Prime Cuts: Lexus Variable Gear Ratio Steering

We slice open the activist of active systems.

FEBRUARY 2012 BY TONY QUIROGA

The ability to change a vehicle’s steering ratio has many advantages. A quicker ratio (fewer turns lock-to-lock) can give a vehicle a deft feel. At high speeds, switching to a slower ratio (more turns lock-to-lock) imparts a better sense of stability. Lexus is not alone in using a computer-controlled system to change ratios, but its approach is pretty trick. Note that this type of active steering is far more involved than the variable-ratio units with rack teeth cut at differing angles; they can’t make ratio changes on the fly over the full range of lock. The more complex Lexus (and Audi) approach is essentially a gearbox built into the steering column between the steering wheel and the pinion gear. Unlike BMW’s active steering system, which employs a planetary gearbox, Lexus’s Variable Gear Ratio Steering (VGRS) uses something called a wave generator and a flexible gear. Lexus claims its system is more accurate and quicker acting than others. VGRS can be found on the LS sedan, the LX SUV, and the new GS F Sport. We sliced into the unit to get an idea of  how it works and because we wanted to find out what a wave generator is.