Engine fuel consumption can be explained by the movement of a door. The size and length of time the door is opened determine the flow of people entering and leaving. The greater the opening angle of the door, the longer the opening time, the greater the flow of people entering and exiting, the smaller the opening angle of the door, and the shorter the opening time, the less the flow of people entering and exiting. When entering the theater to watch a show, one by one, the audience must check the ticket and the opening angle of the gate must be controlled. Some box roads are also equipped with railings, just like subway entrances and exits. To evacuate the audience as soon as possible when the theater is over, it is necessary to remove the box road railing and open the gate completely. The door opening angle and time determine the flow of people, which is very easy to understand.The same principle is applied to the engine, it producesValveThe concept of lift and timing. The valve lift is like the angle of door opening, and the timing is like the time of door opening. From the perspective of three-dimensional thinking, the angle plus the time is the size of a volumetric space, and its size determines the fuel consumption.
In actual operation,carThe operating load cannot be set in stone. With the difference in road surface, speed and throttle control, the engine load is always in a constantly changing state. This changing load affects the fuel consumption of the engine. When the load is large, the fuel consumption is large, and vice versa.The fuel consumption of a general car engine is determined byThrottleControl, it is like a door, through the throttle opening angle and time to control the mixing ratio. In the fuel electronic injection system, the air flow into the cylinder is controlled by the throttle, which is controlled by the accelerator pedal.The greater the throttle opening, the greater the air flow, and the electronic control unit (ECU) according to the throttle positionsensorAnd other locationssensorThe feedback signal is used to control the fuel injection volume of the fuel injector.
However, as engine valves increase andRotating speedIf the engine's valve lift and timing do not change, there will be conflicts that are difficult to solve under some working conditions, such as how to ensure the torque output at low speeds and the power output at high speeds, and the performance under these conditions. Fuel consumption and other issues cannot be completely solved with a fuel supply method controlled by a single throttle. The best way is to adopt a variety of variable forms of "comprehensive management", so there are variable intake pipes, variable compression ratios and variable valve lift and timing to solve this problem. Among them, the variable valve lift The process and timing, also known as the variable valve drive mechanism, is a common new technology in automobiles. In order to make the car fuel efficient, the designer did everything possible to make a fuss about the two key points of valve lift and timing.
The valve lift and timing are related to each other but they are two things. Lift is a problem of valve opening, which refers to how large the gap is when the valve is opened; timing is a problem of the time when the valve is opened and closed, and it refers to the time when the valve is opened and closed. They all determine the size of the intake air volume, but the valve timing involves the "overlapping phase" in the valve valve phase, that is, the "overlapping phase" where the intake and exhaust valves are opened at the same time (see this column "Valve Variable drive mechanism"), this will appear in any stage of the working condition. Variable valve timing is to control the valve intake time linearly from short to long according to changes in load, so that the engine's power output is smooth and smooth, and fuel consumption is reduced.
From a formal point of view, variable valve lift and timing systems have multiple operating modes. For example, Honda’s “i-VTEC” system and Toyota’s “VVT-i” system are both variable valve lift and timing systems (this Both devices are introduced in this column). There is also a way of "stop valve" (valve stop working), which is to stop part of the valve work according to the engine load condition. For example, the "H-VTEC" device in Honda engine has two intake and exhaust valves in each of the four valves in each cylinder, and each of them has one intake and exhaust valve that stops working at low and medium speeds and becomes two valves. Engine; while all 4 valves work at high speeds, the system controls the movement of the valves by adjusting the hydraulic pressure in the hydraulic valve lifters.
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