HYDRAULIC VARIABLE VALVE TIMING CONTROL [SKYACTIV-G 2.0]

2016 – MX-5 – Engine

Changes the exhaust valve timing according to the engine operation conditions to improve the engine output, fuel economy, and emission performance.
Based on each input signal, the PCM determines the optimum exhaust valve timing according to the engine operation conditions, drives the OCV, and switches the oil passages of the hydraulic variable valve timing actuator to optimally control the exhaust valve timing.
Based on the coordination with the electric variable valve timing control and by increasing the amount of overlap during high engine loads, nitrogen oxide (NOx) occurring largely at high temperatures is reduced by re-circulating exhaust gas into the combustion chamber, which also reduces combustion temperature.

Exhaust valve timing determination

The PCM controls current to the OCV to obtain optimum exhaust valve timing according to the engine operation conditions (target exhaust valve timing).
In addition to controlling the OCV drive current value to obtain the target exhaust valve timing, the PCM compares the value with the actual exhaust valve timing to correct the OCV drive current value if necessary.

Target exhaust valve timing

The target exhaust valve timing is determined by the engine speed and the charging efficiency.

Actual exhaust valve timing

The actual exhaust valve timing is calculated by subtracting the cam maximum advance learning value from the value (retard amount) detected by the exhaust CMP sensor and CKP sensor.

Cam maximum advance learning value

Though the exhaust camshaft valve timing (including maximum advance position) is detected based on the difference in the rise between the exhaust CMP sensor and the CKP sensor signals, variation in signals from the assembly of each sensor occurs. As a result, the PCM stores the difference in the rise of the exhaust CMP sensor and CKP sensor signals to prevent detection of variations in the exhaust valve timing.

OCV drive current determination

The PCM divides the OCV drive range into three modes according to engine operation conditions. The OCV drive current is determined based on the target current calculated in each mode.

Range mode table

Mode name	Control description
Feedback mode	The feedback mode constantly monitors whether the actual exhaust valve timing matches the target exhaust valve timing which is determined according to the engine operation conditions, and controls the OCV drive current based on the results. Mode execution condition In modes other than cleaning mode or maximum cam advance mode
Cleaning mode	Cleaning mode is to remove foreign matter in the OCV oil passages. Mode execution condition When any of the following conditions is met: During deceleration fuel cut Engine speed: 2,250―3,500 rpm Engine coolant temperature: 80 °C {176 °F} or more
Cam advance mode	If the cam advance is appropriate according to engine operation conditions such as while in torque down execution during idling, the cam advance mode advances the exhaust valve timing and stabilizes the engine speed. Mode execution condition When any of the following conditions is met: During engine cranking Engine speed: Less than 875 rpm Engine coolant temperature: Less than 35 °C {95 °F} Other conditions such as when maximum advance is appropriate according to engine rotation and load conditions