2007-01-0292 

Platform Engineering Applied to Plug-In 

Hybrid Electric Vehicles 

Tony Markel 

National Renewable Energy Laboratory 

Copyright © 2007 SAE International

ABSTRACT 

Plug-in hybrid electric vehicle (PHEV) technology will 

provide substantial reduction in petroleum consumption 

as demonstrated in previous studies. Platform 

engineering steps including, reduced mass, improved 

engine efficiency, relaxed performance, improved 

aerodynamics and rolling resistance can impact both 

vehicle efficiency and design. Simulations have been 

completed to quantify the relative impacts of platform 

engineering on conventional, hybrid, and PHEV 

powertrain design, cost, and consumption. The 

application of platform engineering to PHEVs reduced 

energy storage system requirements by more than 12%, 

offering potential for more widespread use of PHEV 

technology in an energy battery supply-limited market. 

Results also suggest that platform engineering may be a 

more cost-effective way to reduce petroleum 

consumption than increasing the energy storage capacity 

of a PHEV. 

INTRODUCTION 

A plug-in hybrid electric vehicle (PHEV) is a hybrid 

electric vehicle (HEV) with the ability to recharge its 

energy storage system with electricity from an off-board 

power source. The key advantage PHEV technology has 

relative to hybrid electric and conventional vehicles is fuel 

flexibility. A PHEV uses the stored electrical energy to 

propel the vehicle and reduce petroleum consumption by 

the combustion engine. 

A recent study by Simpson estimates that a PHEV with 

usable electrical energy storage equivalent to 20 miles of 

electric travel (PHEV20) would reduce petroleum 

consumption by 45% relative to a comparable 

conventional combustion engine vehicle.[1] The purpose 

of the previous study was to quantify the impacts of 

PHEV technology alone. Elements of platform 

engineering were not considered. 

Platform engineering consists of enhancements that are 

not dependent on the powertrain technology and may 

include the use of lightweight materials, aerodynamic 

drag reduction, rolling resistance reduction, combustion 

engine efficiency improvement, and performance 

constraint relaxation. Each of these has the potential to 

improve overall vehicle efficiency. This paper will quantify 

the relative impacts of each platform engineering step on 

conventional, hybrid, and PHEV vehicle architectures. 

APPROACH 

This analysis employs a cost-benefit model detailed by 

Simpson.[1] It is a power-based model that iteratively 

solves for the component sizes (engine power, motor 

power, battery power, and energy) to meet performance 

constraints and energy consumption characteristics of 

the vehicle over standard driving profiles as a function of 

the equivalent electric range capability and the degree of 

hybridization. Consumption characteristics are calculated 

on the Urban Dynamometer Driving Schedule (UDDS) 

and the Highway Federal Test Procedure using a 

modified form of the SAE J1711 Recommended Practice 

as discussed by Gonder and Simpson.[2] The results are 

post-processed to determine the retail and operating 

costs of each vehicle scenario. The model runs quickly 

(a few seconds per vehicle scenario) and allows rapid 

exploration of the design space. 

In the previous study by Simpson, the impacts of PHEV 

technology where isolated by including no improvements 

to engine and platform attributes. This study expands on 

the previous work by including improvements to engine 

and platform attributes. Conventional, hybrid, and plug-in 

hybrid vehicles can all benefit from platform engineering. 

The retail cost models used in this analysis do not 

attempt to estimate the costs of implementing the 

platform engineering steps, but instead will reference the 

work of others as necessary. The models only account 

for changes in retail cost due to changes in the 

powertrain attributes. Retail cost is the manufacturer 

suggested retail price (MSRP) and is calculated from the 

sum of the component costs multiplied by manufacturer 

and dealer markups of 50% and 16.3% respectively. 

Midsize sedans are high volume vehicles in today’s 

marketplace. The baseline vehicle attributes for this 

analysis are representative of a typical midsize sedan, 

such as the Chevrolet Malibu or Toyota Camry. Table 1 

1

NREL/CP-540-41034. Posted with permission. 

