Schwieberdigen, Germany--With the growing number of electrical loads in modern vehicles, alternator designers have had a hard time keeping up. Average ratings have doubled from 35 to 70A in the past two decades, and 90A models will soon be common.
| Liquid-cooled design with static field coil eliminates wear-prone brushes and slip rings.
At higher outputs, a fan-cooled alternator must work much harder to compensate for increased power losses and higher temperatures, which are more difficult to dissipate in today's increasingly cramped engine compartments. A bigger fan might once have been acceptable, but now there is a demand to reduce fuel consumption as well as noise generated by ancillary equipment in the engine bay. Added to this is the threat of tough new European legislation to restrict the "pass by" noise generated by moving vehicles to 74 dBA.
Engineers at Robert Bosch GmbH believe they have solved these issues with a new liquid-cooled alternator that is 8 dBA quieter than its air-cooled equivalent. Instead of a fan, coolant from the engine's cooling system passes through a water jacket in the alternator casing to keep the body and its sensitive electronics from heating up.
Because the field coil is fixed around the rotor shaft, the Bosch liquid-cooled alternator needs no slip rings or brushes. The pole wheel rotates between the static field coil and the stator winding in the alternator housing. The magnetic field thus traverses two air gaps instead of one in a traditional design. By eliminating rotating electrical parts, Bosch predicts service intervals can be extended to 200,000 km for the new alternator.
Large vehicles with direct-injection, turbo-charged diesel engines comprise the alternator's initial market. Modern turbo-diesels are highly efficient, but their low heat loss has its drawbacks for vehicle occupants on a cold morning when it takes so long to warm up. Supplementary electrical heating counters the morning chill, but puts a heavy load on the alternator, pushing current demand above 150A.
The water-cooled alternator can meet these high demands and, as a bonus, feed warm water into the cooling system and thereby warm the vehicle more quickly. Water leaving the alternator jacket is 3 to 5C warmer than the water entering.
Additional details…Contact Klaus Kasten, Robert Bosch GmbH, Robert Bosch Strasse 2, 71701 Schwieberdigen, Germany; Tel: +39 711 811 8090; e-mail: Klaus.firstname.lastname@example.org ; or Circle 502.