Tuesday, September 14, 2010

How VVTL-i Works

The Toyota VVTL-i system or "lift" is similar to Honda's VTEC system, incorporating two distinct cam profiles. However, the actual mechanism is quite different. Both cam lobes operate a single wide rocker arm that acts on both intake or both exhaust valves. A needle-bearing roller on the arm follows the low-rpm, short-duration, low-lift lobe, forcing both valves to open and close on that profile.

The roller design and roller bearings on the rocker arm pivot help to minimize valvetrain friction. The high-rpm, higher-duration, longer-lift lobe rubs on a hardened steel slipper follower mounted to the rocker arm with a spring. Even though the high-rpm lobe is pushing down further than the low-rpm lobe, the spring absorbs the extra movement.

At 6000rpm, the ECU sends a signal to an oil control valve at the end of the camshaft that puts oil pressure behind a lock pin in the rocker arm, sliding the pin under the spring-loaded slipper follower, locking it to the rocker arm and forcing the arm to follow the high-rpm cam profile. Below is the animation on how the lift works.