Analysis of the technical operation principle inside the car engine

The engine is the heart of the car. Every place where work is done is like an atrium or ventricle. Let me tell you, there are several "variable" technologies in these atria and ventricles. According to the different driving conditions of the car, the engine will be changed accordingly to make it more powerful.

Variable compression ratio

The so-called compression ratio is the ratio of the volume of the cylinder when the piston is at the bottom dead center to the volume of the cylinder when the piston is at the top dead center. There are currently two ways of variable compression ratio on the market. One is a dual-cycle technology similar to the Atkinson-Otto dual cycle. This technology is relatively simple. It changes the degree of compression of the gas in the cylinder by delaying the intake valve during the compression stroke. Its engine expansion ratio remains unchanged.

Another method is to change the physical structure of the engine, by changing the stroke of the piston to change the compression ratio. Saab also tried this method in the past, but this technology was quite difficult to use. Until the day of its bankruptcy, no one thought of a way to mass-produce Saab's SVC engine. Currently, the only engine that truly mass-produces this technology is Infiniti's VC-T 2.0T engine. The compression ratio of this VC-T engine can be freely adjusted in the range of 8:1-14:1. Its main core engine has a set of multi-link crank-connecting rod mechanisms with a special structure.

Perhaps many people will ask, what are the benefits of variable compression ratio? Let's put it this way, the compression ratio determines the pressure of the gasoline engine compression mixer, and the characteristics of gasoline combustion also determine that the pressure of the mixture in the cylinder cannot be too high. Especially in supercharged engines, if you want to save fuel, you have to have a high compression ratio. If you want strong performance, the compression ratio cannot be too high, otherwise there will be very low combustion efficiency, detonation and other problems. If there is such a variable compression ratio, it will be different. When the engine is under low load, it can use a high compression ratio to ensure fuel economy; when the engine is under high load, it can provide you with a low compression ratio to ensure higher power output.

Variable cylinder

Variable cylinder is what we call cylinder deactivation technology in daily life. From its name, we can guess that it is to stop some cylinders from working. In fact, this technology is not very advanced . It was invented by General Motors a long time ago. Its L62 V8 engine can be transformed from an 8-cylinder engine to a 6-cylinder or 4-cylinder engine. The specific principle of this technology is to hold up the intake and exhaust valves of the cylinders that need to be closed, so that they stop intake and exhaust, and stop fuel injection and ignition at the same time. As for how to implement these technologies? I won’t say more here. Every car company has different ways, and it may take several days and nights to explain in detail. What we want to understand is, what is the benefit of this cylinder deactivation technology?

In fact, this technology is quite good for large-displacement engines. After all, in situations such as traffic jams on urban roads, the power of large-displacement cars will be useless, and fuel consumption will also be lost in vain. Seeing this, some readers may ask, if the engine shuts down half of the cylinders, can half of the fuel be saved? The answer is no. After shutting down the cylinder, the piston will not be disconnected from the crankshaft. At this time, the working cylinder must also undertake the movement of the piston that has been shut down. And after shutting down the cylinder, the smoothness of the engine will be affected a little bit. However, at present, the editor is more looking forward to Ford's 1.0T three-cylinder engine's cylinder deactivation technology!

Variable valve

Variable valve technology is now relatively mature, especially variable valve timing and variable valve lift. Variable valve timing represents the time when the valve is open, and variable valve lift represents the size of the valve opening. Although different manufacturers have different names for variable valve timing technology, the implementation methods are similar. Its specific working principle is that the ECU coordinates and controls, and the sensors in various parts of the engine report the operating conditions to the ECU in real time. The timing mechanism is adjusted to change the opening and closing time of the valve, or advance, lag, or remain unchanged.

Relatively speaking, variable valve lift technology is more difficult. Each manufacturer has different design concepts and methods for this technology. The most representative ones are Honda iV TE C, Audi AVS, BMW Valvetronic, Infiniti VVEL, Fiat Multiair , and Mahle CIC. This technology can make appropriate valve lift at different engine speeds, allowing the engine to provide sufficient torque at low speeds and strong power output at high speeds.

Variable intake manifold

Similarly, there is a technology that can provide sufficient torque when the engine is running at low speed and strong power output at high speed. It is a variable intake manifold. As the name suggests, it improves the flow of air by changing the length of the intake manifold or changing the cross-sectional area. You may find it easier to understand how to change the length of the intake manifold. For example, a rotor is designed in the middle of the BMW intake mechanism to control the length of the intake manifold. By changing the rotor angle, the length of the intake airflow entering the cylinder can be continuously variable.

The so-called change of cross-sectional area is to use the physical principle that the larger the cross-sectional area of ​​the pipe, the smaller the fluid pressure; the smaller the cross-sectional area of ​​the pipe, the greater the fluid pressure. Very vague? Have you ever played with tap water when you were a child? If you pinch the front end of the water pipe, the pressure of the tap water will increase. So according to this principle, the manufacturer has developed such a mechanism. Taking the 4-valve engine as an example, the 2-inlet 2-outlet design, one of the intake pipes has an air valve, and this air valve is directly controlled by the ECU. At low speed, only one of the two intake valves is opened, which is equivalent to reducing the cross-sectional area by half. Similarly, at high speed, the ECU will command the valve to open, and the two intakes work at the same time, which is equivalent to increasing the cross-sectional area. There are also some dual-channel variable intake manifolds, main and auxiliary channel variable intake manifolds, stepless variable intake manifolds, etc.