May 21 , 2012

EPA Technical Memorandum

Subject : Energy Recovery Testing for GM Silverado 2

- Mode Hybrid and other Hybrid Light

duty Vehicles

From : James Sanchez, Ben Ellies , U.S. Environmental Protection Agency



## -----------------------------------------------------------------------------

Introduction

To provide additional data to inform the technology incentive credit program for full

- size pickup
truck s proposed for the EPA and NHTSA 2017

- 2025 light duty vehicle greenhouse gas and
CAFE programs , EPA tested a full

- size pickup truck hybrid along with several other hybrid vehicles at the National Vehicle and Fuels Emission Laboratory (NVFEL). The results can be used to help inform the performance criteria fo r defining mild and strong full size pickup truck hybrids

. 1 The performance metric evaluated by the test program is based on the amount of energy that is absorbed by the battery compared to the kinetic energy that is available from the
vehicle over a Cold and Hot Urban Dynamometer Driving Schedule (UDDS) . The testing and analysis of the data for a GM Silverado Hybrid are described in detail in this memo along with the summary results from the other hybrid vehicles tested at NVF EL over the past year 2

.

1 See 76 FR 74879 (Section I.B.4.e of the joint preamble) and Chapter 5.3 of the draft Joint Technical Support Document for the Joint Notice of Proposed Rulemaking for a detailed discussion of the proposal regarding the full

- size pickup truck technology incentive cred it, and the proposed test procedure and performance metric for distinguishing between mild and strong hybrid vehicles.

2 These additional hybrid vehicles (passenger cars, cross

- overs, and sport

- utility vehicles, ) were tested for purposes other than measur ements to inform the full

- size pickup truck technology incentive credit, however, data was collected during those tests regarding current flow into the hybrid battery system which is informative and therefore presented here.Vehicle Description

Table 1

– Description of vehicle tested.

Make GM

Model Silverado 2

- Mode Hybrid

Year 2012

Beginning Odometer (miles) 4435

Test Weight (lbs) 6000

Target 2WD Dyno Set 4WD Dyno Set

A Coefficient (lbf) 51.63 30.93 7.39

B Coefficient (lbf/mph) 0.105

- 0.1621

- 0.2143

C Coefficient (lbf/mph^2) 0.034 0.03434 0.033

Fuel Certification Gasoline

Since this t ruck is the only full size pick

- up truck strong hybrid commercially available, EPA requested a loan of this vehicle from General Motors for the purposes of characterizing a strong hybrid. In April 2012, General Motors provided this truck to EPA for testing.Test Plan

To prepare the vehicle the fuel tank was drained and filled to 60% of capacity. The dynamometer set coefficients were then derived with the dynamometer configuration in 2 and 4
wheel drive mode. The vehicle was the n driven over the UDDS cycle the day before the first set
of tests were run.

A current clamp was connected around the positive high voltage DC cable going from the power
electronics to the nickel

- metal hydride hybrid battery. The specific location was under the air
filter box which is on the left side of the engine compartment. A Hioki 3193 meter was used to integrate a nd save the current data. The actual battery voltage was unable to be measured since
there was no access to the electrical leads. The nominal battery voltage was used for all
calculations.

The vehicle was then tested over a cold UDDS, 10 minute soak and then a hot UDDS . The
vehicle was tested once each day until there were 3 repeats with the dynamometer configured in 2 and 4 wheel drive mode. Along with the high voltage DC battery current, dilute CO2, CO, NOx, THC, and CH4 were measured.

Data Ana lysis

Available Brake Energy

The theoretical maximum available brake energy over the schedule , E brake_max , was calculated using the vehicle’s equivalent test weight (ETW) and target coastdown coefficients A, B and C. The integration of the brake energy was done with a 10hz version of the UDDS schedule.

Where:

i = a counter to indicate a point in time over the driving schedule in seconds

.

A = constant value representing the vehicle’s frictional load in N

.B = coefficient representing load from drag and rolling resistance, which are a function of

vehicle speed in N∙s/m.

C = coefficient representing aerodynamic effects, which are a function of v ehicle speed squared
in N∙s 2 /m 2

.

V = linear speed of the vehicle (in the case of the Silverado) or schedule (for the other vehicles tested) , in mph or m/s.

