Power 50 smooth it's liquid - WIP - Hydraulic Launch Assist system from Eaton Hydraulics - Brief Article

Automotive Design & Production, April, 2002 by Christopher A. Sawyer

Imagine a 10,000 lb. truck in fuel-wasting stop-and-go traffic. Now imagine it wasting 25% to 35% less fuel. If the people at Eaton Hydraulics (Eden Prairie, MN) have their way, this will be reality, thanks to the company's Hydraulic Launch Assist (HLA) system. It pumps 600 lb-ft. of torque and 250 hp straight into the driveline, and was previewed on Ford's Mighty F-350 Tonka concept truck.

The unit consists of a reversible hydraulic pump/motor attached to the driveshaft via a clutch in place of the center bearing, and two accumulators. Each accumulator is filled with a combination of hydraulic fluid and nitrogen gas, with high-pressure fluid (5,000 lb/in.) in one, and low-pressure in the other.

Under braking, the fluid flows from the low-pressure accumulator and through the hydraulic pump/motor unit, where it's pressurized and sent to the high-pressure accumulator. During initial acceleration, the high-pressure fluid is released. According to Brad Bohlmann, a member of Eaton Hydraulics Business Development Group, "the pump acts as a motor and provides torque directly to the driveline." This takes about 15 seconds from a full charge, and returns about 80% of the kinetic energy captured by the system during braking.

The HLA unit can drive a 10,000 lb. vehicle to 28 mph without engine assist. In city driving. Eaton expects the device to boost fuel economy by letting the engine idle during initial acceleration. When there is need for greater acceleration, an electronic control unit compensates by adding power from the engine.

"Essentially," says Bohlmann, "the operation of the system is invisible to the driver." This same basic technology is used in hydrostatic transmissions for the off-road market, but hadn't made the leap to on-road applications until electronic controls could smooth out the power flow and decide which unit, or combination of units, will provide the power. One thing it won't have to contend with, however, are the power spikes of a manual transmission. "Most of the vehicles in this class have automatic transmissions with an over-running torque converter," says Bohlmann.

The HLA prototype fitted to the Mighty F-350 Tonka is 78-in. long, and takes the place of one of the side-mounted fuel tanks. "We've worked extensively with Ford," says Bohlmann, "though we can adapt it to other makers' vehicles because the system has quite a bit of flexibility in terms of the angles and positions for mounting." Adding the unit-Eaton expects the 400-lb. unit would be offered as an option-would be a simple bolt-in process. "We expect commercial vehicle owners will compare the cost and economy of a powertrain providing the same power, against the return they'd get from the HLA's higher fuel economy," says Bohlmann. That comparison, however, is several years away.