Presented at the 2007 SAE World Congress 

April 16-19, 2007, Detroit, Michigan 
summarizes the attributes of the baseline conventional 

vehicle. 

Table 1: Midsize Sedan Platform and Performance 

Attributes 

Platform Parameters 

Glider mass 905 kg 

Curb mass 1429 kg 

Test mass 1565 kg (136 kg load) 

Gross vehicle mass (GVM) 1899 (470 kg load) 

Drag coefficient 0.3 

Frontal area 2.27m2

Rolling resistance coefficient 0.009 

Baseline accessory load 800 W elec. (4000 W peak) 

Performance Parameters 

Standing acceleration 0-97 kph (0-60 mph) in 8.0 s 

Passing acceleration 64-97 kph (40-60 mph) in 5.3 s 

Top speed 177 kph (110 mph) 

Gradeability 6.5% at 88 kph (55 mph) at GVM 

with 2/3 fuel converter power 

Vehicle Attributes 

Engine power 121 kW 

Fuel consumption 10.6 / 6.7 / 8.8 L per 100km 

(urban / highway / composite) 

MSRP $23,392 

The previous study identified PHEVs with all-electric 

range capability on the UDDS to be the most costeffective PHEV design scenarios.[1] Therefore, the 

scope of this study only considers PHEVs with all-electric 

range on the UDDS cycle. Both conventional 

combustion engine vehicles and charge-sustaining HEVs 

have been included for comparison. The impacts of five 

vehicle attributes influential in vehicle design and 

efficiency as detailed in Table 2 are evaluated in this 

study. 

Table 2: Platform Engineering Parameter Values 

Attribute Baseline Alternative 

Vehicle Glider Mass 905kg 815kg 

Peak Engine Efficiency 34% 37% 

0-60mph Acceleration Time 8s 10s 

Aerodynamic Drag Coef. 0.30 0.27 

Rolling Resistance Coef. 0.009 0.008 

Finally, the previous work by Simpson assumed that the 

usable window of the energy storage system in a PHEV 

would be specified to ensure 15-year life of all 

components based on statistical daily driving behaviors 

and limited battery cycle life data. The usable battery 

state of charge varied from 37% for PHEV20 to 73% for 

a PHEV60. Limiting the usable state of charge for shorter 

range PHEVs increases the total energy requirements 

and vehicle retail cost. High vehicle retail cost could be a 

challenging barrier to PHEV market penetration. The 

ability to fully utilize the onboard storage system capacity 

will be critical for reducing retail cost and maximizing 

operating efficiency. In this paper, the focus is on longterm scenarios, so it is assumed that all PHEVs will be 

able to utilize 70% battery depth of discharge. 

RESULTS 

The individual impacts of each of the five platform 

engineering improvements—mass reduction, engine 

efficiency improvement, acceleration constraint 

relaxation, aerodynamic drag reduction, and rolling 

resistance reduction—have been applied to a PHEV20 

vehicle. The results provide insight into the relative 

benefits of each for a specific powertrain. All of the 

attributes are then applied together to the conventional, 

HEV, and PHEV designs considered to quantify the 

combined potential benefits and identify how these 

benefits vary by powertrain design scenario. 

Figures 1 and 2 summarize the impacts of each platform 

engineering attribute and are discussed in the sections 

below. Energy costs were calculated assuming 15,000 

miles/year, $3/gal gasoline, and $0.09/kWh electricity. 

0

1

2

3

4

5

6

7

8

9

Curb Mass Battery Energy Battery Power Engine Power

Percent Decrease (%)

-10% Glider Mass

+10% ICE Eff.

8s to 10s 0-60 mph

-10% CD

-10% RRC

Figure 1: Platform Engineering Impacts on 

Powertrain Attributes of a PHEV20 

0

1

2

3

4

5

6

7

8

9

10

Gasoline

Consumption

Electricity

Consumption

Annual Energy

Cost

Retail Cost

Percent Decrease (%)

-10% Glider Mass

+10% ICE Eff.

