[Don]

Business Week:

ASSISTING THE DIESEL TRUCK ENGINE

"Similar to electric hybrids, hydraulic hybrids draw energy from braking, but are twice as efficient collecting that energy because the braking energy is not wasted by being passed into an electric motor. Instead, this energy is used to power a pump, which transports hydraulic fluid from a low-pressure reservoir to a high-pressure accumulator. As more fluid passes into the accumulator, the pressure grows, eventually being released as energy that is used to directly power the vehicle's driveshaft. "

" This allows the vehicle to move from a stop without taxing the diesel engine, which typically performs poorly while accelerating. Diesel engines are most effective when running at a steady rate, and lose a tremendous amount of efficiency when accelerating; the hydraulic system compensates for this weakness, and lets the diesel engine do its work once it's up to speed. This is especially important for UPS trucks that stop 60 to 70 times per day for deliveries and operate mainly in stop-and-go city traffic, where the hydraulic system can carry most of the burden. "


http://www.businessweek.com/print/bw...116_037066.htm