Innovators at NASA’s Glenn Research Center have developed an automated pulse-and-glide technique using a flywheel energy storage system for on-road vehicles; the technology, which NASA Glenn says can improve fuel economy over existing internal combustion or battery hybrid systems by 40-100%, is available for licensing.
Drivers can use a manual “pulse-and-glide” (PnG) driving technique—accelerating and decelerating an automobile in cycles of approximately 10-30 seconds—as a way to improve fuel economy. A 2009 SAE paper by a team from Virginia Tech and Argonne National Laboratory found that a simulated PnG driving strategy in a Ford Focus delivered 33-77% fuel economy improvement depending on different speed ranges and acceleration times. The fuel economy results of a 2004 Toyota Prius from simulation and testing showed 24-90% fuel economy improvement with PnG drive cycles compared to steady speed results.
The downside of such a technique is that it currently requires sustained attention from the driver. (Further, noted Lee et al. in their 2009 study, a driver in a conventional vehicle must shut off the engine manually to apply this strategy optimally.)
NASA Glenn says that its automated pulse-and-glide flywheel presents an economical, reliable, and long-term solution for a significant improvement in fuel economy performance without requiring driver intervention. Unlike chemical batteries, which also have a short life span and high replacement costs, flywheels provide the power and energy requirements necessary for a robust pulse-and-glide technique, the researchers said.
The flywheel PnG system delivers power and energy between 8-20 kilowatts (kW) and 2-3.5 kilowatt hours (kWh); system lifetime is approximately 10 years.
NASA says that it is seeking a patent on the technology.
NASA is not alone in its current interest in expanding the use of automated PnG capabilities. As one example, in February, Ford Motor Company filed a patent application on technology developed by researchers in the UK for leveraging the pulse-and-glide approach in engine control to maximize fuel economy.
The approach in essence allows small variations in vehicle speed around the threshold speed in order to operate at or close to the optimal BSFC. Using the pulse and glide approach, the vehicle speed will have a mean value around the threshold speed, but the fuel consumption will be reduced in comparison to a constant fueling regime.
As another example, in 2012, Volvo Car Corporation filed its own patent on a new controls-based way to utilize the “pulse and glide” technology not only in coast mode but also in normal driving conditions.
US Patent Application Nº 20130226420: Vehicle Speed Control Apparatus And Method
EP 2476572 A2 Method for speed control, speed control system and device for use with the speed control system
Lee, J., Nelson, D., and Lohse-Busch, H. (2009) “Vehicle Inertia Impact on Fuel Consumption of Conventional and Hybrid Electric Vehicles Using Acceleration and Coast Driving Strategy,” SAE Technical Paper 2009-01-1322, doi: 10.4271/2009-01-1322