by Dan Carney
On sale: 2003?
Estimated pricing: $30,000
"The power of a V8, with the fuel economy of a V6." We've heard the claim repeatedly over the years applied to various technologies such as turbocharging and cylinder cutout systems such as Cadillac's ill-fated V-8-6-4. For the most part, these claims have not been met in real life.
DaimlerChrysler is, however, developing a system that really does deliver better than V8 performance in a V6-powered Dodge Durango sport-utility. The company demonstrated such a vehicle to us in a series of drag races: the 175-horsepower 3.9-liter V6 Durango vaulted off the line and left the 250-horsepower 5.9 liter V8-powered version. This is because it got a significant boost from a 73-horsepower electric motor. Gas mileage is also up: The hybrid V6 gets 18.6 miles per gallon, compared with the V8's 15.5 mpg, a 20-percent improvement.
The technology that makes this possible is unexpectedly simple. DaimlerChrysler calls the Durango a "through the road" hybrid, because the gasoline and electric motors are not connected to each other. Instead, they each drive a different pair of wheels, with the power combined "through the road" or TTR, as DaimlerChrysler calls it.
The Durango makes an ideal candidate for a TTR hybrid drivetrain for two reasons. It is a four-wheel-drive vehicle, so customers already expect it to put power through all four wheels. Also, as a large SUV, it gets pretty poor gas mileage. A 20-percent improvement in efficiency for a gas-guzzler saves a lot more fuel than a similar improvement in an already-efficient small car, so the technology is more beneficial.
The hybrid Durango is a normal V6-powered model, driving the rear wheels only. Engineers installed an electric motor/generator connected to the front wheels. When maximum power is needed, both engines push the Durango with their full might. Under braking, the electric motor becomes a generator (an alternator, actually), recharging the battery pack so it has energy for acceleration. If the battery gets too low, the generator will engage while driving, but most of the energy for charging is supposed to be recovered from braking.
Driving the hybrid Durango is amazingly normal. The truck has the same ride and handling characteristics as every other Durango, but it has more urgent acceleration. The electric drivetrain emits a whine under full-bore acceleration that is somewhat reminiscent of a supercharger.
It is little surprise that more power makes the Durango fun to drive, but what is surprising is how well the regenerative braking system is integrated with the hydraulic brakes. The prototype has a display on the dash indicating the battery's state of charge and how much power is going to or coming from the electric motor. Lightly feathering the brake pedal to just engage the generator produced no unnatural sensations. It is impossible to tell where the electric braking leaves off and where the hydraulic braking starts.
Calibrating the power controller for the electric motor was a challenge, according to Thomas Moore, vice president of DaimlerChrysler's Liberty technical center. But coordinating the gas engine's throttle with the electric motor turned out to be simpler than expected, he said. "The gas engine notices that its load has been reduced when the electric motor assists, but it just goes faster when that happens," he said. "It doesn't seem to care why the load got easier, it just thinks it is going down a hill or something."
When the Durango goes down a real hill, the system recovers energy when coasting, not just when braking. Lifting off the throttle doesn't cause the Durango to whir to a halt, however. At highway speeds, the effect of the generator is virtually undetectable. At lower speeds, with less inertia, the effect becomes more apparent. Coasting below 15 miles per hour feels like the driver is lightly dragging the brakes for a smooth stop. In traffic, drivers may not need to touch the brake pedal.
We didn't get to drive the hybrid Durango off-road. DaimlerChrysler says the hybrid drivetrain is not meant for serious off-road use or for heavy-duty towing. But it does provide the all-wheel drive, all-weather security blanket that attracts so many buyers to SUVs.
Of course, all the magic doesn't come without a price. The test Durango weighs about 250 pounds more than the gasoline version. But the company expects that a production version of the hybrid would weigh the same as the gas truck, thanks to removal of the transfer case and front differential as well as weight savings in components that can be made lighter for the lower-powered V6 engine.
But even in production, the hybrid will cost about $3,000 more than a conventional Durango. So the company is urging Congress to pass a bill that would give buyers a tax credit for buying hybrid vehicles. For the Durango, that credit would be $3,000, so customers can be environmentally responsible without lightening their wallets. If this happens, DaimlerChrysler thinks it can sell 50,000 to 100,000 hybrid vehicles a year. The drivetrain would be applicable to Dodge trucks and to Jeep vehicles too, so hybrids could appear in a variety of vehicles.
Even so, a hybrid Durango won't be in showrooms before the 2003 model year, while a lithium ion battery is developed to replace the old-fashioned lead-acid battery in the prototype.
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