Technical Targets

The objective of technical target setting is to identify and quantify vehicle, subsystem, and component-level research and development technical targets that will enable industry to meet the goal of the Advanced Heavy Hybrid Propulsion System (AH²PS) project—to double the fuel economy of a commercially viable vehicle. As many combinations of technical targets could enable us to meet our goals, NREL is seeking the solution that has the lowest associated R&D effort and life cycle cost.

Researchers at NREL are working with AH²PS industry teams to identify heavy hybrid vehicle system requirements with a cascading approach to set technical targets (Figure 1). The AH²PS project has goals for vehicle-level performance, cost, and reliability requirements. These requirements are cascaded down to the vehicle powertrain and component level and technical targets are set within commercial viability constraints. Thus, a given set of targets will be vocation specific and linked back to an actual vehicle system.

Cascading diagram depicting the vehicle requirements used to set technical targets for AHHPS. We must ask the question of whether the current technology using existing commercial constraints of vehicle level performance, cost, and reliabiliy requirements, allow us to meet our goals and if not these are the factors we use to set technical targets. These targets are cascaded down to the vehicle powertrain and component levels and technical targets are set within these commercial viability constraints.

Figure 1 - Cascading of vehicle requirements to set technical targets

The Process

The heavy hybrid technical target setting process is structured around the following questions:

Where are we now?
Where do we want to go?
How will we get there?

NREL's AH²PS team seeks to understand commercial viability constraints, duty cycles, and fuel consumption patterns. The lower left side of Figure 2 shows baseline vehicles and depicts where we are. The goal—to double fuel economy—is in the upper right corner and depicts where we want to go.

To reach our goal, we need to develop and optimize heavy hybrid technology. However, the limitations of presently available technology may prevent us from reaching our goal. At this point, we must ask the three questions again. The target setting process addresses how we will get there by setting R&D technical targets on critical component- and system-level needs that will bridge the gap between where we can get to today and where we want to be as a result of the AH²PS project.

Diagram of the Technical Target Setting process used by AHHPS to determine how various technologies based on the following constraints- cost, reliability, product viability, performance, and manufacturability affect fuel efficiency in Class 7-8 vehicles. Within the constrants of commercial viability, it is unlikely that we will be able to meet our program goal of 2x with present technology. Therefore, we use target setting as a means to delvelop future components that bridge the gap.

Figure 2 - Progression toward the AH²PS goal

AH²PS team members focus on understanding the numerous technological pathways and examining how to bridge the gap between present status and future goals. We can improve fuel economy with any one of several steps, including:

Reduce weight
Increase peak engine brake thermal efficiency
Electrify auxiliary loads
Improve braking regeneration
Reduce energy storage losses
Increase motor/power electronic efficiencies
Reduce aerodynamic drag
Reduce tire rolling resistance

Other improvements to component cost and reliability may increase the commercial viability and market penetration of heavy hybrids. However, starting an R&D program to improve a technology metric within a given time frame will require funding that will depend, in part, on the aggressiveness of the goal.

The funding level to DOE represents a cost function that we would like to minimize computationally (see Figure 3). We must:

Identify the metrics (drivetrain efficiency, regenerative braking efficiency, auxiliary load reduction, etc.).
Quantify the metrics for present status and best future potential.
Find the cost function that measures the relative burden of improving one metric versus another.
Run these data in an optimization program to select the best combination of technical targets that meet all constraints and program goals with the least R&D cost.

Diagram depicting pathways for improving technology that allows the AHHPS project to meet both its commercial and technical (efficiency) goals. However, not all pathways are equal. As we advance a given attribute of a technology (e.g. an engine's peak thermal efficiency), we can incur a 'penalty'. This 'penalty' may be related to R&D spending required to achieve the given goal. The technical target setting process, used in the AHHPS project, sets targets that minimize the overall penalty incurred while meeting program goals (commercial viability and 2x fuel economy over a baseline vehicle).

Figure 3 - Optimization to minimize R&D cost while setting technical targets

Timing

NREL is working with AH²PS industry teams to identify these heavy hybrid technical R&D targets. Once identified, the targets will be transmitted to DOE so R&D programs can be initiated that will influence AH²PS Phase II.

Contact

For further information, contact:

Michael O'Keefe
AH²PS Heavy Hybrid Technical Target Setting Lead
Advanced Vehicles and Systems Group
Center for Transportation Technologies and Systems
National Renewable Energy Laboratory
1617 Cole Boulevard, MS 1633
Golden, CO 80401
e-mail: michael_okeefe@nrel.gov
phone: 303-275-4268

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