# Powertrain vs. Chassis Dyno and their Variability Discussion

Southwest Research Institute 10

- Dec

- 2014

12 

# Introduction

• Comparison of powertrain testing and chassis testing

• Sources of chassis test result variation

– Driver Behavior



# – Thermal Management

– Roll friction uncertainty

• Chassis test cell configuration improvements 

# to mitigate sources of test results variability 0 5 10 153 

# Chassis Dynamometer Facility Compared To Powertrain Test Facility

Cons

• Large facility required for full vehicle

• Climate control for entire test cell

• Road speed fan Pros

• Convenient vehicle evaluation

• Does not require OEM support to operate a powertrain in a vehicle

• Correct packaging and heat transfer4 

# Powertrain Test Facility Compared To Chassis Dynamometer Facility

Cons

• Questions about representative packaging and heat transfer

• Requires engine and transmission control integration



### • Difficult to include systems that may require power through the wheels, i.e. regenerative braking. Pros

• Uses existing engine test cell 

### equipment

• Easier to simulate different vehicle configurations

• Easier to control5 

# Key Differences Between Chassis Testing and Powertrain Testing

Engine Trans Driveline Wheels Torque

Speed

T 1 Physical

Inertia, friction Dyno

- Set simulated inertia, road load T 2

Cut

Engine Trans Driveline Wheels Torque

Speed

T 1 Physical

Inertia, friction Simulated inertia, road load T 2

Cut Chassis dynamometer includes,

Powertrain testing does not

Both simulate some inertia and road load forces6 

# Powertrain Test Cell Operation

Pedal Position (Torque Command)

Vehicle Software Models

Dyno Motor Speed Control

Driveshaft Torque/Speed Feedback Driveshaft

Speed Command

Drive Cycle

(Vehicle Speed vs. Time) Driver7 

# Conventional HD Chassis Implementation

Pedal Position (Torque Command)

Dyno Motor

Vehicle Speed Feedback Vehicle

Speed Command Target Cycle Speed

Vehicle

Software Model Drive Cycle (Vehicle Speed vs. Time)

Roll Torque Measurement

# Driver Behavior

8

# Two Examples of Driver Behavior 

# Influencing Fuel Economy

• Transmission gear selection

• Thermal management

9Uncertainty interval of plus

- minus two standard errors.

10 

# Average Fuel Economy of Powertrain Cell Tests Compared to the Chassis Dynamometer Tests

1.5% 2.2% 3.8% 2.4% 6.0% 3.0%

0 0 0 0 0 0 0

4 6 8 10 12 14 16 18

55 MPH 65 MPH ARB Transient WHVC CILCC Parcel Fuel Economy, MPG Chassis
Powertrain
% Diff Steady

- state driveshaft power match The primary source of error is described in the following slides11 

# Different Driving Behaviors Produce Different Fuel Economy Results12 

# Different Driving Behaviors Produce Different Fuel Economy Results

- Cont’d13 

# Different Driving Behaviors Produce Different Fuel Economy Results

- Cont’d

# Thermal Management

Variability

14

# Impact of Thermal Management on Fuel 

# Economy for

- 15% C rr

• Occurs from ~180 sec to ~320 sec

• Duration of thermal management modes categorized as,

– Critical

– Moderate

– Minimal



### • Fuel economy reduced by 1.8% with each successive degree of thermal management

15

# Thermal Management for EPA Optimized Case

16

# Sources of Variation of Thermal 

# Management

• Most of the variation is due to variable soak times.

• When soak times are longer than 20 minutes, the thermal management time is typically longer.



# • Driver behavior contributes to thermal management variation. If the driver is aggressive, the engine produces more heat in 

# the exhaust and less thermal management at idle is required.

17

# HD Chassis Dynamometer

Tire Friction

18

# Experiments Conducted on HDC with Box 

# Truck

10

- Dec

- 2014 19 

# Three different experiments were conducted 

# with the box truck installed on the HDC

Day 1

– Constant speed with and without the driveshaft installed at 45 mph, 55 mph, and 65 mph

Day 2

– Repeat of Day 1, but at speeds from 5 mph to 65 mph in 5 mph increments

Day 3

– Recorded tire pressure and temperature cold, then warmed up 

### the tires by motoring at 45 mph with driveshaft installed and engine running

# Friction measured at Constant Speed on 

# Different Days

10

- Dec

- 2014 20 From two different runs on different days, the friction force varies up to 3% of the total road load force at constant speed.

# Friction as a Function of Tire Temperature 

# and Pressure at 45 MPH

10

- Dec

- 2014 21 ~270 N after 30 min. from cold

Average Tire Temperature Change = 9.7 degC Average Tire Pressure Change = 45 kPa

# Test Result Variation

Comparison of Different HDC 

# Configurations

2223 

# Conventional HD Chassis Implementation

Pedal Position (Torque Command)

Dyno Motor

Vehicle Speed Feedback Vehicle

Speed Command Target Cycle Speed

Vehicle

Software Model Drive Cycle (Vehicle Speed vs. Time)

Roll Torque Measurement24 

# Experimental HD Chassis Implementation

Pedal Position (Torque Command)

Dyno Motor

Vehicle Speed Feedback Vehicle

Speed Command Target Cycle Speed

Vehicle

Software Model Drive Cycle (Vehicle Speed vs. Time)

Driveshaft Torque Measurement Driver Software Model

Eliminates Friction Estimation Uncertainty Provides consistent, predictable driver behavior

# HDC Test Results Variation For Various 

# Vehicles and Varying HDC Configurations

10

- Dec

- 2014 25 High test weight, using driveshaft torque meter to control roll speed & powertrain driver model

Test weight closest to dyno roll inertia, human driver

Medium test weight, human driver
Highest test weight, human driver

### • From our studies at SwRI:

• 1. Driver characteristics RANK 1 (most important)

• 2. Aftertreatment thermal management differences between chassis and powertrain testing

• 3. Dyno

- to
- dyno control and response differences

• 4. Heat exchanger behavior

• 5. Modeling of driveline characteristics



## • We are continuing to refine our test procedures to improve accuracy and precision.

26 

# Summary