8s to 10s 0-60 mph

-10% CD

-10% RRC

Figure 2: Platform Engineering Contributions to 

Costs and Consumption for a PHEV20 

MASS REDUCTION 

Reducing the mass of the vehicle is one of the most 

effective ways to increase vehicle efficiency. Today’s 

typical sedan weighs ~1600 kg and is often used to 

move a single ~75 kg person. The additional mass of the 

2
vehicle adds function, comfort, and convenience but 

leads to large amounts of wasted energy. 

Honda employed dramatic mass reduction technologies 

in developing the Insight HEV. Through the extensive 

use of aluminum, the body-in-white weighs ~40% less 

than a comparable conventional vehicle.[3] The Insight 

was the most fuel efficient vehicle commercially 

available. 

The mass of the vehicle glider in this study was reduced 

by 10% from 905kg to 815kg to assess the impact of 

mass reduction on a PHEV. A reduction of 90kg is 

significant but is achievable through the use of 

lightweight steels.[4] More extensive use of aluminum 

and composites can provide even greater weight savings 

(120 to 150kg) but are also more costly (~$500).[4] 

A reduction in glider mass of 10% allowed the engine 

power requirement to be reduced by 4.8%, and the 

battery energy requirement was reduced by 5.2% (Figure 

1). Both of these along with the actual glider mass 

reduction and compounding effects lead to a reduction in 

total curb mass of 8.1%. The mass reduction affects 

both electrical consumption and gasoline consumption 

nearly equally, and the net result is that the operating 

energy cost drops by 4.1% (Figure 2). The retail cost 

savings due to powertrain impacts alone of mass 

reduction was $1031 or 3.4%. Based on the literature, 

the savings is greater than the cost to implement a 10% 

reduction in glider mass. 

ENGINE EFFICIENCY 

Efficiency of the combustion engine in both conventional 

and hybrid vehicles is critical. Losses in the engine are 

the single greatest source of inefficiency in vehicles. 

Hybrid vehicle technology attempts to reduce these 

losses by allowing engines to operate under greater 

loads and eliminating low load and idle operation. 

In the baseline scenario, a peak engine efficiency of 34% 

is assumed. This is typical of today’s standard gasoline 

combustion engines. The peak efficiency occurs near 

50% of rated power and is significantly lower at lowerload fractions. The engines in the Prius, Camry, and 

Ford Escape HEVs all use an Atkinson combustion cycle 

to increase engine efficiency. To determine the relative 

benefits of engine efficiency improvements in a PHEV, 

the engine efficiency was increased by 10% from 34% 

for the baseline to 37% for the engineered scenario. 

PHEVs use very little if any gasoline in their initial 

charge-depleting operating mode but are fully dependent 

on gasoline in the charge-sustaining operating mode. 

Changing engine efficiency does not affect component 

sizing requirements. Therefore, improving engine 

efficiency simply reduces operating energy costs by 

reducing gasoline consumption. Gasoline consumption 

dropped by 9.3% and operating cost dropped by 8% 

Figure 2). Increasing engine efficiency had negligible 

impact on the powertrain attributes and thus provides 

little retail cost savings due to powertrain impacts. It is 

likely that engine efficiency improvements will be more 

effectively applied in short-range (equivalent energy of 20 

miles or less) PHEVs. If the average daily consumer 

travel distance is ~30 miles, the engine of a PHEV with 

20 miles of energy will be used in charge-sustaining 

mode (battery state of charge is maintained within a fairly 

small nominal window) more often as compared to 

PHEVs with 40 or more miles of energy. 

The cost of implementing engine efficiency 

improvements is uncertain. Lipman and Delucchi [5] 

suggest that VTEC (variable valve timing and lift 

electronic control) technology could be implemented at a 

cost of $360. Since engine efficiency improvements had 

little impact on retail cost the incremental costs may 

need to be offset by the reduced operating costs or by 

reduced retail cost impacts of other platform engineering 

steps. 

