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Camshaft working principle

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Camshaft working principle

Classification:
Company news
Release time:
2018/03/17 10:09
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[Abstract]:
The key to the camshaft is the cam. When the camshaft rotates, the cam opens/closes the intake and exhaust valves in time with the movement of the piston. Therefore, the shape of the cam has a direct

  The key to the camshaft is the cam. When the camshaft rotates, the cam opens/closes the intake and exhaust valves in time with the movement of the piston. Therefore, the shape of the cam has a direct relationship with the engine operating conditions at different speeds.

  To understand why, let's first imagine an engine that is operating at extremely slow speeds - 10 or 20 rpm - in which case the piston needs several seconds to complete one cycle. In reality, the normal operation of the engine can not be so slow, but we imagine it anyway. At such slow speeds, the cam shape we want is that the intake valve opens when the piston begins to move downwards into the intake stroke (referred to as top dead center, or TDC). When the piston is in the end, the intake valve closes. After the combustion stroke is over, the exhaust valve opens when the piston is at the bottom (referred to as bottom dead center or BDC) and closes at the end of the piston's exhaust stroke. As long as the engine has been operating at such a very slow speed, this good working condition will continue. However, what happens if the speed increases? Let's take a closer look. The construction of a well-operated camshaft with a rotational speed of 10-20 rpm is no longer suitable if the rotational speed increases. When the engine speed reaches 4000 rpm, the valve will open and close 2000 times per minute, that is 33 times per second. In this way, the piston moves very fast, so that the air/fuel mixture enters the cylinder very quickly.

  When the intake valve opens and the piston begins its intake stroke, the air/fuel mixture starts to accelerate in the intake flow duct and is ready to enter the cylinder. The air/fuel mixture will move at a very high speed when the piston is at the end of the intake stroke. If the intake valve is suddenly closed, all air/fuel mixture is blocked and cannot enter the cylinder. By extending the opening time of the intake valve, when the piston begins the compression stroke, the momentum of the high speed air/fuel mixture continues to force the mixture into the cylinder. Therefore, the faster the engine operates, the faster the air/fuel mixture moves and the longer we expect the intake valve to open. In the case of high speed, we also hope that the opening of the valve is larger. This parameter is called the valve lift and it is determined by the cam profile.

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