General Motor’s has officially announced that it will begin mass production of hybrid versions of it’s popular large SUV vehicles the GMC Yukon and Chevrolet Tahoe. The cars will be available for purchase in the 4th quarter of this year.
GM-Volt.com moderator was given the opportunity to test drive one of the pre-production models right in the crazy yellow-cab filled traffic of NYC, and to discuss the cars with Vehicle Chief, Full Size Truck Hybrid Mark Cieslak and Assistant Chief Engineer Small block truck engines Chris Meagher.
These vehicles are unique for two reasons, they are the first-ever passenger vehicles to have a 2-mode hybrid system, and they are the first ever large SUV hybrid vehicles on the planet. While they aren’t Volts, they are a step in the right direction.
Standard hybrids like the Toyota Prius use a single mode hybrid system, meaning the electric motor powers the car only at low velocities, once speed or acceleration increases, the car goes to all combustion. In the 2-mode Yukon and Tahoe, there are two separate electric motors directly linked into the transmission. One powers the car at low velocities, whereas the other one kicks in at certain high speed conditions. This allows the vehicles to improve fuel economy both in city and highway driving. Indeed the car gets a 40% improvement in fuel economy in city driving, and overall a 25% improvement over the non-hybrid base models. Further gains in fuel economy come from the truck’s abilities to shut off 4 of the 8 cylinders, and to use a variable displacement oil pump.
The cars are engineering marvels and contain the most sophisticated on-board computer and software systems on the road. In order to achieve the best possible fuel economy, the computer analyzes the car’s driving state 50 times per second and determines which configuration; electric motor 1, electric motor 2, four or eight cylinders, or ICE shut-off will be most energy-efficient.
Some modifications of the vehicles structural components had to take place to make up for the increased weight from the hybrid system and batteries. This included an aluminum hood and improved aerodynamics of the front grill and running boards. The car uses a 300V NiMh battery housed under one of the rear seats, and has a 6.0 L engine.
Getting into the driver’s seat (I drove the GMC Yukon), it feels like any other large SUV. Differences become apparent when one looks at the dash. There is an indicator showing the driver’s role in the trucks ecomony. If you accelerate too hard the needle goes to the right (burning too much fuel), if you brake too hard it goes to the left (losing stored energy by activating non-regenerative brakes). If your driving is optimal, the needle stays in the green zone.

Starting the car comes straight from the electric motor, and you do not hear the whine of the starter. When stepping on the accelerator, one feels the unique instant responsiveness of the electric motor. While driving one can barely perceive when the gas motor switches on and off, and indicator lights show if the ICE is on or off, in 4 or 8 cylinder mode, and which electric motor is running. On the in-dash nav screen all of this data is displayed graphically.
Overall, a very responsive, agile and well-handling ride, and a lot of fun.
One might ask if it isn’t paradoxical to have a giant gas-guzzler as a hybrid, but Mark’s answer is that it is actually a “perfect marriage”. Since this type of vehicle is generally so fuel consumptive, making hybrid gains on it are very valuable. Plus one can do all the heavy hauling needed, while still reducing oil consumption. The non-hybrid version of these trucks get 14 mpg city/19 mpg highway. With the 2-mode hybrid system, those numbers go to 20 mpg city/? highway (not federally approved yet).
When asked what he’s most proud of in these vehicles, Marks reply is “best technology, best efficiency, and best capability of any hybrid vehicle on the road today”.
While they’re not Volts these machines bring us closer to that goal. Indeed, these are two of several hybrids GM is putting out this year. And expect to see the 2-mode systems in upcoming Escalades, Saturn VUEs, and pick-up trucks.
Pricing is not finalized yet, but will fall within the same price range of the current Tahoe and Yukon lineups.
