Why does the engine need air intake?

Because the engine is told that oxygen will be injected into the air intake system when working, gasoline will burn, which will drive the piston to move and make the car move back and forth through the crankshaft.

Gas treatment system

When the engine is working, the driver controls the opening of the accelerator through the accelerator pedal, thus changing the air intake and controlling the operation of the engine. After the air entering the engine is filtered by the air cleaner to remove impurities such as dust, it flows through the air flowmeter, enters the power room along the throttle passage, and is distributed to each cylinder through the intake manifold; When the engine is idling, some air bypasses the throttle and enters the cylinder through the additional air valve or idling control valve.

Variable valve timing technology can be divided into two categories: variable valve timing and variable valve stroke.

First of all, let's talk about the valve train of an ordinary engine. Everyone knows that the valve is driven by the crankshaft of the engine through the camshaft, and the valve timing depends on the rotation angle of the camshaft. When the engine is running, we need to let more fresh air into the combustion chamber and exhaust the exhaust gas as much as possible. The best solution is to let the intake valve open ahead of time and the exhaust valve close later. In this way, between the intake stroke and the exhaust stroke, the intake valve and the exhaust valve will open at the same time, and this overlap of the intake valve and the exhaust valve is called the valve overlap angle. On an ordinary engine, the opening and closing time of the intake valve and the exhaust valve are fixed, and the valve overlap angle is also fixed, which is the best valve timing obtained according to experiments and cannot be changed during engine operation. However, the engine speed has an influence on the intake and exhaust flow in the cylinder and the combustion process. When the rotating speed is high, the intake flow rate is high and the inertia energy is large, so it is hoped that the intake valve will open earlier and close later, so that fresh gas can be smoothly filled into the cylinder and as much mixed gas or air as possible. On the contrary, when the engine speed is low, the intake air flow rate is low and the flow inertia energy is also small. If the intake valve is opened too early, because the piston is exhausting upwards at this time, it is easy to squeeze fresh air out of the cylinder, which makes the intake air less and the engine unstable. Therefore, there is no fixed valve overlap angle setting that can make the engine output perfect at high and low speeds. If there is no variable valve timing technology, the engine can only choose the best fixed valve overlap angle according to the needs of its matching model. For example, the engine of a racing car generally adopts a small valve overlap angle to facilitate the power output at high speed. However, ordinary civilian vehicles adopt a moderate valve superposition angle, taking into account both high-speed and low-speed power output, but they will lose a lot of power at low and high speeds. Variable valve timing technology solves this contradiction by realizing variable valve overlap angle through technical means.

For example, in the early 1990s, Honda introduced a variable valve timing-lift control mechanism, which can not only change the valve timing, but also change the valve movement law. It is the first valve control system in the world that can control the valve opening and closing time and lift at the same time. It is the well-known VTEC mechanism: in general, the valve group of each cylinder of the engine is driven by only one group of cams, while the engine of VTEC system has two groups of different valve driving cams, which can be automatically switched through the automatic control of the electronic control system. VTEC system ensures different requirements for valve timing and air intake at low speed and high speed, and makes the engine achieve a unified and excellent state of power, economy and low emission at any speed. It should be noted that the engine adopts variable valve timing technology, which has not any negative effects while obtaining the above benefits, in other words, it has not put forward higher requirements for the working intensity of the engine.

The design of VTEC seems to adopt two different camshafts, one for low speed and the other for high speed, but the difference of VTEC engine is that these two different camshafts are designed on one camshaft.

In the intake camshaft of Honda engine, in addition to the original pair of cams (main cam and auxiliary cam) and a pair of rocker arms (main rocker arm and auxiliary rocker arm) for controlling two valves, a higher middle cam and corresponding rocker arm (middle rocker arm) are added, and small pistons controlled by hydraulic pressure are installed in the three rocker arms.

When the engine is at low speed, the small piston is in the original position and the three rocker arms are separated. The main cam and the auxiliary cam push the main rocker arm and the auxiliary rocker arm respectively to control the opening and closing of the two intake valves, and the valve lift is small, just like an ordinary engine.

Although the middle cam also pushes the middle rocker arm, because the rocker arm is separated and the other two rocker arms are not controlled by it, it will not affect the opening and closing state of the valve. When the engine reaches a certain set high speed, the computer will instruct the solenoid valve to start the hydraulic system to push the small piston in the rocker arm, so that the three rocker arms are locked together and driven by the middle cam C. Because the middle cam is higher than other cams, the opening time of the intake valve is prolonged and the lift is also increased. When the engine speed decreases to a certain set low speed, the hydraulic pressure in the rocker arm also decreases, the piston returns to its original position under the action of the return spring, and the three rocker arms are separated.

The whole VTEC system is controlled by the engine electronic control unit (ECU). ECU receives and processes the parameters of engine sensors (including speed, intake pressure, vehicle speed, water temperature, etc. ), the corresponding control signal is output, and the hydraulic system of rocker piston is adjusted by solenoid valve, so that the engine is controlled by different cams under different speed conditions, thus affecting the opening and timing of intake valve.