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12 November 2008
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Dual-speed drives boost alternator efficiency
Transmission specialist Antonov Automotive has claimed that simple dual-speed drives can help alternators and other engine ancillaries operate more efficiently, by better matching their drive speed to the vehicle requirements, and improve the re-charging of batteries.
The characteristics of Antonov’s mechanical module (AMM), essentially a self-controlling automatic two-speed gearset, can be tuned to meet specific vehicle requirements. For example, mated to an alternator it provides improved alternator matching to give good charge at engine idle without incurring losses at higher engine speeds.
In this application, it can also provide a reduction drive to enable a compact front-mounted starter-alternator to be used for engine stop-start operation.
The company, which is developing the system for OEM applications, says a dual-speed alternator designed for stop-start operation can deliver an 18% saving of electrical energy over a typical light commercial vehicle duty cycle.
It can also be applied as a dual-pulley unit to give a two-speed belt-driven alternator, air-conditioning pump and water pump, whereby the accumulated energy saving translates into a 5.6% reduction in fuel consumption. This is achieved with a 2-to-1 gear ratio change at 2,000rpm.
Ultimately, the company aims to introduce a compact unit mounted directly to the engine crankshaft, but this will require much greater development integration with the base engine.
“Customers and legislators are placing more demands on vehicle electrical power, with lower emissions meaning smaller petrol and diesel engines, lower engine idle speeds and more stop-start systems,” says Chris Baylis, operations director at Antonov. “Even daytime headlight legislation is increasing the electrical load.”
The introduction by carmakers of belt-driven stop-start systems and other developments, such as downsized engines, is increasing the need for more efficient electrical systems.
Vehicle manufacturers also want more engine torque at low engine speeds to improve drivability as well as bring better fuel efficiency.
“Maximising the overall operating efficiency with fixed drive alternators, water pumps, superchargers – indeed any crankshaft driven or electric motor ancillary – is becoming more and more difficult,” says Baylis. “At high engine speeds this can result in unacceptable losses or even excessive speeding outside their most efficient operating range.”
Applied to an alternator, the Antonov dual-speed module can increase the electrical output for regenerative braking and reduce engine idle speed without battery charging issues. A smaller dual-speed alternator can match the low engine speed output of a larger, more expensive alternator, and there is also reduced noise at higher engine speeds.
Another use for Antonov’s AMM device is to facilitate low-cost engine downsizing: it can be used as a two-speed drive with a centrifugal supercharger. The higher drive ratio at low engine speeds provides what Antonov claims is a big engine feel from a small engine, allowing for less gear down changing and improved fuel economy.
© PE Publishing, 12 November 2008
