths (electrical and mechanical) using the Controller Area Network (CAN) protocol.

  • DC-DC Converter: Manages power conversion between different voltage levels (e.g., high-voltage battery to low-voltage auxiliary systems).

Mechanical and Electrical Transmission Paths

• Mechanical Power Transmission Path (MPTP): Consists of the engine, transmission, and coupling devices (differential/final drive) delivering power to the wheels via a driveshaft.

• Electrical Power Transmission Path (EPTP): Consists of energy storage, power converters, electric machines (motors/generators), and coupling devices. Power flow in this path is bidirectional, allowing for regenerative braking.

• Hybrid Configurations:

  • Series: The engine drives a generator to provide electricity for the motor; there is no mechanical link between the engine and wheels.

  • Parallel: Both the engine and the electric motor can provide propulsion power to the wheels simultaneously or independently.

  • Series-Parallel: A combination that allows the engine to either drive the wheels or charge the energy storage via a generator.

  • Charge-Sustaining Hybrids: Vehicles that do not require plugging in; all energy is derived from stored fuel processed through the engine.

Vehicle Mass Dynamics and Design Calculations

• Mass Definitions:

  • Curb Mass ($m_v$): Total mass with standard equipment and full fluids, excluding passengers/cargo.

  • Gross Vehicle Mass ($m_{gv}$): Curb mass plus passengers and cargo.

  • Sprung Mass: Fraction of curb mass supported by the suspension.

  • Unsprung Mass: Fraction carried by the wheels and moving with them (e.g., hub motors, calipers).

• Mass Distribution and Balance:

  • Front longitudinal length ($a$) is the distance from the front axle to the center of gravity; rear longitudinal length ($b$) is from the rear axle to the center of gravity. Total length is $l$.

  • Front vehicle mass: $m_{vf} = m_v \times \frac{b}{l}$

  • Rear vehicle mass: $m_{vr} = m_v \times \frac{a}{l}$

  • Ideal front-to-rear distribution: $60:40$ or less. Ideal sprung-to-unsprung ratio: $10:1$.

• Equivalent Mass ($m_{eq}$): Incorporates the inertia of rotating components for design calculations.

  • $m_{eq} = k_m m_v + N_p m_p$

  • Dimensionless mass factor ($k_m$): $k_m = 1 + \frac{4 J_w}{m_v r^2_{wh}} + \frac{J_{eng} \xi^2_{eng} \xi^2_{FD}}{m_v r^2_{wh}} + \frac{J_{em} \xi^2_{em} \xi^2_{FD}}{m_v r^2_{wh}}$

  • Where $J_w$, $J_{eng}$, and $J_{em}$ are the inertias of the wheels, engine, and electric machine; $\xi$ represents gear ratios.

Electric Motor and Engine Performance Ratings

• Continuous vs. Peak Power: An electric motor is rated based on what it can deliver continuously without overheating, but can provide $200\%$–$300\%$ of this rated power for short bursts.

• Torque Characteristics: Electric motors provide maximum torque at zero speed (stall conditions). In contrast, IC engines produce no torque below a minimum speed and require a transmission to match narrow high-power ranges with vehicle speed.

• Power-Torque Relationships:

  • $\text{Power (W)} = \text{Torque (Nm)} \times \text{Speed (rad/s)}$

  • $\text{hp} = \frac{\text{Torque (ft}\cdot\text{lb)} \times \text{rpm}}{5252}$

• Motor Design Requirements:

  • High torque-to-inertia ratio ($T_e/J$) for acceleration.

  • High power-to-weight ratio ($P_e/w$).

  • Extended constant power regions and ruggedness.

Well-to-Wheel (WTW) Efficiency Analysis

• Concept: WTW efficiency measures overall efficiency from raw fuel extraction to energy at the wheels. It is the product of Well-to-Tank (WTT) and Tank-to-Wheel (TTW) efficiencies: $\text{WTW} = \text{WTT} \times \text{TTW}$.

• Efficiency Comparison (Standard Data):

  • ICEV: TTW is approx. 25%. Overall WTW is low due to engine losses.

  • HEV: TTW is approx. 50% due to engine downsizing and optimization.

  • Battery EV: TTW is high ($80\%$–$90\%$), but overall WTW is limited by the WTT efficiency of the electrical grid (energy generation from coal/oil).

• GREET Model Data (Targeting Mid-size Sedan):

  • SI ICEV: WTW Efficiency = 17.41%.

  • Battery EV: WTW Efficiency = 18.43%.

  • Plug-In SI HEV: WTW Efficiency = 15.29%.

• Pollution Impact (100% Electrification Claims):

  • Carbon dioxide cut by half.

  • Nitrogen oxides cut slightly based on utility standards.

  • Sulfur dioxide linked to acid rain may increase slightly unless power plant standards are tightened.

  • Drastic reduction in smog and ozone depletion.

Summary of Case Studies and Vehicle Specifications

• GM Electrovair II (1966): $115\text{ hp}$ induction motor, $13,000\text{ rpm}$, silver-zinc ($Ag\text{-}Zn$) $512\text{ V}$ battery, top speed $80\text{ mi/h}$, range $40\text{--}80\text{ mi}$, weight $3,400\text{ lb}$.

• Saturn EV1 (1995): Leased in CA and AZ for approx. $30,000$, range $70\text{--}90\text{ mi}$, acceleration $0\text{--}60\text{ mi}$ in $8.5\text{ s}$, consumption $30\text{ kWh/100mi}$ city.

• Tesla Roadster (2008): $53\text{ kWh}$ Li-ion pack ($6,831$ cells), nominal voltage $375\text{ V}$, range $244\text{ mi}$, $215\text{ kW}$ induction motor, $400\text{ Nm}$ peak torque, gearbox ratio $8.28:1$.

• Honda FCX Clarity: Hybrid fuel cell/battery, $100\text{ kW}$ PEM fuel cell, $288\text{ V}$ Li-ion battery, $100\text{ kW}$ motor, fuel economy $74\text{ mi/gge}$ ($gge$ = gasoline gallon equivalent).

• Toyota FCHV-adv: Based on Highlander, range $431\text{ mi}$, economy $68.3\text{ mi/kg}$.

Market Constraints and Infrastructure

• Impediments: Limited range, high initial cost of battery replaces, and lack of mature infrastructure (standardized plugs, cords, and charging stations).

• Electricity Generation Profile: US electricity is generated from Coal (54%), Nuclear & Renewable (33%), Gas (9%), and Oil (4%). This highlights that EVs primarily shift energy consumption from imported oil to domestic coal and gas.

• Engineering Job Prospects: Increased EV demand expands roles in power electronics, power generation resources, packaging/thermal management, and infrastructure development.