C15 and C18 – Variable Valve Actuator

The Intake Valve Actuation system (IVA) uses pressurized engine oil to delay the closing of the intake valves. The system is controlled by the Engine Control Module (ECM). The system contains the following components:

Check Valve (53) – Pressurized engine oil flows to a rail inside the valve cover base. A check valve prevents oil from flowing from the rail back to the main oil gallery.

Pressure Sensor (52) – A pressure sensor is threaded into the rail. The sensor converts the rail pressure into an electrical signal. The ECM monitors the signal in order to determine the pressure of the oil in the rail.

Control Valve (51) – A control valve is threaded into the rail. The control valve contains a coil and a cartridge assembly. The cartridge assembly contains a spool. The spool is normally closed. When the spool is closed, the oil is contained in the rail. The ECM sends a signal to the coil in order to fully open the spool. The oil is released into the space underneath the valve cover and the rail pressure is reduced.

Actuator (54) – The actuators are located under the valve covers. Pressurized engine oil flows from the rail to each actuator. The actuators use the pressurized engine oil and electrical commands from the ECM in order to delay the closing of the intake valves.


Illustration 9 g02760139
Component location

(51) Control valve

(52) Pressure sensor

(53) Check valve

(54) Actuators

System Operation During Engine Start

The ECM performs the following sequence of operations when the engine is started:

The ECM commands the control valve to open for 17 seconds.
The ECM checks the temperature of the coolant.
The ECM commands the control valve to close when the coolant temperature exceeds 20 °C (68 °F). This allows the temperature of the oil in the rail to warm up.
The ECM commands the control valve to open. The ECM samples the rail pressure. The ECM commands the control valve to close. The ECM takes a second sample of the rail pressure. The ECM compares the two pressure values. The ECM activates a code if the pressure difference is too low.
The control valve should remain closed during engine operation.
System Operation During Engine Operation

The system does not operate until the engine has reached normal operating temperature.


Illustration 10 g02760158
Section view of the components

(54) Actuator

(55) Space

(56) Solenoid

(57) Piston

(58) Rocker arm

(59) Valve

(60) Rail

(61) Intake valves

Each actuator (54) contains two solenoids (56). Each solenoid is connected to a valve (59). The solenoid is normally de-energized. The valve is normally open. This allows oil to flow between rail (60) and the space (55) above piston (57) .

Rocker arm (58) is down when the intake valves are open. Pressurized oil flows from rail (60) to space (55) above piston (57). This causes the piston to move down. The piston contacts rocker arm (58) .

The ECM energizes solenoid (56) when the ECM requires intake valves (61) to remain open. The energized solenoid closes valve (59). This traps the oil in space (55). The trapped oil causes piston (57) and rocker arm (58) to remain down. This keeps intake valves (61) open.

The ECM de-energizes solenoid (56) when the ECM requires the intake valves to close. The de-energized solenoid lifts valve (59). Valve springs (59) raise intake valves (61), rocker arm (58), and piston (57). The piston that is rising forces the oil from space (55) into the rail (60) .

The flow of oil into the rail changes the pressure of the oil in the rail. The ECM monitors the rail pressure. The ECM determines if the changes in rail pressure are correct for the commands that were sent to a particular solenoid. The ECM activates a diagnostic code for the appropriate cylinder if the changes in rail pressure are incorrect for that solenoid.

Posted in C18

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