M = mass of vehicle in kg.

t = elapsed time in the driving schedule.

P = road load power in kW.

E = brake energy in kW

- hr

Per the above equations, the final valu e of E i (at the last time point in the trace) represents

E brake_max

.

Note that the A, B and C coefficients are typically reported in English units (lb, lb/mph and lb/mph 2 ), and as such must first be converted to their metric equivalents. The expression (A+Bv+Cv 2 ), combined with vehicle speed in mph, can be converted to N by multiplying by
4.448.

Electrical Energy to Battery

The electrical energy to the battery was measure d with the Hoiki 3193 meter with the current clamp between the battery and the power electronics. Th is location it consistent with where the current clamp is installed for the SAE J1711 state

- of

- charge ( SOC ) check. The amp

- hours ( A

hr ) to the battery was integrated with the Hioki meter

. The notation used was : current going to
the battery is negative and current out of the battery is positive.The current data was also integrated only during the braking portions of the cycle.

I = current in and out of battery in ampere.

Ahr = electrical charge transfer in and out of battery in ampere

- hour.

E recovered is calculated by multiplying the nominal voltage (as reported by the manufacturer) to
the final value of Ahr i (at the end of the test).

R esults for 2

- mode Silverado Pickup Truck

The emissions results and battery SOC change are summarized in Table 2. Since there wasn’t a significant offset between tests with the dynamometer in 2 and 4 wheel drive mode the mean, standard deviation, coefficient of variance ( COV ) were calculated using all of the tests. The test to test variability of CO2 emission rate is correlated with battery SOC change over the test. The

t ests with a larger amount of energy flowing out of the battery had lower CO2 emission s tha n the tests with less energy com ing from the battery.Table 2

– Summary of gaseous emissions and battery SOC change for 2

- mode Silverado Pickup Truck Hybrid

.

Test # Dyno Mode CO2 HC

- FID CO NOx CH4 NMHC Delta SOC

g/ mi le A

- hr

(+ is energy out of battery)

1 2 wheel drive 502.7 0.0730 1.152 0.0198 0.0160 0.0566 0.06 0

2 2 wheel drive 440.0 0.0445 1.261 0.0222 0.0165 0.0277 0.238

3 2 wheel drive 444.2 0.0484 1.390 0.0227 0.0184 0.0299 0.189

1 4 wheel drive 459.2 0.0499 1.565 0.0227 0.0199 0.0299 0.146

2 4 wheel drive 471.8 0.0841 1.822 0.0247 0.0231 0.0605 0.068

3 4 wheel drive 474.3 0.0883 1.807 0.0234 0.0238 0.0641 0.124

Mean 465.36 0.065 1.500 0.023 0.020 0.045 0.138

Standard
Deviation 23.00 0.019 0.280 0.002 0.003 0.017 0.069

COV 5% 30% 19% 7% 17% 39% 50%Energy Results for 2

- mode Silverado Pickup Truck and Additional Vehicles

Table 3 is a summar y of the available brake energy (E brake_max ) , total energy to battery (E recovered ) and energy to the battery during braking for the Silverado and additional hybrid vehicles tested at
the NVFEL

. Except for the Silverado, Hioki data (originally recorded at 1 Hz) for all vehicles
was post

- processed from earlier hybrid vehicle emissions tes ts , as documented in the attached Excel spreadsheet . The exact measurement location for each test vehicle was not known, although it was in accordance with the standard state

- of

- charge balance confirmation protocol
used for all hybrid vehicle certification testing.

Table 3

– Summary of available brake energy and energy to the battery.

Theoretical Total Charging Decel

- only Charging

E brake_max E recovered % of Test data % of

type kWh kWh E brake_max kWh E brake_max

Lacrosse Mild

- 1.666 0.34 20% 0.15 9%

Civic H IMA

- 1.234 0.63 51% 0.32 26%

Prius V Strong

- 1.430 1.19 84% 0.54 38%

Camry Strong

- 1.519 1.58 104% 0.81 53%

Highlander Strong

- 2.048 1.90 93% 0.94 46%

CT 200h Strong

- 1.325 1.16 87% 0.56 43%

Silverado 2

- mode Strong

- 2.287 1.67 73% 0.97 42% 6

- test avg

Attachment: Braking energy calculator (4

- bag ) 052112 .xlsx