Cison releases the OHV engine model in Stirlingkit.com now. Some people might wondering which version is better? flathead engines or OHV engines? actually it's about the problem Who's the winner, flathead, OHV or OHC engine?
If you look at the development history of the valve position, the position of the valve can be said to have changed a lot. In the era before World War II, the flathead configuration valve structure was the mainstream.
Why Flathead engines was Killed 65 Years ago?
The Flathead engine uses a now-extinct layout. Compared with the design of modern engines that arrange the intake and exhaust valves directly above the piston, the flathead arranges the intake and exhaust valves on the side of the piston. So flathead is also called L-head. In a nutshell, the valve is placed on the cylinder wall, and the intake and exhaust share a valve. This structure is simple and convenient, and even if the inlet and outlet valves arranged on the side are damaged, they will not hit the inside of the cylinder and cause a series of chain damage. More importantly, the cost is low. Therefore, in the age of immature metallurgical technology, it has become the choice of mature engines. It can also provide great response at low speeds, which is also valued by many people. However, the inherent defects of poor thermal efficiency lead to being gradually eliminated from the market. The L-shaped combustion chamber makes the fuel combustion efficiency very poor, and the final output horsepower is relatively low. After the casting technology matured, it was gradually replaced by the layout arranged on the cylinder.
What's OHC & OHV Engine?
However, most vehicles are designed for street use. In order to take into account the performance of low speed and high speed, multi-valve design (more than two valves per cylinder) has gradually become the mainstream. Each cylinder is equipped with at least four valves, two in and two out, and there are even high-performance civilian engines equipped with five valves or more reliable three-valve structure engines for off-road use. For these multi-valve engines, most of them belong to the OHC structure. OHC is the abbreviation of overhead camshaft, which is the overhead camshaft. The overhead camshaft and overhead valve can better cooperate with each other, and finally take into account the use of high speed and low speed.
Let me first tell you what OHV and OHC are. It is very likely that some people don’t know that OHV is a bottom camshaft, and OHC is an overhead camshaft. The formulation in the United States is usually OHV, and the design scheme of OHC is common in Japan or Europe. Next, I will give you the characteristics of the OHC engine.
What's the Character of OHC and OHV Engines?
Before answering the question, let’s briefly understand their own structures and characteristics technically:
Engines with OHV bottom camshaft designs generally have high horsepower, low speed, and high torque output. Because the bottom camshaft is driven by the crankshaft, then the camshaft and the valve lever use one Metal rods are connected, the camshaft lifts the crankshaft, and the crankshaft promotes the crank arm to complete the opening and closing of the engine valves. Therefore, an excessively high speed ratio will cause the small chain to withstand excessive pressure and even break. However, this design with a small chain also has its advantages, such as simple structure, high stability, center of gravity, and low cost. Because the engine speed is low, the emphasis is on torque performance, so the design of the bottom camshaft is very suitable for this requirement.
OHC (Overhead Camshaft) has undergone a development trend and is now divided into SOHC (Single Overhead Camshaft) and DOHC (Double Radial Camshaft). The single overhead camshaft is to use a camshaft to adjust the opening and closing of the intake and exhaust valves. Generally speaking, the single top is a design that matches the two-valve engine, because the efficiency of the two-valve engine in the intake and exhaust is lower than that of the multi-valve, and the layout of the valve angle is limited. The dual-diameter camshaft can solve this problem, because a camshaft only controls one set of valves (intake valve or exhaust valve), thus ignoring the crank arm of the valve, simplifying the distance between the camshaft and the valve. transmission mechanism. In general, due to the fewer components of the transmission system and the high efficiency of the intake and exhaust pipes, the dual radial camshaft is more suitable for the energy performance of the engine when it is fast. For Japanese and European manufacturers who pursue high power, the camshaft overhead design is the best.
What's the Difference between OHC and OHV?
Since these two designs have different emphasis, the former one is for high torque, while the latter one is for maximum power. We know that the fast acceleration and strong driving force of the vehicle depend on the torque, and the maximum speed is achieved by the output power. There is also a simple formula calculation here: output power = speed ratio X torque. The very simple way to increase the output power of the engine during self-priming is to increase the speed ratio. The higher the speed ratio is, the higher the output power will be. Why do only Americans prefer bottom camshafts? In France, where the automobile industry is relatively developed, many highways have no speed limit, and it is common to gallop at a speed of more than 200 kilometers. Therefore, of course, they like the ones with high power . But the Americans are different. What they pursue is the performance of constant speed cruise, and the engine does not need a high speed ratio. This has a lot to do with the basic national conditions of the United States. The United States is rich in products, and most of them are plain areas. The roads are all straight and straight. After World War II, Americans have always been keen on distinctive design, spaciousness, and comfort. This kind of luxury truck is generally heavy, with soft suspension, good straight-line driving comfort, and the price of oil in the United States is very low, and the high-horsepower engine is very popular among the masses. Therefore, the engine coverage of this type of dynamic rules 6.0 and 7.0 is very high. Speaking of this, there is one thing that must be added. We often discuss the fuel consumption rate of the engine, and use this to judge the efficiency of the engine. But haven’t you read the term power? For this definition, it simply means that the same output power is released. The smaller the engine, the higher the power. The bottom camshaft engine is attributed to its low rotation and high torque, and does not need the multi-valve, double camshaft, and high-toughness cylinder head cover with complicated layout like the overhead camshaft.
The OHV bottom camshaft used by American vehicles is for American highways. Considering its own situation, if it wants to expand to a broader foreign market, it must develop more suitable engine types.
The disadvantage of the DOHC engine is that it needs a timing belt or chain with a tensioner and other related parts. The timing belt or chain must be replaced regularly in later use, and the maintenance cost is high. Another disadvantage is larger size, more complex design, high engine manufacturing cost, such as V6 or V8 engine requires 4 camshafts, and higher center of gravity than OHV engine.
The OHV engine has small cylinder block, long life and high torque, so many refitting enthusiasts have transplanted V8 engines in their cars, while the DOHC high-speed and high-power features are obviously more popular today when small displacement is in power.
3 types of each engine has its own pros and cons. Who do you think is better between OHV and DOHC and flathead? Welcome to discuss.
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