The camshaft is an important part of the engine air distribution mechanism. In order to ensure that the engine work can be timely inhalation of fresh air, and timely discharge of the exhaust gas, the camshaft is responsible for driving the valve on and off on time, some camshaft also has the function of driving the distributor rotation. The speed of the car engine is very high, in order to ensure the efficiency of intake and exhaust, the valve with overhead design, the camshaft through the hydraulic tappet and other institutions to drive the valve action.
Although the speed of the camshaft is half the speed of the crankshaft in a four-stroke engine, its speed is still high and requires a lot of torque, so the requirements for the strength and reliability of the camshaft are high. The main body of the camshaft is a cylinder with the same length as the cylinder block. There are a number of cams. The material of the camshaft is usually special cast iron, sometimes made of forged and alloy. Most of the interior of the camshaft is made into a hollow structure, which not only reduces the quality of the camshaft, but also improves the ability of the cam bearing to be loaded. The camshaft is also machined with a lubricating oil passage, which is lubricated by the camshaft, rocker shaft, and rocker arm. Figure 1 shows the camshaft used by the Mitsubishi 4G63 DOHC engine.
The function is to detect the position and corner of the camshaft to determine the position of the top dead center of the compression stroke of the engine 1 cylinder. At start-up, the engine ECU recognizes the position and stroke of the cylinder piston, controls the fuel injection sequence and the ignition sequence based on the signals provided by the camshaft position sensor and the crankshaft position sensor, and performs accurate fuel injection and ignition control.
When the camshaft position sensor signal is interrupted, the control unit receives the crankshaft position signal can only identify a certain crankshaft corner to reach the top dead center of the cylinder, but I do not know which of the 1,4 cylinder is the compression stroke Only point. The control unit can still be fueled, but is changed from sequential injection to simultaneous injection. The control unit can still ignite, but the ignition timing is postponed to an absolute non-knocking safety angle. At this time the engine power and torque will be reduced, driving the feeling is to accelerate bad, fail to achieve the maximum speed, fuel consumption increased, idle instability.