Transcript No Slide Title

Vehicle Efficiency Pathways
How modern passenger cars are removing themselves from the environmental debate
John Bucknell
GM Powertrain
1
Abstract
Modern passenger cars must respond to market demand and regulation forces, delivering superior air
quality, utmost safety and ever-higher energy efficiency. This lecture will discuss efficiencies on both
the supply and demand pathways for improving energy efficiency in the context of emissions and safety
regulations. Well-to-wheel and pump-to-wheel efficiencies will also be covered in brief to highlight the
efficiency of Electric Vehicles
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Topics
 Transportation Efficiency
 State of the industry
 Supply-side Efficiency
 Powertrain Efficiency
 Driveline Efficiency
 Load-leveling
 Demand-side efficiency
 Aero, rolling-resistance, inertia
 Electric Vehicles & Fuel-Cell Vehicles
 Pump-to-wheels, well-to-wheels
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Market Economics
 Cost of ownership
 Market demand has illustrated that customers will purchase what they can afford.
of ownership have great difficulty penetrating the market.
Technologies that increase cost
 Energy Costs
 Dual impact of increasing environmentalism and increasing energy costs have raised the visibility of vehicle
efficiency.
 Low energy cost of petroleum products has been the primary factor that has driven the market into a near
monoculture for it’s energy needs.
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Transportation Efficiency
 State of the industry
 Economies of scale drive allow manufacturers to compete on cost.
Any technology that cannot make a
component at a minimum rate of one per minute requires additional sets of tooling, driving up investment and
increasing the number of sales to break even.
 Profit margins in the automotive industry are exceptionally small, as you’d expect with strong competition for a
very large revenue stream.
 State of the world has changed rapidly – developing new technologies that are sufficiently robust to be used by
every consumer can take a decade or more. The industry is responding to the need for greater efficiency, vehicles
on the market today are just the beginning.
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Regulation
 Tailpipe Emissions
 Air quality has been driven by the EPA and the California Air Resources Board.
formed and regulated follow.
Details on how emittants are
 Passenger safety
 Customer awareness of impact performance on standardized tests has driven the industry to achieve a minimum
“Four star” rating in any test. The degree that of likelihood of injury to achieve the best rating has decreased
significantly over the last ten years. High strain-energy density materials, and large masses of them have driven
up body structure mass by about double in the same time frame.
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Emission and Fuel Economy Test Cycles
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Engine Fuel Balance
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Emissions Standards 1960 to 2008
History of Emission Control Standards
99.99%
Reduction
12
11
Typical 1960 Vehicle (pre-control)
10
9
HC St andard
8
7
6
5
4
3
2
0.5
1983 Federal Tier 0
0.4
1971 California Std.
1977 Federal Std.
1
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
HCStandard
NOx St andard
0.3
Federal Tier 1
0.2
0.1
NLEV
LEV2
ULEV2
0
0
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SULEV2
0.1
0.2
0.3
0.4
0.5
NOx Standard
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Exhaust Aftertreatment
Catalysts have the capability of modifying the reaction rates of chemical processes (typically increasing reaction rates) without being consumed
while doing so.
The following chemical processes are of interest in automotive exhaust catalytic aftertreatment
•
•
•
•
HC + O2 CO2 + H2O
CO + O2 CO2
NO  N2 + O2
These reactions proceed toward equilibrium at very slow rates at prevailing exhaust temperatures - catalysts increase their reaction rates
to a degree that the exhaust aftertreatment becomes practical.
Conversion efficiency: (inlet concentration - outlet concentration)/inlet concentration
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Essential Components of a Catalytic Converter
Substrate
Mat
Can
Washcoat
Catalysts
Substrate: a ceramic honeycomb-like structure with thousands of parallel channels for applications of washcoat and catalysts
Mat: Provides thermal insulation and protects against mechanical shock and chassis vibration
Can: A metal package encasing the catalyzed substrate and mat
Washcoat: a coating that increases the surface area of the substrate for catalysis
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Source: Corning (2001)
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Catalysts for Exhaust Aftertreatment
The active catalytic material is typically a blend of platinum, palladium, rhodium and nickel.
Small amounts of these materials are distributed on a alumina (Al2O3) washcoat, which is specially processed to have very high microscopic
surface area. The high washcoat surface area helps to keep the catalytic material spread out to reduce the tendency to agglomerate and thus
loose surface area.
