Heavy Duty Chassis Dyno Background 

Southwest Research Institute

10th December 2014

1
Outline

• Specifications

– Dyno rolls & torque capacity, cooling fan, HVAC, CVS & PM 

system

• Overview

– Free-body, coastdown, test cycles

• Instrumentation & Features

– DAQ, fuel measurement, drive by wire, variability control

• Vehicles Tested

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SwRI Heavy Duty Chassis 

Dyno

Specifications

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HD Chassis Dynamometer Specifications

4

• Two 48 inch diameter rolls

• 300 hp DC motor on each 

roll

• 250 hp road speed fan

• 100 ton HVAC system

• CVS System

• Horiba 7200D emissions 

bench

• SwRI developed fuel cart

• 1066 compliant

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HDC Specifications: Dyno Rolls & Torque Capacity

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• Twin 300 hp DC rolls

– Class 8 vehicles

– All wheel drive vehicles

– 7500 lb vehicle weight minimum

• 4500 lb each

– Typical light duty vehicle weight

– Average mass simulation of ~68,000 

lb
HDC Specifications: Cooling Fan

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• 250 hp fan

• Fully retractable

• Capable of simulating road 

speeds of over 100 mph
HDC Specifications: HVAC System

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• Two 50 ton units

• Installed November 

2012

• 40CFR 1066 

compliance 
HDC Specifications: CVS & Emissions Measurement

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• MEXA 7200D emissions measurement system

• CO2, CO, NOx, THC

• CH4 measurement with bag sampling system

• CVS sampling system

• Up to 3,000 CFM

• 47 mm PM measurement system
Heavy Duty Chassis Dyno 

Overview

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Overview: Setup

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Engine Trans

Driveline 

Wheels

Torque

Speed

Physical Inertia, 

Friction 

Dyno-Set simulated 

inertia, road load

T

1

Cut

• Typical engine testing is just that, the engine

• Powertrain testing includes the transmission

• Heavy Duty Chassis Dyno

– Includes powertrain and driveshaft, differential, wheels, inertia, 

and friction
Overview: Coast-downs

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• Inputs to controller

– Mass

– Cd, Crr from on-road 

coastdowns

• Perform coast-down on chassis 

dynamometer

– Iterative process to account for 

friction

0

1000

2000

3000

4000

5000

6000

0 5 10 15 20 25 30 35

Force (N)

Speed (m/s)

Typical Coast-Down Procedure

Target

1st Iteration

Acceptable
Overview: Typical Test Cycles

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• ARB Transient 

– Short transient

• World Harmonized Vehicle Cycle

– Medium length, mixture transient and 

steady state 

0

5

10

15

20

25

0 100 200 300 400 500 600 700 800

Speed (m/s)

Time (s)

ARB Transient Cycle

• Parcel Cycle

– Long low speed transient, heavy idle 

time

• Utility Cycle

– Long, low speed transient
Heavy Duty Chassis Dyno 

Instrumentation

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Instrumentation: Data Acquisition

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• SwRI internally developed system “HDT”

– Utilizes NI hardware 

– Numerous voltage, frequency, CAN inputs and 

outputs

– Ethernet communication with Horiba emissions 

bench

 Allows for calibration of instruments remotely

• Continuous measurement of emissions per 

40CFR part 1065

• Emissions results when test ends

– Outputs grams of each constituent
Instrumentation: Fuel Cart

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• SwRI developed fuel flow system

– Coriolis style mass flow meter

– Closed loop temperature & pressure controlled

– Captures transient operation

 Improved carbon balance error

 Detect small changes for development

0

10

20

30

40

50

60

70

0

10

20

30

40

50

60

3800 4000 4200 4400 4600 4800 5000

Fuel Flow [kg/hr]

Time [msec]

Day Tank

Cart

CAN Fueling
Heavy Duty Chassis Dyno 

Variability Sources & Mitigation 

Approaches

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HDC Variability

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• Heavy duty chassis dynamometer fuel economy variability

– Unlike engine and power-train test cells, no control of temperatures and 

pressures

 Coolant temperature

 CAC outlet temperature

 Inlet restriction

 CAC delta p

 Exhaust restriction

• Steps to decrease variability

– Drive by wire

– Engine clutched fan

– External compressed air supply
Drive by Wire

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• Light-duty colleagues were using method first

• Adopted to HD use early 2014

– Use only with automatic, or automatic shifting manual transmissions

• GEM driver model for control

– Immediate benefits

 Improved FE COV, very little pedal variation

300 310 320 330 340 350 360 370 380 390 400

Time (s)

Throttle Position - ARB Cycle

Drive by Wire

Drive By Wire

Drive by Wire

Human Driver

Human Driver
Clutched Fan Control

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• Disable the clutched fan or control fan to engage same time, 

and duration during each cycle

• Minimal change at engine idle speed

• Significant change at higher engine speeds

0.6

2.4

4.4

9.8

17.8

0

2

4

6

8

10

12

14

16

18

20

600 900 1200 1500 1800

Power (kW)

Engine Speed (RPM)

Fan Absolute Power – Zero Vehicle Speed

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Air Compressor Control

• EPA requested an analysis of air compressor impact on transient 

cycles

– Supply shop air to onboard tanks to prevent operation

• Air compressor impact hidden by variation of driver

20

720

740

760

780

800

820

840

860

880

900

Tank Pressure (kPa)

Air Compressor Characterization - ARB Cycle

Driver ARB 1

Driver ARB 2

DBW - Tank Pressure

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Heavy Duty Chassis Dyno

Closing Statements

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Summary of Testing

• Transit Bus

• F650

• Freightliner Cascadia

• Kenworth T700

• Kenworth T270 Box Truck

• Autocar Refuse Hauler

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Conclusions

• Heavy Duty Chassis Dyno capable of testing all wheel 

drive vehicles, all the way up to class 8 vehicles

• 40CFR 1066 Compliance

• Current program goals provided opportunities to 

improve operation of heavy duty chassis dyno

• Variability mitigation in the form of “robot” driver, 

clutched fan control, and air compressor control

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Questions?

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