Jeep Grand Cherokee 2002 | Part Five

Quadra-Drive Four-Wheel Drive System

The Quadra-Drive four-wheel drive system is an industry exclusive on the Jeep Grand Cherokee. It is the first time this innovative system, a combination of the second generation Quadra-Trac II transfer case and Vari-Lok progressive front and rear axle differentials, has been offered on any 4x4 in the world.

The Quadra-Drive system has the ability to keep Grand Cherokee going even if only one front wheel has traction.

"Quadra-Drive is a totally new concept in four-wheel drive systems," said David Van Raaphorst, Executive Engineer – Powertrain, Chrysler Group. "This patented system provides outstanding response and traction under all driving conditions – both on- and off-road – without the driver having to shift any levers or push any buttons.

"It also improves handling stability in wet weather and on slippery roads by making maximum use of available traction during acceleration," said Van Raaphorst.

"This becomes very apparent while cornering and on highway entry and exit ramps. Development of Quadra-Drive, a highly advanced mechanical system, further reinforces our philosophy of using technology where it matters, in this case to reaffirm our four-wheel drive leadership and to strengthen our engineering commitment to Jeep owners."

Under normal driving conditions, the Quadra-Trac II transfer case delivers most of the power to the rear wheels. The moment a wheel loses traction, a speed variation occurs between the front and rear axle causing a gerotor pump to apply hydraulic pressure to a multi-disc clutch-pack sending power to the front axle. This system allows the vehicle to maintain traction and control seamlessly and within a fraction of a second.

As in all Jeep vehicles, the Quadra-Trac II transfer case includes a low range for off-road operation. Selecting low range gives a torque multiplication ratio of 2.72.

Incorporating a speed-sensing torque transfer front differential, Vari-Lok provides a major improvement in wheel traction compared to existing four-wheel drive systems. Under conditions in which opposite wheels are on surfaces with widely different friction characteristics, Vari-Lok delivers far more torque to the wheel on the higher traction surface than is possible with conventional limited-slip systems.

The gerotor pump incorporated in the Vari-Lok differential is conceptually the same as that used in the Quadra-Trac II transfer case. Its operation is virtually transparent to the driver, but the Grand Cherokee"s ability to maintain headway and control under low-traction conditions, both on- and off-road is very evident.

Power transfer in a Vari-Lok differential is proportional to wheel speed difference rather than torque difference as is typical in most mechanical limited-slip systems.

"Four-wheel drive leadership through off-road capability is a hallmark of every Jeep vehicle," said Thomas Hausch, Executive Director – International Sales & Marketing, Chrysler Group. "These new Grand Cherokees retain their unsurpassed off-road capabilities. This has been proven on the Rubicon Trail through the Sierra Nevada Mountains, arguably one of the toughest challenges for any 4x4 vehicle and a prerequisite for all Jeep vehicles."

continues... | Part Six
Published 1 December 2002 Melanie Carter

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