Duty Cycles, Standardisation and Validation of

Low Carbon Power Systems

Prof. Richard Stobart and Dr. Rui ChenDepartment of Aeronautical and Automotive Engineering

Loughborough University

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Contents:

1. Motivation

2. Driving Cycles

3. Low Carbon Power Systems

4. Driving Cycle Impact

5. Real World Results

6. Criteria and Methodology of Cycle Selection

7. Case Study

8. Real World Strategy of HEVs

9. Conclusions

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1. Motivations

Many anecdotal reports from HEV owners that in-use fuel economy does not match the authority’s estimates.

Fuel economy benefits of a hybrid vehicle are highly dependent on: Vehicle duty cycleComponent performanceIntegration and control of the powertrain and vehicle systems

To help avoid this problem, the vehicle could be designed with considering all-electric range operation on more aggressive driving cycle or “real-world” driving cycle.

Such a consideration, however, would lead to even larger or costlier electric motor and energy storage system (ESS) requirements.

There is a need of more realistic Duty Cycles for Standardisation and Validation of Low Carbon Power Systems.

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2. Driving Cycles

A driving cycle is a standardised driving pattern described by means of a velocity-time table.

The world-wide used driving cycles can be divided into three groups:

European driving cycles - These belong to the modal cycles, which means there are parts in these cycles where the speed is constant.

ECE 15, EUDC, EUDCL, NEDC, HYZEM, etc.

US driving cycles - These driving cycles belong to the transient cycles and give a better representation of real driving patterns than the modal cycles.

FTP 72, SFUDS, FTP 75, HFEDS, IM 240, LA-92, NYCC, US 06, etc.

Japanese driving cycles - belong to the modal cycles.10 Mode, 15 Mode, 10-15 Mode, etc.

NEDC

FTP 72

10-15 mode

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3. Low Carbon Power Systems

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HEVs Control Strategies:

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Characteristics of an Individual Pulse Power Event:

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Two Modes Control Strategies:

Engine Minimum Assistance Logic -The vehicle operates all-electrically until the driving demand exceeds the power capability of the electric machine.

Engine Assistance at Best Efficiency Logic - the engine is also turned on when the electric motor power reaches its maximum power curve but the engine now operates close to its best efficiency curve. The surplus power from the engine is used to charge the battery.

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4. Driving Cycle Impact

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Engine Minimum Assistance:

Source: J. Kwon, J. Kim, E. Fallas, S. Pagerit and A. Rousseau, Impact of Drive Cycles on PHEV Component Requirements, SAE 2008-01-1337

The average electric machine power is much higher (65 to 45 kW) for the US06 than for the Urban Dynamometer Driving Schedule (UDDS)

Comparison of Motor Power Distributions between driven on UDDS and US06 (10AER)

Comparison of Engine Power Distributions between driven on UDDS and US06 (10AER)

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Engine Assistance at Best Efficiency:

Source: J. Kwon, J. Kim, E. Fallas, S. Pagerit and A. Rousseau, Impact of Drive Cycles on PHEV Component Requirements, SAE 2008-01-1337

Component Sizes over Various DrivingCycles (10AER)

Usable Energy of the Battery Based on Various Driving Cycle (10AER)

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HEV Component Sizing:

Charge-Depleting (CD) Vs. Charge-Sustaining (CS) Modes

Component Sizes over UDDS Total Battery Energy over UDDS

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HEV is more sensitive to driving cycle:

Argonne study demonstrated HEV’shave higher fuel consumption sensitivity to aggressive driving

Source: Phillip Sharer, Romain Leydier, AymericRousseau, Impact of Drive Cycle Aggressiveness and Speed on HEVs Fuel Consumption Sensitivity, Argonne National Laboratory, 2007

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5. Real World Results

Baseline Performance Testing Fuel Economy Decrease Using Air Conditioning

Source: US Department of Energy Hybrid Electric Vehicle Battery and Fuel Economy Testing, by Donald Karnera, James Francfortb

HEV end-of-life fuel economy test results

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6. Criteria and Methodology of Cycle Selection

The cycle must be supported by the involved OEM, hybrid electric system supplier, and end-user.

