Smart engine system...sounds like it should come with a degree. Actually,
the science lies in variable valve timing, and something techies call "cam
phasing." Which just sounds cool.
Engines equipped with Variable Valve Timing have special lubrication
and maintenance requirements. Neglecting the vehicle manufacturer’s
service recommendations can result in major engine performance
deficiencies. Imagine changing the oil and filter on a vehicle and
having it return with some major driveability symptoms,in addition
to an illuminated Check Engine Lamp and multiple codes stored in the
PCM memory. Trust me… it can happen. Should this occur, it may
require more than draining and installing the correct viscosity oil
to return the vehicle to service. Read on to have a better appreciation
of how the camshaft arrangement functions, and the importance of the
proper viscosity oil and a scheduled maintenance for the vehicle.
Some vehicle manufacturers are equipping their engines
with a variable valve timing system, which allows a continuous
adjustment to the camshaft, referred to as cam phasing.
This system allows adjustments to the valve overlap during
all driving conditions to achieve optimum performance and
fuel economy,while lowering the emission output. This arrangement
has resulted in some vehicle manufacturers eliminating
the EGR valve. GM advises that the camshaft position actuator
allows the camshaft sprocket to change its position by
as much as 50 degrees in relation to the camshaft on their
system. GM applications utilize one of two systems that
function in accordance with the following descriptions
provided by GM:
Spline Phaser System… On
this system the components include the powertrain control
module (PCM), pulse-width modulation (PWM) control valve,
cam phaser, and camshaft position (CMP) sensor. The PCM
controls the PWM valve, which directs engine oil in front
of or behind the piston in the cam phaser actuator, in
relation to engine speed and manifold absolute pressure
(MAP) sensor inputs. Improper camshaft position can result
in violent detonation or loss of power. (See Fig.1)
 Vane Phaser System… This
design system utilizes a four vane-type camshaft position
(CMP) actuator,which includes integral control valves and
electromagnets. This system is controlled in the same manner
as the spline phaser via a control valve; however, the
internal components differ. Instead of using an internal
piston with splines, a rotor with four vanes is connected
to the end of the camshaft. The rotor is housed inside
the stator, which is bolted to the cam gear (See Fig. 2).
The rotor and stator are not mechanically attached, as
with the splined phaser. Instead, they are connected via
a hydraulic link, as oil pressure is controlled on both
sides of the rotor vanes. By varying the balance of oil
pressure on either side of the vanes, the camshaft position
can be controlled. A return spring is positioned under
the reluctor of the phaser to help return it to a 0 degree
position.
The CMP actuator system is comprised of four actuator solenoids, four control
valves, four vane style CMP actuators and four CMP sensors. The CMP actuators
consist of a housing with an integral cam drive sprocket and cam sensor target
wheel. Positioned inside the housing is a four-lobed vane with oil pressure
chambers on both sides of each lobe. The four-lobed vane is bolted to the front
of the camshaft and controlled by an integral oil control valve. On systems
that use the electromagnet, the PCM sends a 12 volt PMW signal to the electromagnet
to activate the oil control valve. The oil control valve ports the pressurized
engine oil to either the advancing or retarding chambers of the CMP actuator
to change the camshaft position relative to the crankshaft position, as commanded
by the PCM. The cam phasing is continuously variable within a range of 40 degrees
for the intake valve timing and 50 degrees for the exhaust valve timing. When
the engine is not running or when the CMP actuators are not commanded, the
exhaust CMP actuators are parked at the full advance position and the intake
CMP actuators are parked at the full retard position. The PCM calculates the
optimum camshaft position based on engine speed, manifold absolute pressure,
throttle position, crankshaft position, camshaft position, engine load and
barometric pressure.
Ford’s Variable Camshaft Timing
Ford refers to their system as VCT (Variable Camshaft Timing). In a general
overview, this system functions in much the same manner as the GM system,
in that it enables a re-positioning of the camshaft(s) in relation to crankshaft
rotation.
Ford identifies itself with four different types of VCT systems:
1) EPS (Exhaust Phase Shifting): With this system, the exhaust
cam is the active cam being retarded.
2) IPS (Intake Phase Shifting): On this system, the intake
cam is the active cam being advanced.
3) DEPS (Dual Equal Phase Shifting): With this arrangement,
both the intake and exhaust cams are phase shifted and equally advanced or
retarded.
4) DIPS (Dual Independent Phase Shifting): Both cams are shifted
independently.
The previously mentioned systems incorporate four operational modes:
-
Idle
- Part Throttle
- Wide Open Throttle
- Default Mode
During idle or low engine RPM with a closed throttle position, the PCM determines
the phase angle based on air flow, oil temperature and engine coolant temperature.
During part throttle and wide open throttle, the PCM determines the phase angle
based on engine RPM, load and throttle position. The VCT system provides an
increase in power, fuel efficiency and lower emission output. The IPS system
provides improved engine torque. On some applications, Ford has eliminated
the EGR system with the VCT system. Elimination of the EGR valve is accomplished
by controlling the intake and exhaust valve overlap.
The VCT system functions by controlling the flow of engine oil in the VCT actuator.
The PCM controls the duty cycle of the VCT solenoid, which affects the pressure
and flow of the oil in the VCT actuator, thereby advancing or retarding the
camshaft timing. One half of the actuator is coupled to the camshaft and the
other half is connected to the timing chain/gear.Oil chambers between the two
halves couple the camshaft to the timing chain.When the flow of oil is directed
from one side of the chamber to the other, the pressure change forces the camshaft
to rotate in an advance or retard position, depending on the direction of the
oil flow.
Correct Oil Viscosity and Good Maintenance
It is imperative that only the vehicle manufacturer’s recommended oil
viscosity be installed in a vehicle equipped with variable valve timing. The
GM applications reflect 5W30 and Ford recommends 5W20. We have encountered
a situation whereby 20W50 oil was installed by a lube tech who was unfamiliar
with this system. Days later, the vehicle was towed to the dealer and the repairs
were not covered under warranty. The diagnosis was a lengthy process, as the
Check Engine Light was illuminated and multiple codes were stored in memory.
Once the technician determined the performance condition occurred following
a routine lube service, he went straight to the problem. Draining the crankcase
and installing the correct viscosity oil returned the system to normal operation.The
lube shop was responsible for the dealer’s diagnostic charges,
plus a new oil change.
Very Important: Clean, pressurized engine oil of the
vehicle manufacturer’s recommended viscosity is essential in order
to provide proper system operation. Make certain the crankcase is properly
filled and the oil level is within normal operating range. Never allow
the oil to become contaminated due to neglect of maintenance, or through
the addition of additives that can affect the viscosity of the lubricant.
Engine oil pressure, oil viscosity, temperature and oil level can affect
the operation of engines fitted with this camshaft arrangement.
LARRY HAMMER
Technical Services
Mighty Distributing System of America
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