The valves are set up to open and close at exactly the right moment. One lets the fuel mixture in and closes. After the fuel explodes and pushes the piston down, the other valve lets the exhaust out. The visor is a flat sunshade and is usually movable. It is attached to the interior of the car at the top of the windshield.
Visors protect the eyes of the driver and passengers from the sun's glare.
The voltage regulator controls voltage and current output of the alternator by automatically cutting resistance in or out of the field circuit to keep it in a safe value. Varying the resistance alters the amount of current passing through the field. When the battery becomes fully charged, the resistance is cut into the field circuit and the charging rate is decreased. In electromagnetic regulators, the voltage regulator unit limits voltage output by controlling the amount of current applied to the rotating field. The field relay on these regulators connects the alternator field windings and voltage regulator windings directly to the battery.