Dual-mode, viscous crankshaft vibration damper

A viscous torsion damper comprising:

• a central hub;
• an annular working chamber surrounding and connected to said central hub;
• a first annular inertia mass closely coupled for lateral vibration to an inside annular surface of said working chamber, said first annular inertia mass having a friction reducing bearing surface against said inside annular surface of said working chamber;
• a second annular inertia mass arranged entirely radially outward from and concentric of said first annular inertia mass and defining a gap therebetween;
• said first and second inertia masses moveable relative to said central hub within said annular chamber defining one or more shear planes therebetween;
• a resilient damping element arranged within said gap mechanically coupling said first and second inertia masses via friction for damping lateral vibration, said resilient damping element spaced from said one or more shear planes;
• and
• a viscous fluid disposed at least between said second inertia mass and an inside surface of said working chamber.