1, OHV
in the form of cam arrangement
into the engine OHC (overhead cam) and OHV of (underfloor camshaft) both. Currently, Japan and European car manufacturers are more favored overhead camshaft This design; and bottom-mounted camshaft, usually we only see the car in the United States.
In understanding the difference between OHC and OHV, we briefly from technical knowledge, look at their respective structure and characteristics:
OHC (overhead cam), after the development is now divided into a SOHC (single overhead camshaft) and DOHC (double overhead camshaft). Rely on a single overhead camshaft is a camshaft to control the intake and exhaust valves opening and closing. Typically the top is in line with the single two-valve engine design, since the two intake valves of the engine, exhaust efficiency lower than the multi-valve, the valve is disposed between the large angle limitations. While the DOHC will be able to optimize these problems, because only one control cam a set of valves (intake or exhaust), a rocker arm valve is omitted, to simplify the valve between the camshaft transmission mechanism. In general, due to the small DOHC transmission member, into the high exhaust efficiency, is more suitable for a high speed when the engine power performance. For the pursuit of high-power Japan, European manufacturers, overhead camshaft design is certainly the most appropriate.
Such bottom-mounted camshaft engines are generally designed large displacement, low speed, high torque output pursuit, because the bottom-mounted camshafts is driven by the crankshaft to rely on, and then using a cam and rocker arm valve metal rods connected, a top camming rod, the rocker arm push rod to achieve opening and closing an engine valve, so that high speed ram pressure will be too large to break. However, with such a ram design, it has advantages of simple structure, high reliability, the engine restart the heart, and low cost. Because of the low engine speed torque performance is emphasized, the bottom-mounted camshaft is sufficient to meet this demand.
Since the two designs tend to differ, the former is the most for high-power, which is the pursuit of high torque. We know that the car fast speed, traction relies on strong torque, top speed is achieved on the power. There is also a simple formula: Power = speedX torque. When the naturally aspirated engine to enhance the power of the easiest way, is to increase the speed, the higher the speed or power naturally higher.
Why are the Americans love the bottom set camshaft?
developed in the automotive industry in Germany, the highway is not a lot of speed, speeding over 200 km of speed is a common thing, so naturally it is the power of their favorites. But Americans are not the same, their pursuit of highway cruising performance, not high engine speed. This situation has a great relationship with the United States, the United States vast land, and is mostly plain, straight road repair are straight, after World War II, Americans have been keen unique, large, luxury carts emphasis on comfort, these cars are usually the weight of large, hanging soft, straight-ahead driving comfort is very good, but the United States is very low oil prices, large displacement engines popular with people of all ages. So this engine is very high penetration rate of 6.0, 7.0 at every turn. Having said that, there is little need to add, we are often talking about engine power, and in order to determine the operating efficiency of the engine. But if there is a power density heard the term it? For this concept simply is released the same power, the smaller the volume of the engine, the power density is higher. Bottom-mounted camshaft of the engine due to its low to high torque, does not require as complicated overhead camshaft arranged as multi-valve cylinder DOHC, high strength top cover.
Therefore, the United States using bottom-mounted camshaft engine design is for the United States national needs, not the Americans will not make a good engine. But it also led to the US Department of the engine is not suitable for markets outside the United States, and therefore in the development of overseas markets, Americans need to develop more suitable for other markets engines.