An Idle threat

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Layout and operational modes of GM’s new Flex Power system.

Chevrolet and GMC will introduce the first of GM’s new hybrid vehicles as Flex Power models in their 2004-model Chevrolet Silverado Fleetside and GMC Sierra Wideside lineups. The new Flex Power models are said to provide significant improvements in fuel economy and emissions, and they offer accessory AC power through two 110-volt outlets – a major bonus for contractors and campers.

A key contributor to the Flex Power’s fuel efficiency, says GM, is its ability to automatically stop the engine when the vehicle stops, and nearly instantaneously restart it when the driver releases the brake or presses the accelerator pedal. Little or no idling.
GM’s goal was to make the system transparent to the operator and, after a short drive around Pontiac, Mich., I’d have to say they’ve succeeded.

Instead of a conventional starter motor and alternator, Flex Power pickups use a compact 14-kw electric starter/generator nestled between the engine and transmission. It provides fast, quiet starting, and generates electrical current to charge the batteries and provide AC voltage. It also provides coast-down regenerative braking.

The starter/generator includes a rotor and stator, housed inside the transmission bell housing. The stator is attached to the engine block and incorporates smaller sized coils formed by laser welding copper bars together instead of winding with copper wire. The rotor bolts directly to the engine crankshaft and spins inside the stator. Current flowing through the stator’s electric windings generates magnetic forces in the rotor, which causes the rotor to turn, starting the engine. The starter/generator is in series with the engine, so that when the engine is turning, it is turning and vice versa.

The new pickups use GM’s Vortec 5.3-liter V-8 and Hydra-Matic 4L60-E four-speed automatic transmission, but a host of electronic control modules are used to control powertrain functions.

For example, a starter/generator control module (SGCM) controls the flow of torque/energy into and out of the starter generator. The SGCM controls the starter generator’s engine cranking, torque control, speed control and torque smoothing/active damping functions. It also controls the accessory power module, which generates four types of power: 14-volt DC, 42-volt DC, 120-volt AC and 28-volt AC for the starter function.

Three lead-acid batteries provide power for the 42-volt system. The deep-cycle cells employ absorbent glass mat technology, specifically designed for hybrid vehicles, and are tailored to GM performance requirements.

Steering assist is provided by an electro-hydraulic power steering system, which works even when the engine shuts down, and the HVAC system has extra large capacity to provide warm or cool air when the engine is off. If needed, the engine will restart to keep the cabin comfortable.

And there are safety features. Because higher voltage poses an increased risk of fire during a collision, a pyrotechnic device disconnects the batteries when an air-bag-deploy signal is sent. Also, the engine will maintain its mode, running or stopped, when the hood is opened. You definitely don’t want any surprises when you’re checking your oil.

The Flex Power system, combined with an early-lockup torque converter and a fuel cutoff that kicks in at speeds below 13 mph when the driver lifts off the accelerator, should enable the new pickups to achieve a 10- to 15-percent increase in fuel economy, says GM.