MIVEC (Mitsubishi Innovative Valve timing Electronic Control system) <135 engine>

BASIC OPERATION

• In the MIVEC, the intake camshaft sprocket and the camshaft are designed to slide, and the system regulates the volume of oil that is supplied to the oil chambers (for timing advance and retard), which are provided in the camshaft. Thus, the system varies the valve timing by controlling the phase angle (staggered angle) between the sprocket and the camshaft.
  
• The phase angle between the sprocket and the camshaft is controlled by controlling the duty cycle of the current that is applied to the oil control valve, which is provided in the cylinder head.
  

• The spool valve in the oil control valve moves towards timing advance in accordance with the timing advance control signal from the engine-ECU or engine-A-M/T-ECU.
  
• The oil pressure from the cylinder block enters the advance chamber in the V.V.T. sprocket, and the vane rotor moves towards timing advance, thus causing the intake camshaft (which is coupled to the vane rotor) to advance.
  

• The spool valve in the oil control valve moves towards timing retard in accordance with the timing advance control signal from the engine-ECU or engine-A-M/T-ECU.
  
• The oil pressure from the cylinder block enters the retard chamber in the V.V.T. sprocket, and the vane rotor moves towards timing retard, thus causing the intake camshaft (which is coupled to the vane rotor) to retard.
  

• When the actual phase angle reaches the target phase angle, the advance chamber and the retard chamber hold their oil pressure in order to hold the phase angle of the intake camshaft.
  

OPERATION UNDER VARIOUS DRIVING CONDITIONS

Driving condition	Valve timing	Operation	Effect
Idling		The valve overlap is decreased to minimize the amount of exhaust gas that flows back into the intake port.	Stabilizes idle speed
Low- to medium-speed		The timing to close the intake valve is accelerated to minimize the amount of intake air that flows back into the intake port. This improves volumetric efficiency and increases low- to medium-speed torque.	Improves low- to medium-speed torque
High-speed		The timing to close the intake valve is retarded in accordance with the engine speed, thus controlling the valve timing to suit the inertial force of the intake air and improving volumetric efficiency.	Improves output

OIL CONTROL VALVE CONTROL

• The engine-ECU or engine-A-M/T-ECU assesses the driving conditions by detecting the signals provided by various sensors, and sends duty cycle signals to the oil control valve in accordance with the driving conditions, in order to control the position of the spool valve.
  
• In the oil control valve, the oil pressure is applied to the retard chamber or the advance chamber, in order to continuously vary the phase of the intake camshaft.
  
• When the engine is stopped, the engine-ECU or engine-A-M/T-ECU turns OFF the duty cycle signals, and applies a constant oil pressure to the retard chamber in order to hold the spool valve in the most retarded position.
  

PHASE ANGLE CONTROL

CALCULATING THE ACTUAL PHASE ANGLE

Target Phase Angle The target phase angle is read by way of the map value that is preset for the respective engine speed and target torque. Feedback Correction When the deviation between the target phase angle and the actual phase angle is positive (the valve opens earlier than the target) the actuation duty cycle decreases gradually in order to match the actual phase angle to the target phase angle. On the other hand, if the deviation between the target phase angle and the actual phase angle is negative (the valve opens later than the target), the actuation duty cycle increases gradually in order to match the actual phase angle to the target phase angle. When the deviation between the target phase angle and the actual phase angle is practically zero, the oil control valve (after a learning correction) is actuated with the neutral duty cycle. Actual Phase Angle Correction The actual phase angle when the oil control valve is OFF is stored in learning memory as the minimum phase angle. When the oil control valve is OFF, the actual phase angle is compensated using the deviation between the phase angle 75° and the maximum phase angle (the sensor error), because the intake camshaft sprocket is accurately designed with phase angle 75°.

Actual Phase Angle Correction for Ignition Timing Due to mechanical constraints, the actual phase angle is late in responding to the changes in the target phase angle. Therefore, until the actual phase angle catches up with the target phase angle, the ignition timing is corrected in accordance with the deviation between the target phase angle and the actual phase angle.