The vehicle must be able to meet the cycle speed trace with reasonable accuracy (+/- 2 mph).

The cycle should represent typical customer driving patterns HEVs.

The cycle should be easy to execute for chassis dynamometer and vehicle field tests, allow SOC correction for charge-sustaining HEVs, and be suitable for fuel economy and emissions testing.

GOAL OF CYCLE SELECTION : to provide an objective drive cycle tobenchmark the HEV’s benefits and tradeoffs.

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7. Case Study - Composite Cycle for Heavy-Duty HEVs

The goal was to provide an objective drive cycle to benchmark the Class 4-6 heavy-duty HEV’s benefits and tradeoffs.

The difference between the initial and final state of charge (SOC) of an HEV’senergy storage system can significantly affect measurement of fuel economy.

In addition to representing real-world driving patterns, the effect of start/end SOC change on fuel economy measurement was considered when evaluating drive cycles.

To develop a representative drive cycle that is relatively insensitive to SOC correction, three different types of drive cycles were considered: element, weighted, and composite cycles.

Source: Zhanjiang Zou, Scott Davis and Kevin Beaty, Michael O'Keefe, Terry Hendricks and Robert Rehn, Steve Weissner and V. K. Sharma, A New Composite Drive Cycle for Heavy-Duty Hybrid Electric Class 4-6 Vehicles, SAE 2004-01-1052

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Types of Available Drive Cycles:

ELEMENT CYCLE - is a standard speed-versus-time trace such as those found in the literature and industry standards.

WEIGHTED CYCLE - includes individual city, suburban, and highway cycles. Vehicles are tested over the individual cycles separately. Combined fuel economy is calculated based on fuel consumption over each individual cycle and weighting of the cycles, as shown in the following equation:

COMPOSITE CYCLE - A composite cycle combines various driving patterns into one cycle.

Example of a Composite Cycle Consisting ofTwo UDDS cycles and one HWFET cycle

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Candidate Composite Cycles:

Composite Cycle 1 - consists of three CBDTRUCK cycles (Geometric cycle representative of city heavy vehicle mission.), two ARTERIAL cycles, and one COMMUTER cycle

Composite Cycle 2 (CILCC) - the Combined International Local and Commuter Cycle (CILCC) - consists of four International Local cycles and one shortened COMMUTER cycle

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Evaluating Candidate Cycles Based on Driving Patterns:

Average Speed and Stops per Mile of Candidate Drive Cycles Compared with TargetThe CILCC meets all the criteria established for selecting a drive cycle.

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Results:

Fuel Economy Gain of the Class 5 HEV over Various Drive Cycles

Customer-Reported Driving Pattern for Class 4-6 Pickup and Delivery Trucks

Characteristics of CILCC

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Case Study - Honda Ecological Drive Assist System

The system combines three functions to enhance fuel economy:

the ECON Mode utilizes harmonized control of the continuously variable transmission (CVT) and engine to support more fuel-efficient driving;

the guidance function uses speedometer colour to provide real-time guidance on fuel-efficient driving; and

The scoring function provides feedback about current driving practices, as well as feedback on cumulative, long-term fuel-efficient driving.

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8. Real World Strategy of HEVs

Factorisation of Real World Driving for Minimising Vehicular CO2Emissions

Objectives:Powertrain Systems Analysis Model of optimised driving behaviour Real world driving data analysisFactor analysis using Singular Value Decomposition (SVD) to decompose the difference between real world and the optimised modelFactor classification, driver dominated factors or vehicle system dominated factors

Potential Deliverables:Develop suitable driving cycles for standardisation and validation oflow carbon power systemsOptimise driver dominated factors to improve / correct driving behaviourOptimise vehicle system dominated factors to improve vehicle design and control algorithm

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9. Conclusions

The choice of driving cycles influences HEV design decisions.

All standard drive cycles considered are less aggressive than real-world driving conditions.

New drive cycles developed in the future should be more representative of real world driving patterns.

The new drive cycles should also address the test drive cycles for local and national driving patterns.

Factorisation of real world driving has a potential to develop suitable driving cycles and minimise vehicular CO2 emissions.

THANKS FOR ATTENTION

Questions?