Ford Motor Co. announced June 20 it is developing an innovative Hydraulic Power Assist (HPA) technology that may help large trucks be up to one-third more fuel efficient in stop-and-go driving than they currently are.Ford demonstrated the HPA system on a Lincoln Navigator at FutureTruck '02. According to the company, the Ford HPA system will reduce fuel consumption while increasing vehicle performance. A reversible hydraulic motor and an energy-storage accumulator recover energy normally lost during braking - storing it as hydraulic pressure to be later released to provide a boost for acceleration. Launching a heavy vehicle from a stop requires much more energy than keeping that vehicle in motion. Adding a hydraulic boost allows the vehicle to accelerate much more quickly than the same truck without it, while greatly decreasing fuel consumption and exhaust emissions. Ford first showcased HPA in a concept truck, the Mighty F350 Tonka, at the North American International Auto Show in January. Ford research indicates that the installation of a HPA system on a medium-duty truck could in-crease fuel efficiency in stop-and-go driving by 30 to 35 percent and cut exhaust emissions by at least 20 percent. Ford says HPA could be used in commercial trucks and vans operating in stop-and-go duty cycles — such as delivery trucks and airport shuttle vans. These fleet vehicles would be ideal because their drive cycles would result in a rapid payback in operator fuel savings. According to Ford, the installation of HPA could allow for smaller, more fuel-efficient engines in commercial vehicles - since less engine horsepower and torque would be required to move the vehicle from a stop or in hill-climbing. The Lincoln Navigator research vehicle with HPA features a 4.0-liter V8 Jaguar engine developing 290 hp at 6,100 rpm and a peak of 290 lbs.-ft. of torque at 4,250 rpm. Designed for the 4,000-lb. Jaguar XJR, the engine needs the torque boost from HPA at low engine speeds to competitively accelerate the 6,000-lb. Navigator from a stop. The Ford HPA system demonstrated on this research vehicle provides up to 600 lbs.-ft of torque up to 2,000 rpm (drive shaft speed). Navigator's standard engine is a 5.4-liter 32-valve V8 that develops 300 hp at 5,000 rpm and a peak of 355 lbs.-ft. of torque at 2,750 rpm.