Still, an accumulator tank with enough volume to launch a heavy truck up to speed is relatively bulky. The Tonka concept's two tanks, housed between the frame rails, are each slightly less than a foot in diameter and about 2 feet long. They're reinforced with carbon fiber to withstand pressures that can reach 5,000 psi, and lined with a material that absorbs the heat generated when the gas compresses. The pressure in such tanks is high, so safety testing has been thorough -- similar to what storage tanks for compressed natural gas receive. The hydraulic motor itself, mounted midships alongside the tank, is compact, roughly the size of a standard differential.
With the tank charged, the system nearly duplicates the power of the primary diesel, adding another 600 lb.-ft. of torque to launch the truck from a standing stop. This is enough to let it drag race competitively with a BMW roadster, and also means that the engine doesn't need to kick in until the vehicle is rolling at 20 to 30 mph, when it is operating at a more efficient rpm range. Brake life also benefits -- with the system providing most of the stopping force, brake linings last three to five times as long.
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.