Variable valve timing system (Mazda 6 GG)

Contents: Operation according to driving…⇓ Medium loads ⇓ Heavy load, low to medium speed ⇓ High load, high speed range ⇓ At low temperature ⇓ When starting or stopping the engine ⇓

The variable valve timing system continuously modifies the phases of the variable valve timing actuator and the intake camshaft under the action of hydraulic pressure, which is controlled by the oil control valve (OCV) so that the opening and closing phases of the valves optimally correspond to the operating conditions of the engine. The operation of the oil control valve (OCV) is based on signals from the camshaft position sensor according to the operating conditions of the engine. It controls the hydraulic pressure acting on the variable valve timing actuator.

Operation according to driving conditions: idle, light loads

By reducing overlap, less combustion products are returned to the cylinder. This stabilizes the idle speed, improving fuel economy, and also ensures stable engine operation at low loads.

Fig. 2.30. Diagram of changes in valve timing for different engine operating ranges: 1 – load; 2 – engine speed; 3 – idle speed range; 4 – low load range; 5 – medium load range; 6 – range of high loads of low and medium speeds; 7 – high load and high speed range; 8 – full load operation

Medium loads

The overlap increases and the EGR ratio in the cylinder increases, thereby reducing friction losses (pumping losses), the combustion temperature decreases and the amount of CO in the exhaust gases decreases. The amount of hydrocarbon emissions also decreases due to the re-burning of unignited gas.

Heavy load, low to medium speed

The intake valves close early, resulting in high volumetric efficiency, while improving torque in the low- and mid-speed range.

High load, high speed range

The intake valves close later, high volumetric efficiency ensures maximum power.

At low temperature

Overlap is minimized to prevent combustion products from entering the cylinders and reduce the amount of additional fuel injected into the cylinders. This improves fuel economy and stabilizes high idle speeds.