PERFORMANCE CONSTRAINT RELAXATION 

The baseline performance constraints for acceleration, 

top speed, and gradeability are detailed in Table 1. For 

hybrids these define the limits of downsizing the engine. 

For the midsize sedan, 8.0s 0-60mph acceleration 

capability is slightly better than the average of ~8.5s. 

Toyota has demonstrated with their first and second 

generation Prius models introduced in the United States 

that vehicles can be introduced and can achieve 

significant market penetration with less than class 

average acceleration. The MY2004 Prius was introduced 

with 0-60mph acceleration time of 10s. 

For a PHEV20, reducing the 0-60mph acceleration 

requirement from 8s to 10s reduces the engine size by 

2% (Figure 1). Engine size reduction leads to mass 

reduction and as a result the battery energy requirement 

is reduced. The combined impact is ~3.5% reduction in 

curb mass. Both petroleum and electricity consumption 

are reduced by 2% (Figure 2). Because both engine and 

battery sizes can be reduced, the retail costs are 

reduced by almost 2% or $550. There should be no 

offsetting technology costs to implement a reduced 

performance vehicle. 

AERODYNAMICS 

The impacts of aerodynamic drag are speed dependent 

and contribute substantially during highway operation. As 

the powertrain efficiency is improved through 

hybridization, aerodynamic losses begin to represent a 

greater share of total losses. A typical midsize sedan will 

have a drag coefficient of 0.3-0.35. The Honda Insight, 

Toyota Prius, and Honda Civic HEVs all have lower than 

class average drag coefficients of 0.25, 0.26, 0.28.[6] 

The overall body design substantially impacts the 

aerodynamic drag losses. However, other simpler 

elements, like the rear spoiler employed on the Civic and 

Saturn Vue hybrids and aerodynamic hubcaps as 

employed on the Civic and Insight, also can contribute. 

Honda went so far as to include body panels to enclose 

3
the rear wheels and an enclosed underbody for the 

Insight. 

For this study, the aerodynamic drag coefficient is 

reduced from 0.3 to 0.27. This is a moderate but 

significant reduction and within the realm of existing 

hybrid vehicles. The 10% improvement in aerodynamics 

leads to a 1.6% reduction in engine power requirement 

and 2.2% reduction in energy storage capacity 

requirement (Figure 1). Together, they provide a retail 

cost reduction of slightly less than 1% or $278 (Figure 2). 

No attempt has been made to quantify the additional 

costs of implementing a 10% reduction in aerodynamic 

drag. Lipman and Delucchi [5] suggest that this can be 

accomplished for under $176 for a midsize sedan. 

Aerodynamics biggest impact comes in reducing the 

energy consumption costs by 3.2%. 

ROLLING RESISTANCE 

The energy efficiency impacts of rolling resistance are 

mass dependent and thus affect vehicle efficiency both 

during urban and highway operation. Again, reduced 

rolling resistance tire technology has been employed on 

several of today’s HEVs, including the Insight, Prius, and 

Vue. A report published by Green Seal indicates that lowrolling-resistance replacement tires with acceptable 

performance and handling characteristics for the midsize 

car class have values of 0.0102 to 0.0081.[7] Therefore, 

the reduction from 0.009 to 0.008 rolling resistance 

coefficient as evaluated in this report is feasible and 

should have minimal additional cost for implementation. 

The Green Seal report also highlights that the cost of 

these quality low-rolling-resistance tires can vary greatly 

but in general cost nearly the same or just slightly more 

than traditional tires. 

Reduced rolling resistance provides improved operating 

efficiency across the full operating spectrum allows the 

battery energy requirement to be reduced by 3.5%. 

Some mass reduction is observed in addition to a 

reduction in engine size of 1.3% (Figure 1). Petroleum 

consumption is reduced by 3% and electricity 

consumption is reduced by 3.5% (Figure 2). As a result, 

operating energy costs are also reduced by 3%. The 

overall system cost is reduced by 1.2% or $362. 

