Before we get to the intake manifold, let's think about how the air gets into the engine. In the introduction to the engine, we have mentioned the operation of the piston in the cylinder. When the engine is in the intake stroke, the piston moves down to create a vacuum in the cylinder (that is, the pressure decreases), so as to create a pressure difference with the outside air and allow air to enter the cylinder. For example, you've all had an injection, and you've seen how a nurse inhales medicine into a syringe. If the pail is the engine, then when the piston in the pail pulls out, the liquid will be sucked into the pail, and the engine draws air into the cylinder.
Due to the low temperature at the inlet end, the composite material has become a popular intake manifold material. Its light weight makes the inside smooth, which can effectively reduce the resistance and increase the intake efficiency.
Ok, back to the topic, and the engine intake manifold is located in the throttle, between the inlet valve is called "manifold", because the air into the throttle, after manifold buffer system, air flow in the "differences", corresponding to the number of engine cylinder if four-cylinder engine has four, five cylinder engine has five, the air into the cylinder, respectively. For the natural intake engine, because the intake manifold is located behind the throttle valve, when the engine throttle is small, the cylinder cannot absorb enough air, which will result in a high degree of manifold vacuum. And when the engine throttle is open, the vacuum in the intake manifold will be reduced. Therefore, the jet fuel supply engine will install a pressure gauge on the intake manifold to supply the ECU to determine the load of the engine and to give an appropriate amount of fuel injection.
Manifold vacuum can be used not only to provide pressure signals that determine engine load, but also for many other purposes. For example, the brake also needs to use the vacuum of the engine to assist, so when the engine is started, the brake pedal will be much lighter, because of the vacuum assist. Some forms of constant speed control also utilize manifold vacuum. And these vacuum tube once have leak or improper refit, can cause engine control maladjustment, also can affect brake actuation, so the reader is advised not to make improper refit on the vacuum tube as far as possible, in order to maintain the safety of driving.
The design of the intake manifold is also a matter of great learning. In order for each cylinder of the engine to burn equally, the length and curvature of the manifold of each cylinder should be as identical as possible. Because the engine is programmed to run on four strokes, each cylinder of the engine is pumped in pulse mode. As a rule of thumb, longer manifolds are suitable for low RPM runs, while shorter manifolds are suitable for high RPM runs. So some models will use variable length intake manifold, or continuous variable length intake manifold, so that the engine can play a better performance in each speed domain.
Article source: automobile encyclopedia net
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