THE FLYWHEEL BUS IS BACK

In the early 1950's, the well known Swiss engineering company Oerlikon introduced the "Gyrobus," a bus for 35 passengers that ran on electric power generated by a spinning flywheel, which was itself brought up to speed at points ½ mile apart by tapping the electric power net. The Gyrobuses were introduced in 1953 and remained in service (some of them in the Belgian Congo) for 10 years.

They were pushed out by diesel buses, which were not limited to a route with electrical tap points, nor forced to wait 1 to 2 minutes at each such point to recharge. Fuel cost was not a consideration at the time.

A four-year, $5 million contract for developing a flywheel bus was awarded to General Electric last year jointly by the Departments of Energy and Transportation.

The 1.5-ton flywheel will spin at 10,000 rpm, which gives it sufficient energy to move the 15-ton vehicle with its load of passengers 3.5 miles by using its 112 kW generator on the flywheel shaft. When its speed has dropped to 5,000 rpm, the driver pulls over to a charging point, where the generator, acting as a motor, will bring the flywheel up to full speed in 90 secs. When the driver accelerates, current is drawn from the generator on the flywheel shaft; when he brakes, the traction motor, acting as a generator, "recharges" the flywheel (accelerates it).

Development of the bus will involve GE's R&D Center at Schenectady, N.Y., its Transportation Systems Div. in Erie, Pa., and its Aircraft Group in Cincinnati, Ohio.

This type of bus has all the advantages of an electric trolleybus without the investment and maintenance of miles of overhead wires. The advantages over diesel buses are energy saving and reduced pollution. Compared with battery-driven vehicles, the flywheel buses can be "recharged" in 90 seconds, rather than many hours, and operated round the clock. Moreover, there is no need to replace expensive batteries; the service life of the flywheel bus should be similar to that of conventional buses.

The heart of the bus, the flywheel, runs in a sealed module containing low-pressure helium so as to minimize aerodynamic friction; if no current is drawn from the generator, the flywheel will spin for many hours.

A stack of steel disks weighing 1.5 tons and spinning at 10,000 rpm (167 revs a second!) is, of course, subjected to centrifugal stresses that could become dangerous if the disks were merely bolted together. They will therefore be "inertia-welded" by a comparatively new process in which a rapidly spinning disk is brought into precisely aligned contact with a stationary disk and pressed against it. The heat of friction is so high that the rings of contact melt and the two components fuse.

[More: "GE takes a spin on flywheel electric bus," Electr. Review (England), 28 Sep. 79; Economic and Technical Feasibility Study for Energy Storage Flywheels, ERDA Reprt 76-65/UC 94B (Dec. 75); Proc. of the 1975 Flywheel Technology Symposium 1975, ERDA Repet. 76/85 Nov. 75).]