HD Chassis Testing Part 2 

Southwest Research Institute

10-Dec-2014

10-Dec-2014 1
Introduction

2

• HD chassis dynamometer challenges

• Heavy-Duty Chassis Dyno Sample Results

• Chassis dynamometer ‘Set’ coefficients

• Class 8 grade cycle findings

10-Dec-2014
SwRI HD Chassis Dynamometer (HDC)

3

Two 48-inch rolls

300 hp DC motor on each roll

250 hp road speed fan

10-Dec-2014
HDC Control Challenge vs. LD Chassis

4

Base 9,000 lb 

Min 1,000 lb 

Max. 8,000 lb 

Base 3,000 lb 

Max. 80,000 lb 

• HDC simulates much higher 

inertia values.

• HDC simulates a wide range of 

inertia values

Typical vehicle test inertia values 

for each chassis dyno

10-Dec-2014
Comparison of Load Requirements

5

-15000

-10000

-5000

0

5000

10000

15000

0 100 200 300 400 500 600 700 Dynamometer Roll Torque, [N-m]

Time, [seconds]

Control torque HDC Nm

Control torque LDC Nm

HDC simulates

~20x more load

than LDC

10-Dec-2014
Heavy-Duty Chassis Dyno 

Sample Results

7/6/2015 6
F650 Tow Truck

7/6/2015 7

• Chassis dyno testing

– ARB Transient

– WHVC

– Parcel

– 55 mph & 65 mph steady state

2012 Ford F650

– Cummins ISB 6.7L engine

 240 HP

– Allison RDS2200 5 speed automatic transmission
F650 Tow Truck

7/6/2015 8

14.75

11.99

9.90

12.38

7.06

9.58

4

6

8

10

12

14

16

55 MPH 65 MPH CARB Transient WHVC Parcel Utility

Cycle Average Fuel Economy (mpg)

Standard Cycle Fuel Economy Results
Transit Bus

7/6/2015 9

• Chassis dyno testing

– ARB Transient

– WHVC

– Parcel

– CILCC

– EPA City Bus Cycle

– 55 mph & 65 mph steady state

2012 New Flyer Urban Transit Bus

– Cummins ISL 8.9L engine

 280 HP

– Voith D864.5 automatic transmission
Transit Bus: Chassis Dyno Results

7/6/2015 10

8.49

6.42 6.19

7.51

4.32

6.74

2.88

0

1

2

3

4

5

6

7

8

9

10

55 MPH 65 MPH CARB Transient WHVC Parcel Utility EPA Bus Cycle

Cycle Average Fuel Economy (mpg)

Standard Cycle Fuel Economy Results
Chassis dynamometer ‘Set’ 

coefficients

10-Dec-2014 11
Box Truck

7/6/2015 12

• Chassis dyno testing

– ARB Transient

– WHVC

– Parcel

– CILCC

– 55 mph & 65 mph steady state

– Test Matrix (All cycles with 6 

different parameter variations) 2012 Kenworth T270 Box Truck

 240 HP Cummins ISB 

– Allison automatic transmission
Dynamic Road Load Force

10-Dec-2014 13

Engine Trans

Steer tire friction Drive tire friction

Aerodynamic friction

Transmission output 

shaft friction

Bearing & FD friction

(from all axles)

Dynamic Road Load Force = Friction(Steer tire & bearings+ Transmission output shaft + Drive tire & bearings) 

+ Aerodynamic friction
Determination of Dyno ‘Set’ Coefficients

10-Dec-2014 14

Engine Trans

Drive tire, bearing & FD

friction

Steer tire friction

Aerodynamic friction

Transmission output 

shaft friction

Dyno ‘Set’ Coefficients= Friction(Steer tire & bearings) +

Aerodynamic friction

Difference between GEM Road Load Force and HDC Road Load Force =

Friction(Transmission output shaft + Drive bearings+FD )
Driveshaft Friction as a Function of Speed

10-Dec-2014 15

0

200

400

600

800

0 5 10 15 20 25 30

Friction Force [N]

Vehicle Speed [m/s]

With DS

Without DS

Fitted Difference
6

7

8

9

10

11

12

13

0 1 2 3 4 5 6 7 Fuel Economy [MPG]

HDC

GEM Driveline Friction Included

GEM Driveline Friction Removed

GEM vs HDC With and Without Driveshaft 

Friction Included in Road Load Force

10-Dec-2014 16

7.0%

6.3% 3.3%

4.4%

3.5% 1.3%

55 mph 65 mph 

ARB 

Transient 

Parcel Utility WHVC 

Improved HDC correlation 

within 5% of GEM values 
Class 8 Grade Cycles

10-Dec-2014 17
Road Grade Measurement

• SwRI used an 

autonomous vehicle 

equipped with high 

resolution GPS and 

grade inclinometer 

to measure road 

grade.

