TransForum Vol. 8, No. 2

Impact of Drive Cycles on PHEV Component Requirements

Component Sizes Over Various Driving Cycles

Usable Energy of the Battery on the Basis of Various Driving Cycles

Argonne researchers led by Aymeric Rousseau recently studied the impact of drive cycles on the component requirements of plug-in hybrid electric vehicles (PHEVs). Results showed that vehicles designed to satisy the urban dynanometer driving schedule (UDDS) may fail to achieve all-electric-range (AER) for real word driving (i.e., the modeled PHEV used more engine energy as driving cycle aggressiveness increased). As a result, drivers would not be able to drive in all-electric mode and would have to start the engine earlier than expected. The results were presented in April at the Society for Automotive Engineers 2008 World Congress.

The Powertrain Systems Analysis Toolkit (PSAT), a software package that simulates fuel efficiency and performance of advanced powertrains, was used for the evaluation. Modeling a midsize pre-transmission parallel hybrid, the researchers studied the sensitivity of driving distance and energy consumption vs. driving cycle aggressiveness. The UDDS and six additional standard driving cycles were assessed.

Researchers Rousseau, Jason Kwon, Jeongmin Kim, Eric Fallas and Sylvain Pagerit evaluated the consequences of sizing the electrical machine and battery power to follow the UDDS and determined the number of other standard driving cycles that can be followed in electric vehicle mode. They then studied the impact of sizing the electrical components on other driving cycles. Two control modes were used. In “Engine Minimum Assistance” mode, the vehicle operated all-electrically until driving demand exceeded battery power alone and the engine provided only the additional power. In “Engine Assistance at Best Efficiency” mode, the engine was operated close to its best efficiency.

The study showed that:

• The choice of driving cycle directly influences decisions on PHEV design. A PHEV is sensitive to increased cycle aggressiveness and driving range because it will be unable to satisfy significant power demands during charge depleting (CD) mode, all electrically as designed.
• When assistance from the engine is necessary, the engine assistance at best efficiency strategy has an advantage in terms of improving driving range and lowering energy consumption of the designed PHEV. However, this strategy increases the charge depleting range, which may lead to the battery not being fully discharged at the end of a trip, thus decreasing fuel efficiency.
• A PHEV sized on the basis of aggressive driving cycles requires larger and more expensive electric components but offers AER operations, the benefits of which include qualifying for greater credits toward satisfying California Air Resources Board’s zero-emission vehicle regulation and a smoother-driving quality.

A complete copy of this conference paper can be obtained by ordering it from SAE at https://shop.sae.org/congress/2008/. Select “Technical Papers,” and then “Systems and Components.”

This research was supported by DOE’s Vehicle Technologies Program under the direction of Lee Slezak.

November 2008