Valve camshaft is part of the engine, responsible for driving the valve open and closed on time, the role is to ensure that the engine cylinder at work regularly for the inhalation of the fresh combustible mixture, and timely discharge of combustion exhaust cylinder. Camshaft drive directly through the valve rocker arm, it is suitable for high-speed car engine, the speed is high, in order to ensure the intake and exhaust and transmission efficiency, simplify the transmission, reducing the high speed of vibration and noise, the use of overhead valve and overhead camshaft, so that the structure of the engine is relatively compact. However, everything has two sides, overhead camshaft drawback is due to the layout design of complex parts, repair it is also more trouble. But measuring the pros and cons, it is more suitable for cars.

Car engine in accordance with the number of overhead camshaft, single overhead camshaft and is divided into DOHC. When using more than two valves per cylinder, the valve arranged in the form of generally two types:

The first hybrid intake valve and exhaust valve are arranged in a camshaft that a single overhead camshaft (SOHC) the other is the intake valve and exhaust valve on the breakdown of the two camshafts.The former all-valve driven by a single camshaft through the mandrel, but the location of the inlet valves are different, so the accuracy can not maintain the action, the effect is somewhat less certain, which does not have this drawback, you can get more good performance, but need more equipped with a camshaft, which is double overhead camshaft (DOHC), new engine introduced in recent years, many use this form. In general, DOHC movement of relatively high, F1 cars used more often, but because of manufacturing process complexity, high cost; SOHC relative configuration simpler, better use of the durability of not only the driving force can adapt to general customer requirements, can also adapt to the requirements of its economy.