MAE 442 Automotive Engineering: Hybrids

MAE 442 Automotive Engineering:Hybrids Ewan Pritchard, PE October 5th, 2009

Hybrid Definition • A hybrid is a combination of two things • In this case we mean a vehicle powered by two different power plants • Electric motor • Internal combustion engine

Is a Hybrid Vehicle a New Idea? • Hybrids existed in the late 1800’s • Cars could be fuelled by either electric or ethanol • No regenerative energy • The invention of the IGBTbetween 1960 and 1990made way for the modernhybrid electric

The Modern Hybrid • Does not idle when stopped • Uses a battery pack to store energy • Uses an electric motor to accelerate • Recharges batteries when braking or coasting • Allows for a smaller gasoline engine • Increased fuel economy, lower emissions, and lower engine wear

Why Hybrid: Fuel Economy • As fuel prices rise – so does the drive to improve fuel economy • Reduced Dependence on Foreign Fuel • Fossil fuels are not sustainable – it took millions of years to make them, and about 300 years to consume them.

Why Hybrid: Emissions • Environmental issues • NOx – nitrogen oxides • Works with sunlight to form ozone (lung damage) • Forms nitric acid in the air (acid rain) • Enters the upper atmosphere and causes a greenhouse effect. (Global warming & climate change) • CO2 – carbon dioxide • Enters the upper atmosphere and causes a greenhouse effect. (Global warming & climate change)

Why Hybrid: Emissions • Environmental issues • Particulate Matter • PM10 – 10 microns in size, particulates enter the upper respiratory system and cause congestion, smaller particles cause lung damage. • PM2.5 – 2.5 microns in size, passes through the alveoli in the lungs and enters the bloodstream to cause pulmonary distress

Why Hybrid: Performance A tale of two drivelines – both 102 kW (137 HP)

Conventional versus Hybrid Design • Conventional Design Characteristics: • Total Power (Top Speed) • ¼ mile time • 0-60 • Modern Design Characteristics: • Pep (acceleration at particular speeds) • Fuel economy on a specific drive cycle • Ability to meet trace • Minimized emissions on that cycle

Drive Cycle • Hybrids and Plug-In hybrids add new dimensions to a historically single dimension problem

Where the Power Goes

A Hybrid Electric System Can Help Minimize These Losses • Engine losses • Standby/idle losses • Driveline losses • Braking losses • Electric accessories

Engine Losses and Idling ~80% of Total Losses • An engine will typically run at many different efficiencies • This engine could run at 44% efficient • It will likely average at about 18% • By eliminating idling and low torque, the average could be easily running over 30%

Driveline Losses~5.6% of Total Losses • Hybrid drivelines can be applied in several ways, one possibility (series hybrid) can eliminate the driveline completely, eliminating this loss Conventional All Electric

Driveline Losses~5.6% of Total Losses • In a series driveline, only an electric motor is connected to the drive wheels • In a parallel system, both the gasoline and the electric motor are connected to the drive wheels Series Parallel

Braking Losses and Inertia ~5.8% of Total Losses • A hybrid vehicle can significantly reduce braking losses by recapturing the energy electrically in a generator • This also significantly reduces brake wear • The vehicle is also slowed while traveling down hills by regeneration

Auxiliary and Accessory Loads~2.2% of Total Losses • Includes fans, pumps, compressors and alternator • When these are belt driven, they are subject to the current engine speed, which can range from 800 RPM up to 6000 RPM • At varying speeds these accessories are typically VERY inefficient • Each of these is moving towards electrically driven components due to the inherently higher efficiency of electric motors

Hybrid and Electric Vehicle Components • All hybrid and electric vehicles have 4 basic components. • Electric Motor • Controller/Inverter/Drive • Batteries • Logic • Improvements in high power electronics, materials and computing capacity have led to significant changes in the past 20 years.

INDUCTIONMOTOR COMPONENTS • Rotating components • [1] Shaft • [2] Rotor • [3] Rotor fins • [4] Fan [1] [2] [3] [4]

INDUCTIONMOTOR COMPONENTS • Housing components • [5] End bells / bearing housings • [6] Stator housing • [7] Cooling fins • [8] Junction box • [9] Fan shroud [5] [7] [6] [8] [9]

INDUCTIONMOTOR COMPONENTS • Fixed components • [10] Seals • [11] Stator windings • [12] Core iron / lamination stack • [13] Bearings [10] [11] [12] [13]

Components: Electric Motor - DC Graphic courtesy of SMMA | www.smma.org

Components: Electric Motor - AC Graphic courtesy of SMMA | www.smma.org

Components: Electric Motor - Controlled Graphic courtesy of SMMA | www.smma.org

Controller • Converts Battery DC to a chopped DC power • Can chop in amplitude (DC) or frequency (AC) • Power is based on low voltage input signal • 4-20 mA or 0-5V • In other fields this is called a drive or inverter • Variable Frequency (AC) • Pulse Width Modulation (AC) • Buck Conversion (Reduce - DC) • Boost Conversion (Increase - DC)

Batteries • Batteries rule the performance of the vehicle • They dictate how much power you get (kW) • They dictate how much energy you get (kWh) • A single cell dictates the battery voltage each cell mates two dissimilar materials • Lead Acid (2.1 V) • Nickel Cadmium (1.2 V) • Nickel-Metal Hydride (1.2 V) • Lithium-Ion (3.7 V) Anode (+)CathodeElectrolyte Pb PbO2 KOH NiOOH Ni H2SO4 NiOOH AB5 * KOH LiC6 Li2FePO4F LiPF6 * AB5 is a combination of (A) rare earth mixture and (B) Zirconium or Nickel

Batteries: Packaging • Cylindrical • Prismatic • Button • Pouch Source: www.batteryuniversity.com

Batteries (section 12.1.2) • State of Charge (SOC) • Measured as a percentage of total battery energy (0-100%) • Typically should not go below 20% • Depth of Discharge (DoD) • Inverse of SOC • Power (kW) • Energy (kWh) The 18650 cell is proving to be common for hybrids. Similar to a AA cell, the dimensions are 18mm in diameter and 650mm in length.

Batteries: Basic Characteristics • A-h • Typically used for power batteries • Cells often described in mA-h • C Rate • A normalized rate of power use to qualify testing • 100% discharge divided by the time in hours • C2 means the discharge rate was 100% in ½ hour • C/2 means the rate was less aggressive – over 2 hours • Cycle Life • Always measured based on DoD • Ex. 1000 cycles at 80% DoD • Weight/Volume • Measures in terms of • W/kg and W-h/kg • W/l and W-h/l

Cycle Life Source: Duvall, EPRI Study of cycle life versus depth of discharge

Energy Densities Source: www.batteryuniversity.com

Ragone Plot Source: Lawrence Berkeley National Labs

MAE 442 Automotive Engineering: Hybrids