Cerium oxide is often added to this mix to mechanically stabilize the alumina microstructure against thermal degradation.
Typically there are 0.5-2 grams of catalytic material per liter of overall catalyst volume, and the overall catalyst volume is about 50 ~ 80% of
the engine displacement, depending on the application.
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Temperature Effects on Catalyst Capabilities
Catalyst efficiency at catalyst temperatures below 200oC is extremely
low.
Catalyst efficiency rapidly increases as its temperature rises above
200oC and reaches its temperature plateau at about 400oC.
Light-off temperature: conversion efficiency reaches 50%
Current exhaust system design practice insures catalyst light-off
within ~ 20 seconds without special aids. Catalyst heating devices
in lowest emissions vehicles can achieve light-off in under 10
seconds.
Source: Heywood (1988)
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Catalyst Efficiency with Air/Fuel Ratio
Steady improvements in fuelling
control, engine-out emissions and
catalyst technology has made it
possible to achieve 100%
conversion rates of HC and NOx
after catalyst light-off.
Source: Heywood (1988)
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Emissions Summary
Fuel-burning engines create pollutants that are regulated - which
are ever-more stringent. Emissions-control technology has
evolved to the point where three-way catalysts are 100% efficient
in converting HC, NOx and CO – only if the feedgas operates
very close to stoichimetric air-fuel ratio.
Any lean-burning combustion process (Diesel or stratified charge)
which improves fuel consumption also prevents catalytic NOx
reduction by maintaining oxygen in the exhaust stream. Several
technologies are emerging which consume fuel or reductant to
purge Lean NOx Traps, at the cost of fuel consumption or added
complexity.
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Supply-Side Efficiency
Energy conversation pathway
 Powertrain Efficiency (Stratified Charge/HCCI, Downsizing/Boosting)
 Driveline Efficiency (Multi-speed Transmissions, CVTs)
 Load-leveling (stop-start, mild hybrid, series and parallel hybrids)
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Energy Distribution
in Passenger Car Engines
Source: SAE 2000-01-2902 (Ricardo)
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Modern Naturally Aspirated
Brake Thermal Efficiency Map
1
0.35
0.9
0.3
0.7
0.25
0.6
0.5
0.2
0.4
0.15
0.3
0.2
0.1
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0.55
0.6
0.05
Fraction Maximum Engine Speed
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Fraction Thermal Efficiency
Fraction Maximum Torque
0.8
Compression vs Spark Ignition
Compression ignition achieves significantly higher compression ratios than
spark ignition – raising thermal efficiency
Spark ignition engines control load by throttling, introducing parasitic
losses at less than maximum load which reduces thermal efficiency
Smoke limits reduce power density of diesel engines to only about 80% of
energy density of spark ignited of similar displacement. High operating
pressures require heavy construction which further lowers power/weight
ratio
Source: Heisler (1995)
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Powertrain Efficiency Pathways
- Engine Prior three slides show that the maximum fraction of fuel energy that reaches the brake is 30-40% of the fuel input energy, which is the most
that thermodynamics allows.
Spark ignition engines pay a loss to reduce load by throttling – which is effectively operating a vacuum pump. Several technologies seek to
reduce or eliminate pumping work:
•Exhaust Gas Recirculation (EGR) – load reduction by diluting incoming combustion air
•Variable valve timing (including cam phasers and variable lift/duration systems) – load reduction by reducing trapping efficiency and adding
residual (internal EGR)
•Stratified Charge with unthrottled operation – load control via fuel mass running lean
•Homogeneous Charge Compression Ignition (HCCI) – load control via fuel mass and residual preventing lean operation
•Downsizing/Boosting – Reduction in displacement of engine so use of lowest efficiencies is mostly avoided and then boosting to enhance
available load
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Powertrain Efficiency Pathways
- Driveline Knowing that an internal combustion engine is most efficient in a limited regime, the driveline can be optimized to enable engine operation
the least amount of time away from that regime.
•Multi-speed Transmissions – 6, 7, 8 speeds with ratio ranges from 5.0-6.0 give powertrain controller best option of matching engine to
current power demand
•Continuously Variable Transmissions – Same as multi-speed transmissions, but typically have high parasitic losses
•Load Leveling – Through use of onboard energy storage (electric or other), energy conversion can happen at most efficient point in map.