Because the cost of implementing low-rolling-resistance 

tires is minimal, these powertrain cost savings could 

potentially be used to offset the cost of other more costly 

platform engineering steps. 

COMBINED EFFECTS OF PLATFORM ENGINEERING 

The impacts of each step of platform engineering has 

been summarized individually by their contributions to 

vehicle design and energy efficiency, which impact retail 

cost and operating cost respectively. The last step in this 

analysis is to apply all of the platform engineering steps 

together into a single vehicle and compare it to the base 

vehicle. 

Relative to the base vehicle, the curb mass of the 

PHEV20 with platform engineering is reduced by 12.5%. 

The substantial reduction in mass allows both the engine 

power and battery energy requirements to be reduced by 

9.7% and 12.6% respectively. Figure 3 shows that the 

actual glider mass reduction, the acceleration 

performance relaxation, and the mass compounding 

account for more than 75% of the total vehicle mass 

reduction. 

8s to 10s 0-60 

mph

26%

-10% Glider 

Mass

47%

Mass 

Compound

16%

+10% ICE Eff.

3%

-10% CD

4%

-10% RRC

4%

Figure 3: Contributions to Total Mass Reduction 

Achieving substantial mass reduction in combination with 

reducing aerodynamic and rolling resistance losses 

dramatically reduces the energy capacity requirements 

for a PHEV. In Figure 4, a PHEV20, 30, and 40 can all 

reduce their energy capacity by more than 12.5% while 

the PHEV10 achieves slightly less than 12% reduction. 

Assuming that the energy battery manufacturing industry 

for hybrid vehicles will be supply limited, platform 

engineering becomes extremely important for achieving 

the greatest reduction in petroleum consumption with a 

limited supply of energy batteries. 

11

11.5

12

12.5

13

PHEV10 PHEV20 PHEV30 PHEV40

Reduction Energy Capacity (%)

Figure 4: Platform Engineering Reduces PHEV 

Energy Capacity Requirements 

Platform engineering affects the design and efficiency of 

all vehicle architectures not just PHEVs. Two scenarios 

for four vehicle architectures are depicted in Figure 5. All 

four vehicles—conventional, hybrid, PHEV20 and 

PHEV40—were modeled with the baseline assumptions 

4
and with platform engineering implemented. The plot 

shows the estimated retail cost of each scenario with 

respect to the annual petroleum consumption of each. 

The consumption is calculated assuming 15,000 miles of 

travel per year. 

20

22

24

26

28

30

32

34

36

200 300 400 500 600 700

Petroleum Consumption (gal/yr)

Retail Cost (1000's US$)

Conventional

Hybrid

PHEV20

PHEV40

Baseline

Platform

Engineering

Figure 5: Cost and Consumption Impacts of Platform 

Engineering 

For the platform engineered vehicles, gradiated arrows 

are drawn to indicate the unquantified additional costs to 

implement the technology improvements in the vehicle. 

For each case, moving from the diamond to the 

corresponding square, there is a retail cost savings due 

to changes in powertrain ranging from slightly less than 

$1000 for the PHEV20 to close to $2000 for the HEV. 

Ideally, the powertrain cost savings would more than 

offset the platform engineering costs. Based on the 

literature cited, the cost to implement the platform 

engineering steps discussed is likely to be ~$1000 with a 

large window of uncertainty. 

The PHEV20 and PHEV40 in the baseline case reduce 

petroleum consumption by 46% and 58% respectively. 

Application of platform engineering continues to reduce 

the petroleum consumption of these vehicles. The 

PHEV20 with platform engineering achieves nearly the 

same petroleum consumption reduction as the PHEV40 

baseline vehicle. The conventional vehicle with platform 

engineering achieves petroleum reduction slightly greater 

than the hybrid baseline. Likewise, the hybrid with 

platform engineering achieves nearly the same 

consumption reduction as the baseline PHEV20. 

