Ford Gets Phased -- Using Free Energy
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Variable valve timing is ancient history. You already know that twiddling the intake and exhaust valve timing and overlap helps broaden an engine's torque curve and that most engines do this by inserting a gizmo in between the camshaft and the pulley for the timing chain or belt. And as you well know, this widget uses engine oil pressure to advance or retard the cam relative to its pulley.
What you may not know is that relying on engine oil pressure limits the performance of these "cam phasers" at engine start-up, when the oil is cold and thick, and at low engine speeds when the pump isn't producing much pressure. Well the clever engineers at Ford noticed the oil pressure in the chambers that move the cam one way or the other experiences a little wiggle before and after each cam lobe opens its valve. That's because the high pressure of the valve spring wants to slow the lobe down just before it pushes the valve fully open, and then tries to speed it up when the valve starts closing. Instead of fighting this back-and-forth wiggling, Ford decided to harness it, using these little pressure pulses to advance or retard the cam.
The system is elegantly simple. Engine oil pressure is fed to the cam phaser, but very little or no oil flows to it or through it. Instead, the pressure needed to move in one direction is supplied by the pressure spikes from the opposite chamber and vice versa. A simple three-position spool valve allows oil to flow in either direction or not at all. The system works a bit like a ratchet wrench.
This Cam-Torque Actuated variable valve timing system reportedly reduces oil-pump flow requirements by 25% relative to conventional VVT systems, for a claimed fuel-economy boost of 0.4% on Ford's 3.0L Duratec V-6-powered Fusion (CTA's first application). But the real benefit is that the system can start rotating the cam about 350 rpm earlier than oil-pump-pressure systems and can ramp up much faster, achieving the full 47 deg (crankshaft angle) advance by 1500 rpm -- that's 40 deg more advance at that point than the old system. The overall net result (other engine improvements include tweaks to the cylinder head and intake for better breathing, 10.3:1 compression, and flex-fuel capability) is an extra 19 hp and 23 lb-ft of torque with improved fuel economy (thanks largely to the new six-speed automatic). Expect this elegantly simple and cost-effective system to migrate throughout Ford's VVT engine lineup.
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