Medium- and Heavy-Duty 

Powertrain

Hardware-in-the-Loop

Test System

Dec. 10, 2014

1
Outline

• Overview of Powertrain Hardware-in-the-Loop (HIL) 

test systems

• Test cell specifications

• Repeatability and COV

• Recognizing sources of COV

• Improvements to test system

• Test system measurements for drive-cycle MPG

• Notes on comparisons to other test systems

2
Vehicle GHG Evaluation:

Capturing the big picture?

3

Engine

HIL

Powertrain

HIL

Vehicle

HDC

On-Road

Vehicle

Full

Simulation

Simulation

and tuning

effort

Relative

Cost

Hardware

Extent

Relative

Uncertainty

Simulation

Extent
Vehicle GHG Evaluation:

Capturing the big picture?

• Full simulation

– Cost and technical uncertainty high

• Engine dyno tests

– Historical repeatability and cost understood 

• Powertrain test cell

– Repeatability and cost understood 

• Vehicle HDC

– Repeatability and cost understood 

• On-Road vehicle

– Cost to provide acceptable repeatability/uncertainty high

4
Another View of Various Methods to Measure 

GHG Emissions 

5

Greenhouse 

Gas Emission 

Model [GEM] 

HD 

Chassis 

Powertrain 

Test Cells 
Background on Powertrain Testing

• Capture key interactions between engine and transmission

• Evaluate powertrain as if in vehicle

• Allows for expansion to hybrid or other energy management 

technology

6

Conventional HD Testing: Powertrain in the Loop:Motor/Gen

Battery

Internal

Combustion

Engine

Internal

Combustion

Engine Transmission
Test Cell Specifications

• Test Cell specifications similar to conventional 

engine dynamometer test cell

• Dynamometer sizing different than 

conventional engine test cells 

7
Test Cell Specifications:

Dynamometer requirements

8

0

5000

10000

15000

20000

25000

0 500 1000 1500 2000 2500 3000 3500

Transmission Output Shaft Torque [Nm]

Transmission Output Shaft Speed [RPM]

1

2

3

4

5

6

7

8

9

1 0

Nominal Dyno Capacity

175% Dyno Capacity

Max Torque w/Brake

Gear #

Simplified theoretical analysis 

says that torque requirements in 

low gears may be excessive, 

requiring very large 

dynamometer 

1

2

3

5

4

6 7 8

9

10

Heavy-duty

example shown
Test Cell Specifications:

Powertrain Torque Over Drive Cycle vs. Dyno Capacity

24-Jun-2014 9

0

5000

10000

15000

20000

25000

0 500 1000 1500 2000 2500 3000 3500

Transmission Output Shaft Torque [Nm]

Transmission Output Shaft Speed [RPM]

WHVC

Nominal Dyno Capacity

175% Dyno Capacity

Maximum Torque w/Brake

Each drive cycle has different 

torque capacity requirements.

Periods of highest torque 

demand are often very brief.

Heavy-duty

example shown
Medium-Duty Powertrain

10
Example from Current Program:

Medium-Duty Powertrain Vehicle

24-Jun-2014 11

F650 Flat Bed Tow Truck 

• Cummins ISB 6.7L I6

• 2010 compliant

– EGR, DOC,DPF,SCR

• Allison 2200 RDS

– 5-speed Automatic

• Coastdown data 

created under 

separate task

• Heavy Duty Chassis 

Dyno(HDC) testing 

under separate task
Powertrain HIL

Test System Configuration

12

Pedal Position

(Torque Command)

Dyno 

Motor

Speed 

Control

Driveshaft 

Torque/Speed 

Feedback

Driveshaft

Speed

Command

dSPACE MABX I 

(Vehicle simulation)

Pedal,

Driveshaft

Speed

Target

Cycle Speed
MD Powertrain HIL Test Cell at SwRI

13

445 kW DC

motor/dyno

Friction brake for

zero speed control 

inline torque meter 

Eddy current dyno for 

high absorption tests

Powertrain
MD Powertrain Test Cell Setup

• SwRI Heavy Duty Transient Data 

Acquisition (HDT)

– pressures/temperatures, CAN, LAN, serial, etc.