From the chart it seems that PHEVs don’t have as much 

to gain with regard to petroleum consumption from 

platform engineering steps. However, platform 

engineering helps PHEVs not only reduce petroleum 

consumption by 20%, but also reduces their electrical 

consumption by more than 12.5%. Platform engineering 

is a cost effective way of making vehicles much more 

efficient regardless of the source of the energy. 

CONCLUSION 

Previous analysis used vehicle systems simulation to 

determine the vehicle design attributes and consumption 

characteristics for a full spectrum of PHEV scenarios. 

This study extends the results of the previous work by 

applying platform engineering and quantifying its impacts 

on PHEV design and benefits. The impacts of mass 

reduction, improved engine efficiency, relaxed 

performance constraints, aerodynamic drag, and rolling 

resistance improvements were evaluated when applied 

to conventional, hybrid, and PHEVs. 

Various degrees of platform engineering are already 

employed in energy-efficient vehicles. The magnitude of 

the improvements considered in this study is similar to 

those included in available vehicles. 

Mass reduction and relaxed performance constraints 

allow the combustion engine to be downsized. Engine 

downsizing coupled with improved engine efficiency, 

aerodynamics, and rolling resistance greatly enhance 

overall vehicle efficiency. For PHEVs, the improved 

vehicle efficiency due to platform engineering reduces 

energy storage system capacity by more than 12%. 

Platform engineering allows a limited supply of batteries 

to be used in more PHEVs and thus have a greater 

impact on total petroleum consumption. 

ACKNOWLEDGMENTS 

The author would like to acknowledge the outstanding 

contributions of Andrew Simpson for the development of 

the cost-benefit systems analysis tool used to complete 

this study. Additionally, the author would like to 

acknowledge the programmatic support of the U.S. 

Department of Energy Office of Energy Efficiency and 

Renewable Energy FreedomCAR and Vehicle 

Technologies Program. 

REFERENCES 

1. Simpson, A. “Cost-Benefit Analysis of PHEV 

Technology.” 22nd International Electric Vehicle 

Symposium. Yokohama, Japan. October 2006. 

2. Gonder, J. and Simpson, A. “Measuring and 

Reporting Fuel Economy of Plug-In Hybrid Electric 

Vehicles.” 22nd International Electric Vehicle 

Symposium. Yokohama, Japan. October 2006. 

3. “Interactive Encyclopedia: Aluminum Construction.” 

http://www.insightcentral.net/encyclopedia/enaluminu

m.html. Accessed October 27, 2006. 

4. Frangi, A. “Lightweighting and Alternative Vehicle 

Propulsion Systems.” Presented at MIT Material 

Systems Lab Steering Committee Meeting. April 20, 

2001. 

5. Lipman, T. and Delucchi, M. “Hybrid-Electric Vehicle 

Design Retail and Lifecycle Cost Analysis.” UCDITS-RR-03-01. April 2003. 

6. “Aerodynamic Design.” 

www.hybridcars.com/aerodynamic-design.html. 

Accessed October 27, 2006. 

7. “Choose Green Report.” Green Seal. March 2003. 

http://www.greenseal.org/resources/reports/CGR_tir

e_rollingresistance.pdf. Accessed October 27, 2006. 

5
CONTACT 

Tony Markel, Senior Research Engineer, National 

Renewable Energy Laboratory (NREL), 1617 Cole Blvd; 

Golden, CO 80401 USA; Phone: 303.275.4478; Fax: 

303.275.4415; e-mail: tony_markel@nrel.gov. 1996-

Present NREL; 2002-2005 MS Mechanical Engineering 

from University of Colorado; 1995-1996 Argonne 

National Laboratory; 1991-1995 BSE Mechanical 

Engineering from Oakland University. 

DEFINITIONS, ACRONYMS, ABBREVIATIONS 

PHEVx: A plug-in hybrid electric vehicle with a usable 

energy capacity equivalent to x miles of electric operation 

on a standard urban driving profile. It may or may not 

travel x miles all-electrically depending on the operating 

strategy 

6