Enova Offering its Hybrid Drive Systems for OEM or Retrofit Applications with Plug-In Option

11 September 2006

Enova Systems has announced that its most recent commercial awards will be completed with the company’s Post-Transmission Parallel Hybrid Drive System, available with either charge-depleting or charge-sustaining (i.e., plug-in) battery technology. Enova expects the technologies to improve fuel economy up to 100%.

The recently announced hybrid school bus from IC Corporation is based on an Enova post-transmission system, for example, and offers a plug-in hybrid configuration. (Earlier post.)

Our unique Post Transmission System offers OEM (Original Equipment Manufacturers) customers a non-invasive solution to enter the Hybrid Vehicle Market in either the retrofit or new vehicle segment. Enova’s Post Transmission System is comprised of our proprietary AC induction electric motor, controller and energy management system, and is designed and engineered as a total production ready solution. Being the only supplier of this technology offers us and our customers a tremendous competitive advantage

—Mike Staran, Enova Vice President of Marketing

The electric drive system in the post-transmission system is integrated behind the transmission and is designed to be fully integrated into an OEM production line, or retrofitted in post-vehicle production in a modular, as-needed basis.

The charge-sustaining system utilizes relatively small batteries which are maintained within specified range of State of Charge (SOC) over the entire drive cycle. Battery charge is maintained by the on-board equipment (e.g., through regenerative braking) and is not normally recharged from the grid except as needed for cell balancing.

The charge-depleting (plug-in) system uses a larger battery based on advanced battery chemistry (NiMH or Li-ion—the hybrid school bus plug-in configuration uses an NiMH battery pack) that provides stored energy intended to be drawn down over the driving cycle, thereby optimizing fuel economy, subsequent to an overnight charge.

Enova is delivering a blended design for a plug-in hybrid (PHEV), rather than one that optimizes for all-electric range. In a blended system, the motor and engine work together from the start, with the engine turning on when power requirements exceed battery power capability—essentially, a beefed-up Prius model.

In a all-electric design, the vehicle functions initially just as an all-electric vehicle, and the engine turns on only when the battery reaches the low state of charge specified by the operating strategy.

Operation under an all-electric design.	Operation under a blended design.
Click diagrams to enlarge. Source: Tony Markel and Andrew Simpson (NREL), AABC-06, 19 May 2006

A blended design requires a smaller battery pack than an all-electric range (AER) design, thereby reducing cost, mass and volume, while still providing a strong fuel-consumption benefit. (Earlier post.)

Comparing PHEV battery sizing requirements for different designs. Source: Tony Markel and Andrew Simpson (NREL), AABC-06, 19 May 2006

Depending on the route, fuel economy miles per gallon (mpg) improvement is from 30% to 55% or better for a post-transmission charge-sustaining system, and 70-100% or better for post-transmission charge-depleting systems, according to Enova.

Emission improvements vary with the pollutant being measured and has shown up to a 90% improvement at times on Particulate Matter based on load and operating condition dependent.

In addition to the hybrid school bus with plug-in models, Enova also recently closed a contract to integrate service vans for a major North American fleet operator.

Resources:

• Battery Choices for Different Plug-in HEV Configurations (NREL)