7/6/2015 SwRI/US EPA Confidential 18
150 151 152 153 154 155 156 157 158 159 160

0

5

10

15

20

25 Fuel Rate (g/s)

Cumulative Distance (km)

150 151 152 153 154 155 156 157 158 159 160

-5

-4

-3

-2

-1

0

1

2

3

4

5

 0.08 km Window

 0.16 km Window

 0.40 km Window Grade (%)

Cumulative Distance (km)

Determination of Road Grade

SwRI created software to align grade 

measurement with vehicle fuel rate data.
Fuel Economy Evaluation of Grade

10-Dec-2014 20

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

0 100 200 300 400 500 600 700 800 900

Time (sec)

Grade [%] 75 mph

Grade [%] 65 mph

Grade [%] 55 mph

• 20 km segment was taken from on-highway 

testing (~75 mph)

• 55 mph and 65 mph input grades were then 

generated based upon this data
Evaluation of Grade

10-Dec-2014 21

• Results showed that inputting grade yielded 

high fuel economy.

• However this was due to an overall downhill 

effect!

-25

-20

-15

-10

-5

0

5

-2

0

2

4

6

8

10

12

14

16

18

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

Cum Grade [%]

Cum CO2 [kg]

Time [sec]

1121 Cum CO2

1122 Cum CO2

1121 Cum Grade
Evaluation of Grade

10-Dec-2014 22

• An offset was imposed to achieved zero grade 

overall

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

-3

-1

1

3

5

7

9

0 100 200 300 400 500 600 700 800 900

1121 Grade

1129 Grade

1121 Grade Cum

1129 Grade Cum
Evaluation of Grade

10-Dec-2014 23

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

3

0

10

20

30

40

50

60

70

80

90

-50 50 150 250 350 450 550 650 750 850

Grade

Fuel Rate

Time (sec)

1129 Fuel Rate

1129 Grade
Class 8 Tractors Tested Over Grade Cycles

24

Kenworth T700 AMT

10-Dec-2014

Freightliner Cascadia Manual
Grade Characterization: Conclusions

• “Light” truck test weight 3460 kg lighter than “Heavy” 

truck. Weights were chosen independently for 

different purposes.

• Road load force of Light truck vs. Heavy truck:

– 14% lower at 65 MPH

– 16% lower at 55 MPH

• Total force of Light truck compared to Heavy truck:

– 25% lower at 65 MPH

– 27% lower at 55 MPH

10-Dec-2014 25
Road Load Force For Light & Heavy Trucks

26

0

1000

2000

3000

4000

5000

6000

0 10 20 30 40 50 60 70 80

Force (N)

Speed (mph)

Road Load - Force vs Speed

• Road load based on coastdown coefficients

10-Dec-2014

Heavy

Light
Grade Force for Light and Heavy Truck

27

-8000

-6000

-4000

-2000

0

2000

4000

6000

8000

10000

0 100 200 300 400 500 600 700

Force (N)

Time (s)

Heavy

Light

10-Dec-2014
Fuel Consumption Compared to Grade

28

-10

0

10

20

30

40

50

60

70

0 100 200 300 400 500 600 700 800 900

(m3/hr)

55 MPH Baseline

55 MPH Grade

Grade

10-Dec-2014
Grade Effect on Fuel Economy

29

10%

4.1%

8.9%

1.6%

5.5

6

6.5

7

7.5

8

8.5

9

9.5

10

T700 - 55 MPH Cascadia - 55 MPH T700 - 65 MPH Cascadia - 65 MPH

Baseline

Grade

Heavy - 55 mph

Smaller difference between grade 

and no grade

10-Dec-2014

Light - 55 mph Heavy - 65 mph Light - 65 mph
Class 8 Operation over Grade

30

52

53

54

55

56

57

58

59

0 100 200 300 400 500 600 700 800 900

Speed (mph)

Time (s)

Downshifts

Heavy

Light

• Light truck does not need to shift to maintain 

speed at 55 MPH.

• The result is better fuel economy and less delta 

between grade and no grade cycles.

10-Dec-2014
Vehicle Speed Difference – 65 MPH Grade

Light vs. Heavy

31

• Rapid change in vehicle speed and torque demand of Heavy 

truck due to weight and road load coefficients

• Result is worse fuel economy, and high delta between grade 

and no grade 

62

63

64

65

66

67

68

0 100 200 300 400 500 600 700 800

Speed (mph)

Time (s)

10-Dec-2014

Heavy

Light
Summary of Grade Results

• Light vs. Heavy Truck Discussion:

– The Light did not downshift because the 

lighter load did not require as much power.

– By remaining the same gear throughout the 

grade cycles, the fuel economy of the Light 

truck was not impacted by grade as much as 

the Heavy truck.

10-Dec-2014 32
Summary

33

• HD chassis dynamometer testing is difficult

• Multiple vehicles were tested on a HD chassis 

dyno

• Transmission output shaft torque is a 

significant load and must be considered during 

coastdowns

• Influence of grade on fuel economy is a 

function of vehicle weight, road load, shift 

schedule

10-Dec-2014