HOW IT WORKS
The essence of Twin Disc’s QuickShift transmission is its patented clutch. Compare the diagrams showing a standard marine gear and QuickShift below, paying particular attention to the pistons. While a standard clutch has flat-faced pistons, QuickShift's pistons are stepped-face, with a big O-ring separating a large piston area from a smaller, central one. Why? Using hydraulic oil (shown in yellow) to actuate a single, relatively large, flat-faced piston in a standard transmission from a relaxed or neutral position to full, clutch-plate lockup on a transmission shaft (see A in both diagrams) tends to be both slow and mechanically jarring. However, using oil to actuate only a small piston area (E in the QuickShift diagram) to achieve a semi-clutch-plate lockup that’s useful at slower speeds is faster and smoother. And using more oil to actuate the large piston area as well when necessary (See F in QuickShift diagram) via a pressure-activated sequencing valve (see D in QuickShift diagram) to achieve full clutch-plate lockup for high speeds maintains the faster clutch response and lack of shock. What's more, because only the small piston area is actuated for slower speeds (during which the clutch plates slip under reduced load), QuickShift can slow propellers to as little as 50 rpm. Such fine-tuning, of course, expands the range of maneuverability available to either a conventionally oriented boathandler or a joystick-enabled one. —B.P.
This article originally appeared in the January 2010 issue of Power & Motoryacht magazine.