Many people often only look at the maximum power, peak torque, and other book data when looking at a car's parameter list. They don't care much about what kind of technology the engine uses. When buying a car, it naturally favors high-power models. But sometimes, data can be deceptive. Before we get to the point, let's talk about the engine valve. The duty of the valve is to inject fuel air into the engine and remove the exhaust gas after combustion. In the current most common four-cylinder engine for domestic cars, the engine of most models has two intake valves and two exhaust valves independently per cylinder, four valves per cylinder, and the overall 16-valve engine is the most common on the market. The 16V that we often see on the hood means that this is a 16-valve engine. The multi-valve structure of the engine can make the combustion chamber more compact, the oil and gas mixing effect is good, the combustion is quick and full, and the speed of opening and closing is faster, thereby improving the working efficiency of the engine. After simply understanding the valve knowledge, we talk about the overhead camshaft. The vast majority of model engines are overhead camshafts. In theory, overhead camshafts are more suitable for the high engine speeds of modern engines. Compared with other forms, it has inherent advantages in reducing noise and vibration at high speed, and has high intake and exhaust efficiency and simple transmission mechanism. Therefore, the valve overhead and overhead camshaft is the most common form of valve mechanism. According to the number of camshafts, it is divided into a single overhead camshaft (SOHC Single Overhead Camshaft) and a DOHC Double Overhead Camshaft (DOHC Double Overhead Camshaft). When the intake and exhaust valves are arranged on a camshaft, the camshaft is used to control the opening and closing of the valve. This is a single overhead camshaft. When the intake valve and the exhaust valve are respectively controlled by two camshafts, this is called double overhead camshaft. On the surface, due to a single camshaft, the dual overhead camshaft structure is more complex, and it is technically more advanced than a single overhead camshaft. However, from this point of view, it is certain that bi-convexity is better than single-convexity. Not at all. First, the single overhead camshaft is inherently simpler than the double overhead camshaft mechanical mechanism. Since one camshaft opens the intake and exhaust valves, the valve opening time is fixed, and the intake air amount and the oil and gas mixture are affected little by other factors. This has caused SOHC to naturally have the advantage of low torsion and excellent performance, and when the normal city road is running at low speed, the low-speed torque responds quickly and is more suitable for the rhythm of starting and stopping. What's more, the displacement of ordinary domestic cars is generally lower than 2.0L. Under the condition of small displacement, it is important to drive a ton of vehicles with low torsion capacity. SOHC just fits this need. It can be said that using the same technology of SOHC and DOHC engines, the SOHC engine must be stronger than DOHC in its initial stage. The low torsion ability is good, and the advantage is that the fuel economy is better. These advantages are not possessed by DOHC. The dual overhead camshaft can control the opening and closing time of the intake and exhaust valves more freely, compensate for the inaccuracy of the single overhead camshaft opening and closing valve, and ensure more air than the single camshaft in the high speed region. The inputs and fuels are mixed, so SOHC and DOHC have a hard time in terms of output power. However, for domestic vehicles, there is little time for the engine to reach the high-speed range, and if a DOHC design is adopted for a generally small-displacement engine, the starting meat will be further amplified and the amount of fuel injected will need to be increased to compensate for low-speed oil and gas. The disadvantage of poor mixing is that the smaller the displacement is, the better the low-twist condition is with a double camshaft. Due to the inherent advantages of SOHC, the engine performance of a single camshaft is even better during normal car use. For example, the 1.8L self-priming engine carried by the eight generations of Dongben Civic (parameters, pictures, inquiry), Is a very good single camshaft engine, it has comparable to the fuel consumption of the 1.6L engine and the output of the race 2.0L engine, is a smooth engine that is very suitable for everyday use. Why do most of the models still use DOHC? The reason is that SOHC cannot freely control the intrinsic defects of valve opening and closing time that are difficult to overcome, and the DOHC engine can have various technologies such as continuously variable valves, variable intake, turbocharging, and supercharging to make up for the defects. And after the displacement exceeds 1.8L, the disadvantage of low twist is also weakened. In the high-speed, DOHC power reserve is thick, power failure is slow, speed is very high, performance is relatively strong, so DOHC is not unreasonable. Summary: Single overhead camshafts and dual overhead camshafts are only structurally different and they each have advantages and disadvantages. SOHC has a low twist output, simple structure, and easy maintenance; DOHC technology is more advanced, power output is smoother, noise and vibration are smaller, and speed is higher. Therefore, when buying a car, if it is mostly used for commuting in cities and towns, especially for small-displacement self-priming engines, the choice of SOHC is more appropriate. If long-distance running highways are used, it is recommended to choose DOHC. One-convex and double-convex are not absolute who is good and who is bad, apply to their own road conditions and driving habits, to get up more convenient.
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