• DSpace Real-Time Simulation

– enhanced GEM model for vehicle simulation

• Horiba Raw Emission Bench

– CO2, CO, THC, and NOx

• LFE airflow

• Coriolis fuel flow meter

• BG3 PFD for particulate matter 

measurement

14

Test cell utilizes many 

sub-systems that are 

already available for 

most conventional 

engine-dyno test cells.

Test cell has been 

repeatedly reconfigured 

as Powertrain or Engine 

test cell during this 

program. 
Transient Cycles

considered for this study

15

CARB WHVC

CILCC PARCEL
Transient Cycles –

Decomposed as Time at Various Speeds

16

Differences in cycle speed demand provides 

breadth for study of Powertrain HIL test system 
System Validation:

Vehicle Speed vs Cycle-Defined Speed

17

0

5

10

15

20

25

0 1000 2000 3000 4000 5000 6000 7000

Vehicle Speed [m/s]

Cycle Time [msec]

F650 ARB Vehicle Speed Desired

Vehicle Speed Actual

Vehicle Max Speed

Vehicle Min Speed

0

5

10

15

20

25

2550 2650 2750 2850 2950 3050 3150 3250 3350 3450

Vehicle Speed [m/s]

Cycle Time [msec]

F650 ARB

Note that a “good” test is 

not necessarily a 

repeatable test. The Driver 

is critical to repeatability. 

Note that the driver 

could have driven a 

“good” test many 

different ways 
System Validation:

Powertrain Torque vs Theoretical Requirement

18

-500

0

500

1000

1500

2000

0 100 200 300 400 500 600 700

Trans Output Torque [N-m]

Cycle Time [sec]

Theorectical_torque N-m F650 ARB

Torque N-m

-500

0

500

1000

1500

2000

Trans Output Torque [N

255 265 275 285 295 305 315 325 335 345

-m]

Cycle Time [sec]

F650 ARB – Detail of 100 Seconds

Meeting vehicle load 

requirements depends 

upon minimizing vehicle 

speed deviations and dyno

load-control deviations. 
Repeatability:

Pedal Position for 5 tests

19

0

10

20

30

40

50

60

70

80

90

100

0 1000 2000 3000 4000 5000 6000 7000

Driver Pedal Position

Run 1

Run 2

Run 3

Run 4

Run 5

(ARB cycle)

Here we show that the 

driver model is (nearly) 

repeating the same 

movements for several 

drive-cycle repeated tests 0

20

40

60

80

100

2650 2670 2690 2710 2730 2750

The software driver is repeatable
Repeatability:

Vehicle speed for 5 tests

20

-5

0

5

10

15

20

25

0 1000 2000 3000 4000 5000 6000 7000

Vehicle Speed [m/s]

Run 1

Run 2

Run 3

Run 4

Run 5

(ARB cycle)

So, the software driver is driving 

the same every cycle, closing 

the loop on the required 

vehicle speed

...If the driver is 

repeatable, the vehicle 

speed will be repeatable
Repeatability:

Torque for 5 tests

21

-500

-300

-100

100

300

500

700

900

1100

1300

1500

1700

1900

0 1000 2000 3000 4000 5000 6000 7000

Torque [N-m]

Run 1

Run 2

Run 3

Run 4

Run 5

(ARB cycle)

The dyno-controller is also 

very repeatable, leading to 

excellent repeatability for 

vehicle speed and load.

Repeatability is also successful for 

vehicle load

-500

-300

-100

100

300

500

700

900

1100

1300

1500

1700

1900

2650 2700 2750 2800

Run 1

Run 2

Run 3

Run 4

Run 5
Repeatability:

Exhaust Temperature for 5 tests

22

0

50

100

150

200

250

300

350

400

0 1000 2000 3000 4000 5000 6000 7000

Exhaust Temp

Run 1

Run 2

Run 3

Run 4

Run 5

(ARB cycle)

Exhaust temperatures follow the success 

of the speed and load controllers
Repeatability:

Engine Coolant Temperature for 5 tests

23

70

75

80

85

90

95

100

0 1000 2000 3000 4000 5000 6000 7000

Engine Coolant Temp

Run 1

Run 2

Run 3

Run 4

Run 5

(ARB cycle)

Engine coolant temperature exhibited 

some variation, cycle-to-cycle.

