Semi-OT:(Trinity Flywheel)Flywheels spin again
Although it has long been known that electromechanical flywheels have specific power ratings that far outclass those of electrochemical batteries and even the most efficient internal combustion engines, engineers have shied away from using them in automotive applica-tions. (The specific power of a device is the amount of power it can deliver per unit mass, which is usually measured in watts per kilogram.)
The two reasons most often cited are their insufficient specific energy (the amount of energy they can store per unit mass) for "pure" EVs—that is, for EVs powered solely by stored electrical energy and questions about their safety. Vehicle designers are concerned about a flywheel’s housing ability to contain the stored energy if the rotor should disintegrate or break free of its bearings.
Trinity Flywheel Power Inc., San Francisco, has produced one such "electrome-chanical battery" that it hopes will change those views. As part of a demonstration project sponsored by Weststart-Calstart, Alameda, Calif., an advanced transportation technology consortium, its mobile flywheel power module will soon be integrated with a hybrid electric power system developed by ISE Research Corp., San Diego, Calif., to power a mass transit bus.
The module, which sinks or sources power to a dc bus on demand, stores energy on two composite flywheel rotors that spin in opposite directions to negate the effects of gyroscopic torque. During charging, an on-board generator transfers electricity to the module, accelerating the rotors to as much as 48 800 rpm. On discharge, the unit acts as a variable-voltage, variable-frequency ac generator whose
output is converted to dc for driving the bus’s electric traction motors.
The 227-kg unit, which has a voltage range of 550—800 V, can assist the engine during acceleration or hill climbing by delivering a 750-kW (over a thousand horsepower) burst for 3 seconds or 200 kW for as much as 15 seconds. (Specific power is therefore 3300 W/kg.)
As for safety, Trinity believes it has the problem licked. "For years, the safety of flywheels has been a huge but vague concern," said Don Bender the company’s vice president of engineering. When asked whether a jolt from a bump in the road would knock the rotors free, Bender noted that their static gravitational force approaches 100 000 gn — far too high to be affected by shocks encountered during driving. Even if the rotors’ bearings should fail, Bender noted, a friction-based safety system designed to slow their rotation would kick in.
Trinity has already sold a power module to Hino Motors, Tokyo, the world’s leading producer of hybrid electric buses.
MICHAEL J. RIEZENMAN, Editor
With reporting by WILLIE D. JONES
Consultant: VICTOR WOUK, Victor Wouk Associates |
