Sorting out the CVT: Interview with Chrysler's Ronald Kruger

August 15, 2007 by Justin Pritchard , Auto123.com
I get plenty of reader e-mail asking questions about the new breed of Continually Variable Transmissions starting to make their way mainstream. To help answer the more common questions, I recently interviewed Ronald Kruger, the Supervisor of CVT engineering at Chrysler. He explained where the CVT came from, what its limitations are, how people like it, and where it's going. JP Where did the CVT come from? Was it always used in cars, or adapted from another type of vehicle? RK As in most new powertrain technologies the CVT was derived from a need for improved fuel economy. Continuously Variable Transmissions have been around in automobiles for a very long time, but now they are becoming more popular because of advancements in metal belt & chain technologies and electronic controls. JP In a nutshell, how does it work? 2007 Dodge Caliber RK There are no shifting gears in a CVT (except the reverse gear). The transfer of power & torque from the engine to the wheels is through a metal belt or chain that runs between two pulleys that each have opposing conical belt surfaces (cones). The pulley cones can move together or apart by hydraulic pressure, depending on the programming. Thus, the CVT will change ratio smoothly as required to accelerate an automobile without the driver or passengers noticing. JP Why not just use a regular automatic transmission? RK CVT's can continually allow the engine to operate at optimal fuel efficiency points, where step ratio (gear) type automatic transmissions can only operate at these points momentarily. CVT's can also allow the engine to hold at its maximum power point during acceleration, where step ratio automatic transmissions can only operate at these points momentarily too. CVT's have replaced step ratio automatic transmissions and achieved fuel efficiency increases of 5% to 15% in automobiles. JP Are there certain applications where a CVT is a better fit than in others? RK The CVT would work well in many applications but mostly in medium to light-weight vehicles. The Dodge Caliber, Jeep Patriot and Jeep Compass owe part of their impressive fuel economy to the CVT technology. JP Are there any limitations to a CVT? Can it do anything an automatic can't?