...these differences warranted 

closer study
Repeatability:

FE Coefficient of Variance (COV) for larger numbers of tests 

24

55 mph 65 mph CARB WHVC Utility Parcel

Add 10% Cd -3.7% -5.1% -0.9% -1.5% -0.3% 0.4%

Add 10% Crr -2.7% -1.3% -1.4% -1.4% -1.4% -1.0%

Add 363 Kg -0.5% -0.3% -2.8% -1.9% -2.1% -1.6%

Baseline - - - - - -

EPA Optimized 5.9% 6.7% 2.2% 4.4% 2.6% 2.1%

Minus 10% Cd 4.7% 5.0% 0.5% 2.0% 0.4% 0.8%

Minus 10% Crr 1.4% 1.0% 1.6% 2.5% 2.3% 1.5%

COV

55 mph 65 mph CARB WHVC Utility Parcel

Add 10% Cd 0.66 0.11 0.09 0.09 0.30 0.27

Add 10% Crr 0.78 0.12 0.23 0.23 0.57 0.12

Add 363 Kg 0.90 0.60 0.29 0.29 0.58 0.15

Baseline 0.21 0.21 0.39 0.39 0.30 0.77

EPA Optimized 0.61 0.87 0.44 0.44 0.37 0.23

Minus 10% Cd 0.34 0.33 0.19 0.19 0.85 0.46

Minus 10% Crr 1.50 0.59 0.10 0.10 0.23 0.54

• Fuel Economy COV very good for CARB and WHVC cycles

• As program expanded number and type of test cycles, it became 

clear that other sources of uncertainty were being experienced

Vehicle Config / Cycle

Fuel Economy COV
Repeatability:

Finding sources of uncertainty/poor repeatability

25

7.34

7.53

7

7.1

7.2

7.3

7.4

7.5

7.6

7.7

35 55 75 95

Fuel Economy, MPG

Transmission Temperature, degC

CAC Temperature 46C

Parcel Cycle

7.34

7.28

7

7.1

7.2

7.3

7.4

7.5

7.6

7.7

20 30 40 50

Charge Air Cooler Temperature, degC

TransmissionTemperature 42C

Several studies performed Parcel Cycle

to locate and mitigate 

effects of system variables
Key Findings

• Similar to conventional engine dyno cells, 

Powertrain HIL test cell repeatability can be 

improved by control of system variables such as:

– Coolant temperature setpoints (heat exchanger control)

– Transmission temperature setpoints (heat exchanger control)

– Charge air temperature setpoints (heat exchanger control)

• Selection of controllable/repeatable setpoints may 

create drive-cycle fuel economy differences 

compared to other test systems

– Powertrain HIL Test System may be slightly different than Chassis Dyno

or Truck-on-Road

– Again, these distinctions have been recognized previously for engine 

test cell vs Truck-on-Road 

26
Attention to Detail

• Like Engine-based or Chassis-dyno-based, Powertrain HIL 

must be “prepped” carefully

– Forced DPF regeneration at regular intervals between 

tests

– Several “prep” cycles run before “official” cycle

 Stabilize initial conditions and powertrain system recent history

• Post-test

– Review large data sets to identify repeatability issues

 Driver

 Transmission gear selection

 Aftertreatment thermal management

 Other uncontrolled variables...

