New Technology in Lincoln car
Cam-Torque
Actuated Variable Valve Timing System
Cam Phasers, Activate! BorgWarner's new approach to
variable valve timing is cam-torque actuated.
Most
modern variable valve-timing (VVT) systems use a cam phaser that rotates the
position of each camshaft relative to the timing chain. Think of making a
record turntable go faster or slower by spinning it with your hands. The cam
phaser has two basic components: an outer sprocket connected to the timing
chain and an inner rotor (connected to the camshaft) that varies the valve
timing by adjusting the rotation angle of the cam.
This inner rotor consists of a set of lobes, and oil fills the
space between the outer housing and the lobes. Left alone, the rotor will
simply spin at the same rate as the outer housing. If you add oil to one side
of the lobe and remove it from the other, the rotor moves, and—voilà!—there’s your variable valve timing.
The
majority of these VVT systems use oil pressure to push the rotor back and
forth, but BorgWarner thinks its cam-torque-actuated (CTA) system marks an
important step forward. Oil-pressure-actuated (OPA) systems require an upsize
oil pump to produce the extra pressure that’s required to work the cam
phasers, which saps some of the fuel-economy gains of VVT. With a mechanical
oil pump, OPA systems don’t work well at low engine speeds because the pump
doesn’t build pressure and volume until the revs get higher.
The CTA
system avoids those pitfalls by using Newton’s Third Law of Motion—for every
action there is an equal and opposite reaction—to move the oil in the cam phasers.
When a cam lobe pushes a valve open, the valve spring resists that force and
pushes back. Similarly, when the valve spring pushes a valve closed, it also
pushes on the cam lobe in the opposite direction from the valve opening. When
multiplied over an entire camshaft, there is enough energy from these
back-and-forth forces to make cam phasing work.
Another
trick to BorgWarner’s system is the way it moves oil. A center spool valve,
controlled by a solenoid inside the cam-phasing rotor, directs the flow. With
the valve open in one direction, oil flows into only one side of the oil
pockets and can’t leave. By sliding the valve back and forth, the system can
mete out the precise amount of oil flow on either side of the rotor lobes.
The key
advantages of the CTA system are that it responds quickly even at idle and can
operate using a standard engine’s oil pump. But there are downsides. As engine
speeds increase, the CTA system becomes less effective. This happens because
the valve events occur more frequently, reducing the time available to move
the oil. Conversely, OPA systems work better as oil pressure increases and
are better at high rpm. So there’s not much of a peak power gain from a CTA
system; it improves performance and efficiency in other areas of the rev range.
Also, CTA cam phasing is at the mercy of the natural oscillations of those
forces on the camshaft. Valve openings and closings in an inline-six are spaced
too closely for the system to work well. But a V-6 (or inline-three) is
perfectly suited because there isn’t as much overlap between each valve event.
The system also works on V-8 engines.
CTA variable valve timing debuted on Ford’s 3.0-liter Duratec
V-6, beginning with the 2009 Escape and the 2010 Fusion. The
3.7-liter V-6 in the Mustang uses BorgWarner’s system, too, as do the 2011 Edge and Lincoln MKX.
LINCOLN MKX WITH CAM TORQUE ACTUATED VARIABLE VALVE
TIMING SYSTEM (CTA VVT)
CTA Phasers with Mid
Position Lock
To provide engine designers with even wider
calibration opportunities, Morse TEC developed CTA phasers with a patented mid
position lock. This technology employs a hydraulic circuit to passively move
the system, allows an increased range of camshaft positioning and features a
default stop at an intermediate position within an expanded range of
travel.
CTA phasers with mid position lock can
improve fuel economy up to 4% compared with conventional VCT systems. The
innovation also features a failsafe to ensure the phaser returns to the middle
position, even after an engine stall. The benefits: reliable engine starts in
nearly any potential operating condition with no added active relocking
control.
Features & Benefits
• Suitable for all OHC engine types
• Uses camshaft torque to actuate
• Fast actuation independent of engine oil pressure or RPM
• Actuates during engine cranking
• Suitable for start/stop engine applications
• Industry leading actuations rates
• Enables late intake valve closing strategies
• Available with mid-position lock
• Large range of authority up to 120° crank
• Reduces engine parasitic losses
• Increased fuel economy
• Lower emissions
•
Improved vehicle performance
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