What is the principle of BMW's dual camshaft variable valve timing? I just saw a solenoid valve on the intake and exhaust camshafts?

These two solenoid valves are variable valves that adjust the intake and exhaust timings. The motor is used to adjust the opening height of the intake valve to control the relative throttle adjustment. The motor is under the trim panel of the engine. Solenoid valve is used to control oil pressure to change the position of camshaft relative to the original position, thus changing the opening and closing time of intake valve and exhaust valve, which is similar to other cars. It has only one adjustable intake valve height to adjust the intake air.