Camshaft Actuator System Description (LDE)
Circuit/System Description
The camshaft position actuator solenoid valve - Intake and
camshaft position actuator solenoid valve - exhaust system enables
the engine control module (ECM) to change camshaft timing while the
engine is running. The camshaft position actuator assembly varies
camshaft position in response to directional changes in oil
pressure. The camshaft position actuator solenoid valve - Intake
and camshaft position actuator solenoid valve - exhaust controls
the oil pressure that is applied to advance or retard the camshaft.
Modifying camshaft timing under changing engine demand provides
better balance between the following performance concerns:
• |
Lower exhaust emissions
|
The camshaft position actuator solenoid valve - Intake and
camshaft position actuator solenoid valve - exhaust is controlled
by the ECM. The crankshaft position sensor and the camshaft
position sensor - intake and camshaft position sensor - exhaust are
used to monitor changes in camshaft position. The ECM uses
information from the following sensors in order to calculate the
desired camshaft position:
• |
The engine coolant temperature
(ECT) sensor |
• |
The mass air flow (MAF)
sensor |
• |
The throttle position
sensor |
• |
The vehicle speed sensor
(VSS) |
Camshaft Position Actuator System Operation
The ECM operates the camshaft position actuator solenoid valve -
Intake and camshaft position actuator solenoid valve - exhaust by
pulse width modulation (PWM) of the solenoid coil. The higher the
PWM duty cycle, the larger the change in camshaft timing. Oil
pressure that is applied to the advance side of the fixed vanes
will rotate the camshaft in a clockwise direction. The clockwise
movement of the camshaft will advance the timing up to a maximum of
21°. When oil pressure is applied to the return side of the
vanes, the camshaft will rotate counterclockwise until returning to
0°.
Oil flowing to the camshaft position actuator solenoid valve -
intake and camshaft position actuator solenoid valve - exhaust
housing from the camshaft position actuator solenoid valve - Intake
and camshaft position actuator solenoid valve - exhaust advance
passage applies pressure to the advance side of the vane wheel in
the camshaft position actuator assembly. At the same time the
camshaft position actuator solenoid valve - Intake and camshaft
position actuator solenoid valve - exhaust retard passage is open,
allowing oil pressure to decrease on the retard side of the vane
wheel. These two simultaneous actions cause the vane wheel to
rotate clockwise, advancing camshaft advance timing.
When the oil flowing to the camshaft position actuator solenoid
valve - Intake and camshaft position actuator solenoid valve -
exhaust housing is from the camshaft position actuator solenoid
valve - Intake and camshaft position actuator solenoid valve -
exhaust retard passage , oil pressure is applied to the retard side
of the vane wheel. Because the solenoid advance passage is open,
allowing oil pressure to decrease on the advance side of the vane
wheel, the camshaft position retards.
The ECM can also command the camshaft position actuator solenoid
valve - Intake and camshaft position actuator solenoid valve -
exhaust to stop oil flow from both passages in order to hold the
current camshaft position. The ECM is continuously comparing
camshaft position sensor - intake and camshaft position sensor -
exhaust input with camshaft position actuator solenoid valve -
Intake and camshaft position actuator solenoid valve - exhaust
input in order to monitor camshaft position and detect any system
malfunctions. The following table provides camshaft phase commands
for common driving conditions:
Driving Conditions
|
Change in Camshaft Position
|
Objective
|
Result
|
Idle
|
No change
|
Minimize valve overlap
|
Stabilize idle speed
|
Light engine load
|
Retard valve timing
|
Decrease valve overlap
|
Stable engine output
|
Medium engine load
|
Advance valve timing
|
Increase valve overlap
|
Better fuel economy with lower emissions
|
High RPM with heavy load
|
Retard valve timing
|
Retard intake valve closing
|
Improve engine output
|
|
|
|