While it seems strange to call any hybrid drive setup “traditional,” there is a growing familiarity with the parallel type, which can use electricity and/or internal-combustion power to propel a vehicle. This is done by means of an electric motor sandwiched between the engine and transmission, with either the engine or electric motor feeding power to the transmission input shaft, depending on power requirements.
The systems also employ regenerative braking, which means that, during deceleration, the electric motor is driven by the wheels and becomes a generator for recharging the batteries, while slowing the vehicle. The Toyota Prius, for example, has used such a system for a few years now, and Eaton is offering its beefier version for medium-duty trucks.
Now, we’ve learned, General Motors’ Vortec V-8-powered Chevrolet Tahoe and GMC Yukon, with GM’s two-mode hybrid drive systems – similar to those described above – will go on sale this year as 2008 models, but pricing and production volumes have not been announced yet.
The two-mode system is expected to deliver a 25 percent improvement in composite fuel economy when paired with the company’s Active Fuel Management system, which selectively deactivates cylinders not needed for driving conditions at hand.
The two-mode system works like this: In the first mode, at low speed and light load, the vehicle can operate on electric power only, engine power only, or any combination of both. When operating with electric power only, it reportedly provides maximum fuel savings by leaving the internal-combustion engine shut off for extended periods of time, such as in heavy stop-and-go traffic.
While two-mode can be adapted to many different types of vehicles, including those in commercial applications, it won’t come cheap, at least initially, in that major drivetrain revisions, with attendant packaging considerations, are needed. However, the GM Hybrid system, although something of a “hybrid light,” promises easier adaptation to vehicles, since drivetrain changes aren’t needed. While the Saturn Vue admittedly isn’t a vehicle with commercial aspirations, it has been a showcase for the system, whose beauty is in its simplicity.
The Vue Green Line uses electronic controls and a multifunctional electric motor/starter/generator – which is mounted in place of the standard alternator – on a 2.4-liter, variable-valve-timing, four-cylinder engine, mated to a 4T45-E four-speed automatic transmission. The system increases fuel economy through engine shut-off instead of idling, fuel cut-off during deceleration, the supply of electric power assist during acceleration (up to 18 mph), and the ability to capture electrical energy through regenerative braking.
