Compass 2WD L4-2.0L VIN 0 (2007)
Variable Valve Timing Solenoid: Description and Operation
Operation
OPERATION
There is both an Intake and an exhaust camshaft sensor on vehicles equipped with a World Engine. The variable valve timing system used on World
Engines requires the exact position of both the intake and exhaust camshaft. The GPEC1 uses camshaft sensor data along with crankshaft data to
determine the actual position of the camshafts. Intake and exhaust phaser oil control valves are required on World Engine vehicles using variable valve
timing. The oil valves direct oil to the Intake and exhaust phasers. Oil pressure in the phasers moves the camshafts to an advanced or retarded position.
To resolve this inherent conflict between optimum high and low speed valve timing, the GPEC1 controlled engine uses a variable valve timing system.
The variable valve timing system advances and retards valve timing by rotating the position of both the intake and exhaust camshafts. With this system,
the intake valve opening can range from 80 to 120 crankshaft degrees after Top Dead Center. Likewise, the exhaust valve opening can range from 85 to
120 crankshaft degrees before Top Dead Center. This degree of flexibility provides many benefits, including: Improved Engine Performance, Increased
Fuel Economy, Improved Idle Stability and Decreased Engine Emissions. In non operating condition, the camshaft stays in lockpin position of cam
phases. This is 120 degrees ATDC for intake camshaft and 120 degrees BTDC for exhaust camshaft.
The variable valve timing system is electronically controlled and hydraulically operated. The GPEC1 receives information from many sensors to
determine the optimum valve timing. It then pulse-width modulates oil control valves which direct oil to the cam phasers. The cam phasers use oil
pressure to rotate the intake and exhaust camshafts. The rotation of the camshafts is referred to as cam phasing. Before the GPEC1 can begin
commanding the camshaft phasing, several enabling conditions must be met:
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The engine oil temperature must be at least -6.6° C (20° F)
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The oil control valve coil temperature must be less than 140° C (284° F)
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Engine speed must be at least 600 to 1000 rpm to achieve minimum oil pressure.
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Battery voltage must be at least 10 volts
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And there must be no camshaft or crankshaft sensor faults, engine timing faults, or oil control valve faults
First we will examine variable valve timing enabling conditions, and then we will take a closer look at the inputs and outputs of the system:
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Accelerator pedal position sensor
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Oil temperature sensor
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Map sensor
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Intake cam sensor
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Exhaust cam sensor
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Crankshaft sensor
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GPEC1
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Exhaust phaser oil control valve
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Intake phaser oil control valve
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Inputs
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Engine control module
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Outputs
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Sensed battery voltage
A minimum oil temperature is required to enable variable valve timing operation. Oil temperature and viscosity also have an impact on the operation of
variable valve timing after start-up. Oil is used to control the movement of the camshafts. An incorrect oil viscosity could adversely affect the operation
of the system or even render the system inoperative. It may even set a fault code.
The accelerator pedal position sensor indicates how far the driver wants to open the throttle plate. The GPEC1 calculates an initial camshaft set point
based on whether the accelerator pedal is at part throttle or wide open throttle.
The MAP sensor provides information regarding engine load.
Sensed battery voltage provides information regarding current system voltage. Sensed battery voltage must be at least 10 volts in order for the oil
control valves to function properly.
This information allows the GPEC1 to adjust camshaft timing to achieve the best fuel economy, the best engine performance or a combination of both.
The hall-effect crankshaft sensor provides RPM information and determines when the number one piston is approaching Top Dead Center. The sensor
generates a signal as the tone wheel, attached to the crankshaft, rotates. The tone wheel has 60 teeth minus two. When the gap, created by the missing
teeth passes by the sensor, a signal is produced that indicates the number one piston is at Top Dead Center. The GPEC1 uses crankshaft sensor data
along with camshaft data to determine the actual position of the camshaft. There are two hall-effect camshaft sensors on engines equipped with variable
valve timing. The GPEC1 uses camshaft sensor data along with crankshaft data to determine the actual position of the camshaft.
The GPEC1 individually controls each valve. It sends a pulse width modulated signal to move a spool within the outer casing of the valve. Depending
upon spool movement, oil is directed through the passages to advance or retard cam timing. The oil control valve also has a special cleaning strategy at
