Cologne, Germany--With auto builders looking for weight savings, higher performance, and more comfort, there has been growing interest in a combined starter/alternator. Conflicting functions, however, have held back integration: the starter being a motor that takes high current and supplies high torque; the alternator a generator supplying a low current for battery charging.
| The Reduced Electronic Device (RED) Pipe houses the ISAD charging circuit and electronic converter. Heat produced by the electronic components is dissipated using an evaporation technique in which a fluid boils at about 30C.
One company working in this field, ISAD Electronic Systems, has fitted an engine with a prototype integrated starter-alternator-damper (ISAD). The design joins a brushless, asynchronous, three-phase motor directly to the crankshaft.
To provide high torque in the motor mode, the ISAD features a special slot shape and a high number of poles. A dc-dc converter first raises voltage to 300V to supply the high current needed for direct crankshaft starting. A 60-mF electrolytic capacitor charged to this level then holds enough extra energy to start the engine. Connecting a static inverter to the capacitor produces the three phases necessary to power the ISAD during starting.
The three voltage phases also enable the machine to run as an induction generator to power the car's electrical systems. In this mode, the direction of power flow is back into the dc system. Under normal running conditions, the induction generator provides an added damping effect by electrically absorbing the torque variations caused as the engine cylinders fire. This eliminates the flywheel in ISAD-equipped engines, decreasing engine weight.
Although the ISAD needs cooling, Klaus-Peter Zeyen, ISAD Electronic Systems technical manager, points out, "If the ISAD is integrated into the engine block during manufacture, then it would be relatively easy to route the water cooling system around the ISAD."
With auto development moving toward more electrical controls such as electric steering, electromagnetic valve drives, and brake-by-wire systems, Zeyen feels that a move to a higher voltage like 36V would give equipment designers more scope and ISAD would not need a starter capacitor at this voltage level. The current needed by these new electrical systems means that belt-driven alternators delivering little more than about 2.5 kW of electrical power may be overtaxed in the future. But with a generated power rating of 6 to 10 kW, ISAD-type systems may prove the solution to this problem.
Additional details…Contact ISAD Electronic Systems GmbH & Co. KG,
Niehler Strasse 102-116, D-50733 Cologne, Germany;
Tel: +49 221 777 3366;
FAX: +49 221 777 3719;
Passenger cars, commercial vehicles, urban transit buses