The Silverado is called a Two-Mode Hybrid because in Mode 1 the first electric motor, which also replaces the torque converter, silently drives the truck off the batteries up to 32-mph, and as far as one to two-miles, depending on charge levels. The transmission can also simultaneously balance gearing and input from the gas and electric motors at low speeds like a traditional single-mode or 'parallel' hybrid to drive the truck's wheels.
Mode 2 kicks in above 32-mph, when both electric motors supplement the V8.
Proper gearing is critical to enable the Silverado Hybrid to operate at peak efficiency at all times. There are two sets of gears for the dynamos to leverage at low (Mode 1) and high (Mode 2) speeds and a third set of four fixed gears just for the V8.
In Mode 1 the first motor uses the first gear set. Both electric motors shift to the second, higher set of gears at cruising speeds when they help the gas engine stay in V4 mode longer to save fuel.
If the truck is pulling a load, the transmission locks out the electrically variable gears and both electric motors. It shifts over to the four fixed gears, so the V8 is the only engine powering the truck. In this 'third' mode the pickup operates just like a conventional 6.0-liter V8 and can tow up to 6,100-pounds in the two-wheel-drive version.
The Two-Mode Hybrid uses a 42-volt power steering system to gain up to an extra .5-mpg compared to conventional hydraulic power steering systems. A hydraulic steering pump always requires power, even when the truck is traveling in a straight line, while the electromechanical steering system only requires power during turns. The 42-volt steering system will eventually make its way into all of GM's pickups, not just the Two-Mode.
GM says it expects somewhere between 5% to 10% of all 2009 Silverado pickup sales will be the new hybrid model.
Larger Chevy dealers are expected to keep a demo unit on their lot to let potential buyers take a test drive but shoppers will likely have to special order a Hybrid Silverado instead of taking one home the same day they drive the demo. A limited set of options and configurations (e.g. 2WD or 4WD) will ensure that truck can be delivered rapidly after an order is placed.
Final pricing hasn't been announced yet, but like the Chevrolet Tahoe and GMC Yukon SUV Two-Mode Hybrids that carry a price premium over conventional counterparts, the Silverado will almost certainly carry a higher price tag than a similarly configured conventional pickup. Part of that premium is expected to be recovered with tax breaks from the federal government for buying a hybrid. There's $2,600 cash back for the Tahoe and Yukon Hybrids. No word yet on the cash back amount for the Silverado.
We'll have more information on this truck during our LA Auto Show coverage in Los Angeles. If you'd like to know more technical aspects about the Two-Mode system, also check out our GM Hybrid Tech Preview story.
GM's Press Release is on the next page.