When Oscar Jackson retired in 2003, having licensed his legendary Jackson Racing tuning company that specialized in supercharging Hondas and Miatas for 15 very successful years to Moss Motors, his plan was to kick back and enjoy the good life in Colorado with his family. Then, while on a trip to Europe, including a visit to the Isle of Man for its famous TT race, he came across a new technology that lured him out of retirement. That technology is the Rotrex traction drive supercharger, and in Oscar’s own words, “This is the tool I’ve been waiting for my whole life. With the Rotrex, all of the deficiencies I’ve experienced with turbochargers and superchargers over the last 30-plus years in the business were suddenly and very elegantly addressed.”
The technological starting point for Rotrex superchargers dates back to the early ’70s, when Anders Kolstrup, the company’s current technical director, began looking for improvements in engine development and performance as part of his hobby as a racer. Many years later, in 1996, the first Rotrex-related patent was issued and in 2000 the Copenhagen, Denmark-based company was established. But what’s so special about Rotrex and its patented traction drive technology that it pulled a supercharging legend like Oscar Jackson out of retirement, attracted Ferrari super-tuner Novitec Rosso and found its way onto the world’s fastest car, the 1,018hp Koenigsegg CCXR?
Visually, Rotrex superchargers look a lot like conventional centrifugal superchargers, both of which use a compressor side similar to that of a turbocharger (a compressor housing and impeller that connects to the main shaft). Rotrex superchargers are beltdriven, just like a standard centrifugal blower, so boost pressure increases with engine speed (since the pulley on the supercharger is spun by the main accessory belt that is powered by the crankshaft pulley). However, unlike conventional geardriven centrifugal superchargers that build comparatively little boost at low engine speeds because they have insufficient impeller speed (up to a maximum of about 70,000 rpm), Rotrex’s patented traction drive system can achieve impeller speeds up to 250,000 rpm, allowing the use of a smaller compressor wheel (sized more like a turbocharger compressor wheel) that operates within its optimum efficiency range more quickly and consistently.
The cutaway image of a C30 Rotrex supercharger shows you some of its inner workings, inclu
But how are higher shaft speeds, greater efficiency and smaller packaging possible? It is the “planetary drive” with its patented “ramp effect” that make the Rotrex so special. These three planetary rollers are fixed in place 120 degrees from each other. They are enclosed within an annulus or “drum” that is turned by the input shaft via the serpentine drivebelt.
According to Oscar, “If you consider that the annulus/drum, planets and compressor shaft are all just smooth steel parts spinning on themselves without gears, it makes sense that at some point when there is a high load from the compressor making boost that these parts are going to slip on each other [causing inconsistent torque delivery]. But the ramp effect keeps this from happening. One of the planets is actually allowed to move slightly from its fixed bearing position. As the annulus/drum rotates, it exerts load onto the planets such that one planet is allowed to rotate slightly loose from its normal position. This loose planet then exerts a downward load onto the compressor shaft and the compressor shaft then loads up against the other two planets, preventing slip and keeping the torque consistent from low-load to high-load conditions.”