This system uses a low-speed cam to actuate the intake valve during low engine speeds, and a high-speed cam to actuate the intake valve during high engine speeds. As a result, this system realizes further improvement in low-speed torque and high-speed power output over the conventional engine.
    The low-speed cam has a shorter valve overlap and valve-opening duration, and possesses characteristics that are well-suited to low-speed operations in which the intake air inertia is small. The high-speed cam has a longer valve overlap and valve-opening duration, and possesses characteristics that are well-suited to high-speed operations in which the intake air inertia is large. When the engine is operating at low speeds (below 3,500 rpm), the oil control valve is OFF (duty cycle ratio: 0%). Therefore, the cam switching control piston remains down, allowing the intake valve to be actuated by the low-speed cam. The low-speed cam consists of two cams with different valve lifts, and the two cams actuate one intake valve each. For this reason, a difference is created between the valve lifts, creating a more powerful flow of air-fuel mixture and stabilizing combustion in the cylinder. As a result, low fuel consumption, low exhaust gas emissions, and high torque have been realized.
When the engine is operating at high speeds (above 3,500 rpm), the Engine-A/T-ECU turns on the oil control valve (duty cycle ratio: 100% for 2 seconds while switching, and 60% after 2 seconds have elapsed). Consequently, the hydraulic pressure acts on the cam switching control piston, causing the high-speed cam to actuate the intake valve. As a result, the valve opening duration and the valve lift increase, effectively increasing the intake air volume and the power output.
Under the conditions indicated below, the low-speed cam always operates the intake valve:

• Engine coolant temperature below 20°C

• Within 10 seconds upon starting the engine