Performance, torque, idle characteristics and exhaust emissions reduction are improved by Variable Camshaft Timing (VANOS). The VANOS unit is mounted directly on the front of the cylinder head and adjusts the Intake and Exhaust camshaft timing from retarded to advanced. The ECM controls the operation of the VANOS solenoid which regulates the oil pressure required to move the control piston. Engine RPM, load and temperature are used to determine VANOS activation.

VANOS mechanical operation is dependent on engine oil pressure applied to position the control pistons. When oil pressure is applied to the control pistons (regulated by the sole-noids), the pistons move causing the splined adjustment shafts to move. The straight splines slide within the camshaft sleeves. The helical splines rotate the camshaft drive sprockets changing the position in relation to the camshaft position which advances/retards the intake/exhaust camshaft timing.

Vanos  The operation of the VANOS solenoid is monitored in accordance with the OBD II require-ments for emission control. The ECM monitors the final stage output control and the signal from the Camshaft Position Sensors for VANOS operation.

Dual VANOS consists of the following parts:
• Intake and exhaust camshafts with helical gear insert
• Sprockets with adjustable gears
• VANOS actuators for each camshaft
• 2 three-way solenoid switching valves
• 2 impulse wheels for detecting camshaft position
• 2 camshaft position sensors (Hall effect)
Vanos operation

  When the engine is started, the camshafts are in the “failsafe” position (deactivated). The intake camshaft is in the RETARDED position – held by oil pressure from the sprung open solenoid. The exhaust camshaft is in the ADVANCED position – held by a preload spring in the actuator and oil pressure from the sprung open solenoid.

  After 50 RPM (2-5 seconds) from engine start, the ECM is monitoring the exact camshaft position. The ECM positions the camshafts based on engine RPM and the throttle position signal. From that point the camshaft timing will be varied based on intake air and coolant temperatures.

  The dual VANOS system is “fully variable”. When the ECM detects the camshafts are in the optimum positions, the solenoids are modulated (approximately 100-220 Hz) maintaining oil pressure on both sides of the actuators to hold the camshaft timing.

Vanos 3

If the VANOS camshaft system goes to the failsafe mode (deactivated) there will be a noticeable loss of power.

 

Camshaft Sensor

The camshaft sensor registers the position of the camshaft with the aid of a sheet metal wheel with various apertures screwed to the camshaft. It operates in accordance with the Hall effect principle.

Hall effect

A permanent magnet in the sensor produces a magnetic field. A conductor with current flowing through it is located in this magnetic field. An electric voltage dependent on the strength of the magnetic field is produced in this conductor perpendicular to the current and perpendicular to the magnetic field. The magnetic field in the sensor is varied by the camshaft sensor wheel and its apertures rotating passed the sensor. The teeth and gaps on the sensor wheel can be recognized by means of the voltage.

Use of the camshaft sensor

It is necessary for the fully sequential injection system (fuel injection takes place individually for each cylinder at the specific firing point).

The variable camshaft control requires feedback of the current position of the camshaft for adjustment purposes.

Variable camshaft timing control VANOS

The VANOS control unit serves the purpose of increasing torque in the lower and medium engine speed ranges. Reduced valve overlap results in lower residual-gas quantities while idling. Nitrous oxide components are reduced by internal exhaust-gas recirculation in the partial load range. This achieves faster heating of the catalytic converters, lower untreated emissions after cold starting and reduced fuel consumption.

VANOS intake/exhaust

A regulated VANOS control unit for intake and exhaust is fitted in this engine. It is activated by means of an electromagnetically operated 4/3-way valve.

The required position of the intake and exhaust camshafts is calculated from the engine speed and load signal depending on the intake air and engine temperature and the VANOS VANOS adjustment unit is controlled accordingly by the engine control unit. The inlet and exhaust camshafts can be variably controlled within their maximum adjustment range, i.e. any arbitrary positions are possible corresponding to the specified values of the engine control unit. When the relevant optimum camshaft position is reached, the solenoid valves maintain a constant oil volume in the adjustment cylinder on both sides of the chamber so that the camshafts remain in the corresponding positions.

When the engine starts up, the intake camshaft is in its end position, i.e. it is initially in the retard position. During engine start, the exhaust camshaft is held in the advance position by means of a spring.

 

Wiring, Camshaft Sensors:

Camshaft Wiring

Wiring, Vanos Solenoids:

Vanos Solenoid wiring