Answering the demand for machines that use less fuel and run cleaner, two leading construction-equipment manufacturers wowed crowds with innovative propulsion systems at last month’s Conexpo show in Las Vegas.
Hybrid Wheel Loader
Volvo Construction Equipment, Asheville, N.C. (volvo.com), unveiled a preproduction prototype of its L220F Hybrid wheel loader. Company officials say it offers more power, better performance, and a 10% reduction in fuel consumption, compared with current versions.
The heart of the parallel-hybrid system is an electric motor called an Integrated Starter Generator (ISG). Fitted between the engine and transmission, the ISG is coupled with a lithium-ion battery with a several hundred watt capacity.
The ISG works in a number of ways, explains Arvid Rinaldo, manager of global markets. “In many applications, up to 40% of a wheel loader’s time is spent idling.” When stationary, the hybrid system automatically shuts down the engine but still runs electronic and climate-control systems for up to an hour. And as soon as the operator hits the throttle, the ISG restarts the engine.
The ISG also overcomes the problem of low torque at low engine speeds inherent in diesel engines. “Traditionally, you have to rev up the engine to get more torque,” says Rinaldo. “But the electric motor is just the opposite; from 0 rpm we get high torque. At start-up we boost the diesel engine with the electric motor, which gives us much faster machine response at lower revs. The operator gets more power, so it’s easier to drive as well.” The ISG’s electric motor generates up to 516 lb-ft of torque from standstill. Put in engine power terms, it adds up to 67 hp of mechanical energy.
The combination of these two attributes means the diesel engine can remain off for long periods when it would otherwise be idling and the operator doesn’t need to over-rev the engine to get sufficient working torque. The battery recharges when full engine output is not needed, with the ISG acting as an alternator.
Other energy-saving innovations on the L220F Hybrid include a switch from belt-driven to electrically powered a/c compressor and fan. The same goes for the ISG replacing the starter motor and generator. “Eliminating belt-driven accessories saves a lot of power,” adds Rinaldo. The next-generation version, set for delivery in 2009, will also feature regenerative braking.