Bottom Camshaft

- Feb 14, 2019-

The camshaft layout of the engine is divided into OHC (overhead camshaft) and OHV (bottom camshaft). At present, automobile manufacturers in Japan and Europe prefer the design of overhead camshafts; and the bottom camshafts are usually only visible on American cars.

The OHC (overhead camshaft) has been developed into SOHC (single overhead camshaft) and DOHC (double overhead camshaft). A single overhead camshaft relies on a camshaft to control the opening and closing of the intake and exhaust valves. Generally speaking, the single top is designed with the two-valve engine. Since the two-valve engine has lower intake and exhaust efficiency than the multi-valve, the angular arrangement of the valve is limited. The double overhead camshaft optimizes these problems because a camshaft controls only one set of valves (intake or exhaust), thus omitting the rocker arm of the valve, simplifying the camshaft to the valve. Transmission mechanism. In general, the double overhead camshaft has a high transmission and exhaust efficiency due to the small number of transmission components, and is more suitable for the power performance of the engine at high speed. For Japanese and European manufacturers pursuing high power, the camshaft overhead design is of course the most suitable.

The bottom camshaft is designed to have a large displacement, low speed, and high torque output. Because the bottom camshaft is driven by the crankshaft, then the cam and the rocker arm are connected by a metal rod. The cam jacks up the connecting rod, and the connecting rod pushes the rocker arm to realize the opening and closing of the engine valve. Therefore, the excessively high rotating speed causes the jack to be over-stressed and broken. However, the design of the ejector has its advantages, the structure is simple, the reliability is high, the center of gravity of the engine is low, and the cost is low. Because the engine speed is low and the torque performance is emphasized, the bottom camshaft design is sufficient to meet this demand.

Since the two designs are biased differently, the former is the most powerful, and the latter is the pursuit of high torque. We know that the speed of the car is fast, the traction is strong, and the maximum speed is dependent on the power. There is also a simple formula here: power = speed X torque. The easiest way to increase the power of the engine during naturally aspirated is to increase the speed. The higher the speed, the higher the power will naturally be.