Hybrids achieve this through several different strategies – parallel, series or dual-mode are most-often discussed. Micro-hybridization also
appearing due to low cost of implementation.
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Load-Leveling
Engine Stop Start (ESS)
 Eliminates fuel consumed during deceleration and idle
Fuel
On
Fuel
Off
Source: SAE 2001-01-0326 (GM)
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Load-Leveling
Mild Hybrid
 Regenerative Braking, Load-Leveling and Idle Stop
Source: SAE 2006-01-1502 (GM)
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Load-Leveling
Strong Hybrid
 Electric-only operation, Regenerative Braking,
Load-Leveling and Idle Stop
 Parallel, Series and Two-Mode e-CVTs
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Demand-Side Efficiency
 Not a true ‘efficiency’, however losses that are not minimized could be considered ‘in-efficient’
 Major Components
Inertia Loads (Kinetic Energy)
Aerodynamics
Rolling Resistance
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Demand-Side Efficiency
 Inertia Loads
 Vehicle mass requires proportional power to accelerate.
sensitive to vehicle mass.
Vehicle duty cycles with greater time spent accelerating will be more
 Aerodynamics
 Pressure drag:
The loss due to the difference in pressure on the front face versus the rear face of the vehicle. The dynamic
pressure (also called stagnation pressure) on the leading face is a measure of the kinetic energy of the displaced air.
 Friction drag:
Losses due to viscosity effects are also substantial. Boundary layer theory says that particles immediately next to
a vehicle must be moving at vehicle speed as compared to at the free stream velocity. The shear force created by the relative
velocity of the fluid is proportional to vehicle speed and ‘wetted’ surface area moving through the fluid.
 The two speed-dependent components cause aerodynamic drag to increase primarily with the square of vehicle speed
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Demand-Side Efficiency
 Rolling-resistance
 Driveline: Seals, bearings, gears, CV and Cardon (universal) joints
 Any component using a viscous fluid to reduce contact stress for increased durability also suffers the losses
of viscous shear forces regardless of the load.
 Brakes
 Friction brakes work by rubbing two components together. Unfortunately due to the balancing of pad
retraction and response time, disc brakes will drag the pads against the rotors – a little or a lot depending
on the design. Drum brakes by their nature have very little hydraulic volume and thus can retract far
enough to not drag.
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Demand-Side Efficiency
 Rolling-resistance
 Tires
 Part of the suspension isolating the vehicle from surface irregularities. Tire is both a spring and a damper,
with greater spring rate and lesser damping force with lesser sidewall height. Spring rate is proportional to
inflation pressure. Greater isolation drives greater sidewall and lower pressure.
 Inflation pressure is same as tire contact pressure. Contact area is proportional to mass supported by the
tire. The greater the contact area, the more rubber has to deflect as it tracks across the surface. Increased
tire diameter decreases the degree of deflection. Rubber is not perfectly elastic, so some energy is lost.
 The force to roll a tire is therefore proportional to the normal force and the volume of rubber deflected per
second which is proportional to rotational velocity.
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Measuring Vehicle Efficiency
 EPA and real world fuel economy (Efficiency) is impacted by the vehicle’s drag force. Drag is determined by
taking a vehicle to 70 mph and then shifting into neutral and measuring speed versus time and thus deceleration
rate. Knowing the mass of the vehicle, a drag force versus vehicle speed can be derived. This drag force data is
fitted to a 2nd-order polynomial whose coefficients are published by the EPA – called the ABC coefficients.
 The chassis dyno where emissions and fuel economy data is taken has
 Rollers instead of pavement, with vehicle strapped down
 Only drive-wheels turning
 No aerodynamic loading
 The A,B,C coefficients determine the load which the dyno program must match over the course of the test cycle
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Vehicle Drag Force Example
A = 28.73 lb
B = 0.7338 lb/mph
C = 0.01084 lb/mph^2
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Evidence of Vehicle Efficiency
 EPA data shows that there is no magic. Following slides show every vehicle for sale in 2008 Model Year in the
US.
