CVTS GO OFF ROAD

While gaining acceptance in passenger car applications, continuously variable transmission (CVT) systems haven’t made much of a dent in the light truck and SUV market.

While gaining acceptance in passenger car applications, continuously variable transmission (CVT) systems haven’t made much of a dent in the light truck and SUV market. Blame it on the lack of ability to handle low-range mode, which is a requirement for any true off-roader. That’s why eyebrows raised when Jeep announced its 2007 Patriot would be offered in a “Trail-Rated” model complete with a CVT capable of low-range operation. Chrysler execs hope this new advancement will put to rest any concerns Jeep aficionados may have as the brand launches a family of products based on the front-wheel drive C-segment platform—and along with it end the discussion of “sissy Jeeps.” Chrysler’s powertrain engineers began devising the technology to accommodate a low-range mode on the existing Jatco CVT in 2003, when the Patriot began crystallizing through the development process. “We knew right from the start that we wanted the Patriot to be Trail-Rated, so we tasked ourselves with developing a low-range CVT in-house,” says Matt Loddane, chief engineer for the Patriot and its platform-mate Jeep Compass. “The key was to get all the capabilities without a two-speed transfer case.” Chrysler engineers patented the CVT low-range system, dubbed CVT2L.

When the low-range mode is selected via a switch, a controller determines whether the vehicle is traveling at an acceptable rate of speed (the system can only be activated at speeds below 25 mph) and then engages a coupling mechanism, via specially developed software programming, to engage the secondary drive wheel while the CVT moves into a higher final drive ratio of up to 19:1, which is more than enough to traverse just about any dusty trail or rough terrain. Loddane dismisses any concerns over potential durability issues of operating a CVT at such output levels, adding that most of the attention during development was focused on perfecting the calibration and feel of the system. “We had to do a lot of work to make sure the low-range mode would operate like a traditional system from a customer standpoint, so that it would sound and feel familiar,” he says. The CVT2L system will be offered on the Patriot as part of the Freedom Drive II package, which itself is geared for durable off-road use, with 1-in. higher ground clearance, additional body sealing and high-mounted drivetrain vents designed to support 19-in. water fording capability.—KMK