Lexus Engineer Details the Twin-Transmission Setup of new LC500h
Lexus’s latest hybrid model, the LC500h, features a unique transmission setup. It has a four-speed gearbox connected to the CVT. The technical solution takes away the “rubber band” feeling of CVTs, and here’s how it works.
The twin-transmission setup was detailed by Koji Sato, chief engineer for the Lexus LC500h project. In an interview with Automotive News at this year’s Geneva Motor Show, the engineer in charge of this project explained how and why the Japanese brand chose to link two transmissions together to provide an exciting driving experience.
The idea behind this technical solution was to eliminate the “rubber band feeling” that comes with all conventional CVTs. If you are unfamiliar with the phenomenon, it goes like this: you press the gas pedal hard, the revs go up and they stay there while the car accelerates.
On a regular car, you might think that your clutch is slipping, or that there’s something seriously wrong with the automatic transmission, but that is how CVTs respond to hard acceleration.
Lexus wants to change this and stop it from happening to their new cars fitted with a multi-stage hybrid system. The solution was not to introduce a twin-clutch gearbox or an eight-speed automatic, but to keep using the CVT transmission with a four-speed automatic gearbox.
The idea behind the mating of the two gearboxes is that the four-speed automatic modulates the CVT’s output and creates an intentionally perceived gearshift. The pair of gearboxes simulates the shifting of six gears in total, but the trick is that the driver will not be able to tell if the car shifted a gear through the automatic gearbox or the CVT did the work. It is improper to say that the CVT transmission shifts, as these units continuously change their ratios instead of actual gears.
The new Lexus LC500h is the first model in a long line to use the new transmission, as the Japanese brand plans to use the system in several other cars. The first potential recipient of the new twin-tranny system is the next LS, expected to go on sale next year. Other Lexus models with longitudinally mounted engines could also get this hybrid system.
We believe Lexus chose this solution to be able to mate the electric engine of the LC500h with its naturally aspirated 3.5-liter V6 unit.