# HD Chassis Testing Part 2

Southwest Research Institute 10

- Dec

- 2014

1 10

- Dec

- 2014

# Introduction

2 

# • HD chassis dynamometer challenges



# • Heavy
- Duty Chassis Dyno Sample Results

• Chassis dynamometer ‘Set’ coefficients

• Class 8 grade cycle findings

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- 2014

# SwRI HD Chassis Dynamometer (HDC)

3 

# Two 48
- inch rolls 300 hp DC motor on each roll 250 hp road speed fan

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- 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

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- 2014

# Comparison of Load Requirements

5 

# HDC simulates ~20x more load than LDC

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- 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

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- 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

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- 2014 13 Engine Trans

Drive tire friction Steer tire friction Aerodynamic friction

Transmission output shaft friction Bearing & FD friction (from all axles)



### Dynamic Road Load Force = Friction(Steer tire & bearings+ Transmission o utput shaft + Drive tire & bearings) + Aerodynamic friction

# Determination of Dyno ‘Set’ Coefficients

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- 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 Forc e and HDC Road Load Force = Friction(Transmission output shaft + Drive bearings+FD )

# Driveshaft Friction as a Function of Speed

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# GEM vs HDC With and Without Driveshaft 

# Friction Included in Road Load Force

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# 7.0% 6.3% 3.3%



# 4.4% 3.5% 1.3%

55 mph 6 5 mph ARB Transient Parcel Utility WHVC Improve d HDC correlation within 5% of GEM values

# Class 8 Grade Cycles

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- 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

# Determination of Road Grade SwRI created software to align grade measurement with vehicle fuel rate data.

# Fuel Economy Evaluation of Grade

10

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- 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

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- 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

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# • 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

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- 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

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- 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

25 10

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# 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

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## 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

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# 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 (m 3 /hr) 

## 55 MPH Baseline
55 MPH Grade
Grade

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# 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

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- 2014 

## Light
- 55 mph Light
- 65 mph Heavy - 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.

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# 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)

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## 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.

32 10

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- 2014

# 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

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- 2014