DC-to-DC converter replaces alternator in a hybrid bus

DC-to-DC converter replaces alternator in a hybrid bus

When Allison engineers were designing their H 40/50 Hybrid drive for a bus, they needed low-power electricity (24-V) to power lights, radios, fare boxes, cameras, and other electrical features on the vehicle. So they worked with Vanner, an engineering and manufacturing firm based in Hilliard, Ohio, to design and construct an HBA (hybrid beltless alternator). Like the alternators in conventional cars and trucks, the HBA supplies 24-V power to electrical accessories but is not powered by a belt taking power from a turning motor or shaft. Instead, it converts high-voltage electricity taken from a generator or high-voltage battery pack directly to 24 V power. A built-in voltage regulator ensures the output is 24 V, regardless of engine rpm.

The 75-lb, solid-state device mounts on the bus roof near the battery, a location that eliminates the need for cooling subsystems. Being solid state, the unit is more stable and relatively immune to temperature changes. (High operating temperatures reduce the output of regular alternators.) And unlike traditional alternators, the HBA does not need V-belts, voltage regulators, pulleys, belt tensioners, or hydraulic lines. The HBA even weighs less than normal alternators. These factors make the HBA 25 to 30% more efficient than traditional alternators. This, in turn, means the engine running the bus's generator need not work as hard, so mileage improves and emissions drop. And the unit uses fewer moving parts, so there is less maintenance.

The company is now developing a dc-to-ac converter that will provide power for ac devices, including the air-conditioning compressor, power-steering pump, fans, and water pumps on hybrid vehicles.



Allison Transmission,

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