1、Automotive engine camshaftBrief introductionThe camshaft is a part of the piston engine. Its role is to control the opening and closing operation of the valve. Although the camshaft rotational speed in a four-stroke engine is a half of the crankshaft (the same as the camshaft rotational speed in a two-stroke engine with the crankshaft), but usually it is still very high speed, but also need to withstand the large torque, so the design right demanding camshaft in terms of strength and support mat
2、erial is generally a special cast iron, occasionally using forgings. Valve motion law related to engine power and operation characteristics, the design in the design process of the engine camshaft occupies a very important position.StructureThe main body of the camshaft is the same as the one with the cylinder length of the cylindrical rod. The above sets have several cam for driving the valve. One end of the camshaft camshaft bearing support and the other end is connected to the drive wheels.Ca
3、m side was egg-shaped. The design aims to ensure the the cylinder sufficient air intake and exhaust, specifically, within the shortest possible time to complete the valve opening and closing movements. In addition, taking into account the durability of the engine and the smoothness of operation, the valve can not be generated due to the deceleration process of opening and closing movements too much too large the impact of serious wear and tear of the valve, otherwise it will cause an increase in
4、 noise or other serious consequences. Therefore, the cam and the power of the engine torque output as well as the operation of the ride there is a direct relationship.Generally inline engine, a cam corresponding to a valve V-type engine or horizontal opposed type engine, every two valves share a cam. The rotary engine the valveless with gas engine because of its special structure, does not need to camPositionIn the long period of time, the bottom-mounted camshaft in an internal combustion engine
5、 is most common. Typically such engines, the valve is located in the top of the engine camshaft machine, i.e., so-called the OHV (Over Head Valve, OHV) engines. Usually camshaft located on the side of the crankcase, through the gas distribution agencies (such as tappet, push rod, rocker, etc.) valve control. Bottom-mounted camshaft general also called side-mounted camshaft. Far distance valve, and each cylinder is usually only two valves in such an engine camshaft, so the speed is usually slower
6、, ride comfort is poor, the output power is also relatively low. However, the engine output torque and low-speed performance of this structure is relatively good, relatively simple structure and easy maintenance.Now most of the production cars engine is equipped with overhead camshaft. The overhead camshafts structure closer to the camshaft valve, to reduce the kinetic energy of the waste caused by the bottom-mounted camshaft due to the larger distance between the camshaft and the valve shuttle.
7、 Overhead camshaft of the engine valve opening and closing action is relatively rapid, and hence higher speed, and the smooth running is also better. The engine of the the overhead camshafts structure appeared earlier the SOHC (Single Over Head Cam, overhead single camshaft) engine. This engine is only installed at the top of a camshaft, and therefore generally only two to three valves of each cylinder (the intake air a to two exhaust), the high-speed performance has been limited. Technology upd
8、ates DOHC (Double Over Head Cam, double overhead camshaft) engine, this engine with a two camshafts per cylinder can be installed four to five valves (intake two to three, Pai gas two), high-speed performance significantly improved, but at the same time the low-speed performance will be affected to some degree, the structure will be complicated and difficult to repair.ClassificationAccording to the the camshaft number of how many, can be divided into single overhead camshaft (SOHC) and double ov
9、erhead camshaft (DOHC), two kinds. The single overhead camshaft camshaft is only one camshaft, double overhead camshaft is two, this is too straightforward explanation.The single overhead camshaft with a camshaft in the cylinder head, direct drive into the exhaust valve, it has a simple structure, suitable for high-speed engine. Generally used in the past side camshaft, the camshaft in the cylinder side, is driven directly by a timing gear. The valve lifter to the rotation of the camshaft is converted into reciprocating motion of the valve must be used to transfer power. Thus, more parts of the reciprocating motion, the inertial mass, is not conducive to high-speed movement of the engine. Moreover, the slender tappet has a certain degree of flexibility, prone to vibration, accelerated component wear, even the valve control is lost.DOHC cylinder head equipped with two camshafts, one is used to drive the intake valve, the other for driving the exhaust valve. Do
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