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Inertial Loads
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Aerodynamics
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Rolling Resistance
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Downsizing
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Typical Mid-Size Vehicle Energy Distribution
Idle
0.90
Aero
0.21
Accessories
0.17
Rolling
0.34
8.29 units
Engine
1.25
D/L
1.00
Kinetic
Engine Losses
5.97
Driveline Losses
0.25
Braking
0.45
Urban Federal Test Procedure (FTP)
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FTP City – Mid-Size Sedan Simulation
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Simulation – Level of Hybridization
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Simulation – Hybrids with Downsizing
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Simulation – Advanced Powertrain Tech
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Electric Vehicles & Fuel-Cell Vehicles
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Well-to-Wheels and Tank-to-Wheels
USA Energy Consumption (%)
1960
1970
1980
1990
2000
Oil
44.1
43.5
43.6
39.8
38.5
Natural Gas
27.5
32.1
26.0
22.9
23.7
Coal
21.8
18.1
19.6
22.8
22.7
Nuclear Energy
.002
0.35
3.5
7.3
8.1
Hydro-,Geothermal,Solar, Wind,etc
6.6
6.0
7.2
7.4
6.9
USA Electricity Generation (%)
1990
2000
Coal
52.6
51.8
Petroleum
4.1
2.9
Natural Gas
12.5
15.7
Nuclear
19.1
19.9
Hydroelectric
9.7
7.2
Geothermal
0.5
0.4
Wood
1.0
1.0
Waste
0.4
0.6
Other Waste
0.076
.09
Wind
0.099
0.129
Solar
0.020
0.021
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 Any true discussion of energy diversity and it’s impact on GHG must discuss
the source of energy (ie the Well)
 Electric Vehicles will receive the bulk of their energy from coal-fired generation
for foreseeable future
 Coal-fired electrical generation was 35% thermally efficient in 2005 (EPA)
 Line-losses and battery/e-motor efficiency aren’t 0%
 Therefore from a GHG perspective -TNSTAAFL
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Transportation Effects on GHG - Future
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By 2020,
1.1 billion vehicles (an increase of 300 million) will circle the earth 125 times.
Energy diversity is required in the future.
Reducing dependence on petroleum is imperative.
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“At GM, we believe tomorrow’s automobiles must be flexible
enough to accommodate many different energy sources.”
“ And a key part of that flexibility
will be enabled by the development
of electrically driven cars.”
- Rick Wagoner
Chairman and CEO
General Motors Corporation
LA Auto Show 11/29/2006
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Hybrid, Electric & Fuel Cell Vehicles
Vehicle Type
Electric
Power
Onboard
Electric
Storage
Grid
Connected
Recharging?
Electric
- only
Driving
Mild HEV
low
low
no
no
Full HEV
med
low
no
limited
PHEV
med
med
yes
limited
E-REV
high
high
yes
Full
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Electrification
Introduction & Background – More definitions
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Transportation Challenge –
Energy Diversity - Source Blending via Electrification
Oil
Petroleum Fuels
(Conventional)
Oil
Energy Carrier
Carrier
Energy
(NonConventional)
1st & 2nd Generation Biofuels
Biomass
Syngas
CO, H2
Coal
Natural Gas
(Solar, Wind, Hydro)
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Fischer
Tropsch
Plug-In
Hybrid
CCGT
Shift
Reaction
Thermochemical
Water-Splitting
Conventional ICE:
Gasoline/Diesel
Mild and Full
Hybrids
Electricity
Renewables
Nuclear
Liquid
Fuels
Propulsion System
Propulsion
System
Electrolysis
Extended Range
EV
Battery Electric Vehicle
Hydrogen
CO2
Sequestration
More Electrification
Conversion
Conversion
Battery Energy Storage
Energy Resource
Energy Resource
FC Electric Vehicle
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Transportation Challenge –
Energy Diversity - Source Blending via Electrification
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Advanced Technology and Sustainability…
GM Technology Strategy
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Chevrolet VOLT Concepts Illustrate
E-REV and FC Commonality
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Chevrolet VOLT E-REV Concept
•Global Compact Vehicle Based
•Electric Drive Motor
•120 kW peak power
•320 Nm peak torque
•Li Ion Battery Pack
•136 kW peak power
•16 kWh energy content
•Home plug in charging
•Generator
•53 kW peak power
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E-Flex Fuel Cell Variant
•Global Compact Vehicle Based
•Electric Drive Motor
•120 kW peak power
•320 Nm peak torque
•Fuel Cell Propulsion System
•Smaller Li Ion battery pack
•Hydrogen storage
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www.gm.com/corporate/careers/
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