27
Repeatability:

FE COV and average fuel economy effects for various factors

Fuel Economy Effects

55 mph 65 mph CARB WHVC Utility Parcel

Add 10% Cd -3.7% -5.1% -0.9% -1.5% -0.3% 0.4%

Add 10% Crr -2.7% -1.3% -1.4% -1.4% -1.4% -1.0%

Add 363 Kg -0.5% -0.3% -2.8% -1.9% -2.1% -1.6%

Baseline - - - - - -

EPA Optimized 5.9% 6.7% 2.2% 4.4% 2.6% 2.1%

Minus 10% Cd 4.7% 5.0% 0.5% 2.0% 0.4% 0.8%

Minus 10% Crr 1.4% 1.0% 1.6% 2.5% 2.3% 1.5%

Fuel Economy COV

55 mph 65 mph CARB WHVC Utility Parcel

Add 10% Cd 0.66 0.11 0.09 0.09 0.30 0.27

Add 10% Crr 0.78 0.12 0.23 0.23 0.57 0.12

Add 363 Kg 0.90 0.60 0.29 0.29 0.58 0.15

Baseline 0.21 0.21 0.39 0.39 0.30 0.77

EPA Optimized 0.61 0.87 0.44 0.44 0.37 0.23

Minus 10% Cd 0.34 0.33 0.19 0.19 0.85 0.46

Minus 10% Crr 1.50 0.59 0.10 0.10 0.23 0.54

28

This data was 

taken during the 

midpoint of the 

overall program.

Improvements to 

the test system 

accuracy and 

repeatability 

continued to occur 

throughout 

program
Another View of Fuel Economy Parametric 

Study in a Powertrain HIL Test Cell

29

+10%Cd

10.05

+10%Crr

9.998

+363kg

9.862

Baseline

10.14

Optim

10.37

-10%Cd

10.19

-10%Crr

 10.3 9.8 9.9 10.0 10.1 10.2 10.3 10.4

CARB

Fuel.Economy

+10%Cd

10.05

+10%Crr

9.998

+363kg

9.862

Baseline

10.14

Optim

10.37

-10%Cd

10.19

-10%Crr

 10.3 9.8 9.9 10.0 10.1 10.2 10.3 10.4

CARB

Fuel.Economy

Conducted test matrix varying vehicle aero and drag 

coefficients and weight to study FE sensitivity

CARB Cycle

Test Configuration

Scale of 1% Fuel 

Economy differences 
Ongoing Activity:

Heavy-Duty Powertrain HIL System Setup

• International ProStar

– Navistar N13 13L I6

– 2010 compliant (EGR, 

DOC,DPF,SCR)

– Eaton UltraShift Plus LSE 

16Speed AMT

– Class 8 Linehaul

– Coastdown performed

– On road constant speed tested

24-Jun-2014 30
Ongoing Activity:

Heavy-Duty Powertrain HIL System Setup

31

• Engine-only 

shakedown tests 

complete at 2 

power ratings

• Powertrain

system installed 

and ECU, TCM 

communication 

established

• First test runs 

completed 

November, 2014

Test cell available 

for tour
Key notes for

Powertrain HIL Test Cell

• All driving accomplished by driver model

– Driver variability is minimized

– Driver tuning is available – not all cycles the same

• Vehicle variability downstream of transmission is 

eliminated

– Driveshaft

– Differential and axles

– Tires and Rolls

• Closed-Loop temperature control available for most 

subsystems

– CAC, engine coolant, transmission temp, fuel temp, etc

• Dual-use test cell - Traditional engine or powertrain test 

system

32
Summary

• SwRI set up and demonstrated 2 Powertrain

HIL test cells under contract from EPA

– Medium- and Heavy-duty

– Both cells utilize conventional engine test cell 

equipment, reconfigured for Powertrain HIL studies

• Preliminary results from MD Powertrain HIL 

indicate

– Repeatability similar to that available from 

conventional engine test cells (COV ~0.2-0.5) 

 Inclusion of vehicle modeling capability, transmission, and 

added networking at test cell did not degrade data quality 

33
Summary

• HD Powertrain HIL test system is operational 

and evaluation of performance and 

repeatability now initiated

• Separate tasks in overall EPA program are 

comparing different engine/powertrain/truck 

GHG measurement systems

– Engine HIL

– Powertrain HIL

– Heavy-duty Chassis dynamometer

34