VVT-i, VTEC, VVL, VVTL-i, etc. can be seen on most cars. The meaning of these numbers is - variable timing timing technology.
Variable gas distribution technology, from the broad category, including variable valve timing and variable valve stroke, some engines only match variable valve timing, such as Toyota's VVT-i engine; some engines only match Variable valve travel, such as Honda's VTEC; some engines match both variable valve timing and matched variable valve travel, such as Toyota's VVTL-i, Honda's i-VTEC.
First of all, let's talk about the general engine air distribution mechanism. Everyone knows that the valve is driven by the crankshaft of the engine through the camshaft. The valve timing of the valve depends on the rotation angle of the camshaft. When the engine is running, we need to let more fresh air enter the combustion chamber, so that the exhaust gas can be discharged out of the combustion chamber as much as possible. The best solution is to let the intake valve open in advance and let the exhaust valve be delayed. Thus, between the intake stroke and the exhaust stroke, the simultaneous opening of the intake and exhaust valves occurs, and the overlap between the intake and exhaust valves is referred to as the valve overlap angle. In the ordinary engine, the opening and closing time of the intake and exhaust valves is fixed, and the valve superposition angle is also fixed. It is the optimal timing of the valve according to the test, and it is during the engine running. Can't change. However, the engine speed is high, the intake flow, and the in-cylinder combustion process are influential. When the rotation speed is high, the intake air flow rate is high and the inertia energy is large. Therefore, it is desirable that the intake valve is opened earlier and closed later, so that fresh gas is smoothly charged into the cylinder, and as much as possible mixed air or air. Conversely, 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, since the piston is moving upward and upward, it is easy to squeeze the fresh air out of the cylinder, so that the intake air is instead Less, the engine is not working. Therefore, there is no fixed valve overlap angle setting that allows the engine to output perfectly at high and low speeds. Without variable valve timing technology, the engine can only be optimally fixed according to the needs of its matching models. Valve superposition angle. For example, racing car engines typically use smaller valve overlap angles to facilitate power output at high speeds. Ordinary civilian vehicles use moderate valve superposition angles, while taking into account the high-speed and low-speed power output, but will lose a lot of power at low speed and high speed. The variable valve timing technology solves this contradiction by means of technical means to realize the variable valve overlap angle.
For example, in the early 1990s, Honda Japan introduced a variable timing timing-lift control mechanism that can change the timing of valve timing and change the law of valve movement. It is the world's first to control valve opening and closing at the same time. Two different situations of valve control systems such as time and lift. Nowadays, everyone knows VTEC mechanism: the general engine engine cylinder group is driven by only one set of cams, while the VTEC system engine has medium and low speed and high speed with two different valve drive cams, and can be automatically controlled by electronic control system. Manipulate and perform automatic conversion. The VTEC system ensures the low phase and high speed of the engine in different phases of the gas distribution and the amount of intake air, so that the engine can achieve the uniformity and excellent state of power, economy and low emission at any rate. It should be noted that the engine adopts the variable valve timing technology to obtain the above benefits without any negative influence. In other words, there is no higher requirement for the working strength of the engine.
VTEC is designed to use two different camshafts, one for low speed and one for high speed, but the VTEC engine differs in that it is designed with two different camshafts in place. On a camshaft.
In addition to the original pair of cams (primary cam and secondary cam) and a pair of rocker arms (main rocker and secondary rocker) that control the two valves, the Honda engine intake camshaft adds a higher middle. The cam and the corresponding rocker arm (middle rocker arm), the three rocker arms are equipped with a small piston that is moved by hydraulic control.
When the engine is at low speed, the small piston is in the original position, the three rocker arms are separated, and the main cam and the secondary cam respectively push the main rocker arm and the secondary rocker arm to control the opening and closing of the two intake valves, and the valve lift amount is small, the situation is like ordinary engine.
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