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Parallel Hybrid Powertrain

Ever use your pickup truck to watch television, microwave popcorn and light up your house at the same time? Well, if you live in California these days you probably wish you could and you will be able to by 2004 when GMC starts shipping Sierras with its new Parallel Hybrid Powertrain, aka Flex-Power.

GMC has taken a different approach to the hybrid vehicle philosophy and designed the electric drivetrain components as supplements to the normal displacement motor, not replacements for some portion of the gas generated power.

Compared to the hybrid powertrains found in Toyota's Prius and Honda's Insight, the electric motor in the Sierra doesn't power the vehicle at low speeds but is used to restart the gasoline engine, which shuts off at stoplights instead of idling. This means no compromise in power or towing, clear advantages in emissions and a claimed 15% bump in gas mileage. Plus the ability to use the truck as a generator and source of stored power.

Like the Displacement on Demand truck, the PHT Sierra shows no exterior differences from a regular Sierra.

GMC engineers have inserted a 42-volt motor into the 285 horsepower Vortec 5300 engine, between the crankshaft and transmission, eliminating the need for a starter and alternator. The benefit of this motor is its ability to also power household and work-related appliances.

Today's conventional vehicles use 12-volt power systems, so more volts means redesigning everything from light bulbs to major systems. The power steering motor, for instance, in the Flex-Power concept we drove, used a 42-volt replacement part, smaller than the original equipment, and capable of operating with the engine off. But most truck components won't be redesigned to take advantage of the 42-volt capabilities until well after 2004, likely requiring production PHT Sierras to come equipped with dual voltage systems to power both 42-volt and traditional 12-volt components.

As far as driving the PHT Sierra, well, it takes a little getting used to. It's kind of like driving using a manual transmission and forgetting to put the vehicle in neutral or releasing the clutch while still in gear at a stoplight. The engine just 'stalls' but in the PHT Sierra you still have full air conditioning, full steering abilities and radio. It's only when we lifted our foot off the brake that the engine seamlessly restarted to move us on our way.

The electric motor includes a brain that determines loads, and when to engage the gas motor for drive and for recharging. If there is too much load on the truck, say when the AC is blowing full tilt, the gasoline engine may not shut off when stopped. The electric motor is also purposed with torque smoothing for shifts and engine engagement, but with the test mules we had, the shift points and torque smoothing was clearly something GMC was still working to perfect.

A 42-volt electric motor replaces both the starter and alternator and stores power in lead acid batteries under the rear passenger seats. Electric outlets are accessible within the cab and bed.

At the halfway point in our test drive we were given a convincing demonstration of the PHT's power generating capabilities. We pulled the Sierra up to a tent and plugged the truck in to watch television, turn on a set of reading lights and microwave some popcorn. GMC claims that the Flex-Power truck provides 4.8 kW of electricity. That's enough to keep a small house running.

Three large lead-acid batteries are positioned under the rear seat to store power, mostly occupying space that wasn't very usable to begin with anyway. An outlet is also provided under the seat so that a laptop computer or other device can be powered inside the car using the electric assist.

The PHT Sierra also uses regenerative braking to capture energy and recharge the battery packs while slowing the truck.

Displacement on Demand uses the oil pump system for hydraulic pressure to activate the system. Four control valve solenoids then act together to achieve seamless transition between four and eight cylinder operation.

One popular question asked by all the journalists was about the convergence of DOD with Flex-Power, and wouldn't that make the right mixture of fuel saving technologies for a top-selling vehicle with substantial influence on the company's CAFÉ metrics. Low-end power needs would be met by the electric-gasoline hybrid engine during stop and go traffic and high-end power needs would be met by the DOD engine during light-duty driving. The engineers and others present seemed to agree that this would be the right blend of features for some of the thirstiest vehicles on the road.

Although the new trucks were clearly a highlight of the event, the overall impression of "Professional Grade" came, first and foremost, from the GMC engineering team, and their complete involvement with, and obvious passion for, the development of first-rate products. Talking to Gene Rodden about Quadrasteer and suspension engineering to account for towing requirements was a real plus. Chris Meagher, the Yukon Denali racer in GMC's commercials, was consistently available for questions and very solicitous of detailed responses from the journalists. Mark Cieslak, also star of GMC stage and screen, was a great listener and constantly took notes on ideas offered by drivers and reviewers of the vehicles. We came away as impressed with the people behind the trucks as the trucks themselves.

We really enjoyed and think highly of the concept vehicle-type technology we had a chance to drive. With 2004 rapidly approaching, a new Sierra with all-wheel drive, Quadrasteer, Flex power, and DOD would be the real benchmark in the industry for fuel efficient light trucks.

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