Release Date：2017-09-20 17:54:48 sentiment：0 source：admin
Camshaft is an important part of valve train of automobile engine. The structural design and processing quality of camshaft directly affect the performance of the engine . In recent years, due to the needs of environmental protection, fuel efficient and low-emission engines are under development. In order to realize the pollution discharge of automobile exhaust, and high speed, high output power of engine, many engines use the structure of many multi-valve ,gas phase, variable valve lift, which increases the load of valve spring. At the same time, in order to reduce the fuel consumption and the friction loss, the roller structure is adopted between cam and rocker arm, high pressure zone is formed in the contact surface of the cam and roller, which requires for a much higher demand on the stability, dynamic balance, wear resistance and anti torsion strength of camshaft movement. In addition, for the purpose of light-weight and low-cost automobile, we should make the parts as simple as possible, reduce the weight, use materials reasonably without affecting the performance of each part .
Generally, in a straight-line engine, a cam corresponds to a valve. V-type engines or horizontally opposed engines share one cam per two valves. While the rotor engine and valveless valve distribution engine do not need cam because of its special structure.
In order to produce lightweight, easy-processing and low-cost engine, and its high speed and high output power, the engine parts, especially the design of the camshaft must be reconsidered, it should bear higher contact pressure with compact structure, high degree of concentration and light weight . In current application of camshaft, cylinder lubrication system has been focused on the hollow camshaft, the fuel pump will achieve the GDI drive component on the camshaft, VVT (variable valve timing) is used in cam shaft end of the camshaft.
In the valve train, the performance requirements of each part of the camshaft are different. For cam and fuel pump driving wheels, wear resistance, adhesion resistance and pitting corrosion are required;
For shafts, good rigidity, bending and torsion performance is required.
With the development of lightweight, high-concentration and low-cost camshaft, the advantages of assembling camshafthave been gradually recognized and accepted.
The shafts and cams of the assembled camshaft are manufactured separately and then assembled together. Generally, the cam is made of carbon steel or powder metallurgy material, the shaft neck is made of powder metallurgy parts or the steel tube which is centered on the core shaft, and the mandrel uses the cold drawing seamless steel tube with thin wall. Carbon steel cam can be quenched with high frequency or carbonized , it has high adhesion resistance and pitting corrosion resistance.
In the design of the assembled camshaft ,we can make the cam width narrow, the interval small, the cam arrangement should be very compact. Compared with the traditional camshaft, the utility model has the advantages of light weight, low processing cost, reasonable material utilization, etc. And the weight is reduced by 45% compared with the solid shaft cam shaft.
The key technique of assembled camshaft is the connection method, which determines the manufacturing process and equipment because of the different connection methods. Assembled camshaft began in the 1980s and welded linked camshafts were the first ones to be developed . In the middle of the 1980s , sintered camshaft was put into use. At the same time, the camshaft produced by pipe expanding method appeared. In the late 1990s , knurling connecting camshaft was under development. With the advent of new connection methods, assembled camshaft manufacturing technology has also been updated constantly.
because of the thermal deformation, the dimensional accuracy of the camshaft decreases when the welding-connected camshaft is welded, and the thermal change is easy to cause cracks in the welding part, and the quality is difficult to guarantee; While the sintered connecting cam shaft is in the process of powder sintering forming cam , the cam is further connected with the steel tube in the liquid state, The process must be carried out in a sintering furnace above 1000 degrees centigrade. The shaft is easy to bend at high temperature, resulting in dimensional accuracy error, Moreover, when sintering, the performance of the material is limited, and large sintering furnace is needed, so the thermal efficiency is not high; The pipe- expanding method firstly matches the cam with the steel tube, then adds hydraulic from the inside of the tube or expands mechanically to bear the inner pressure of the expanding pipe, and the cam wall must be rather thick, At the same time, in order to make the expansion easier, the thin-wall steel pipe must be used. Because of the special requirements of high-pressure operation, the equipment should be large-scaling ; Although Hot and cold sleeve interference connection method is widely used in the production of machine parts, it is not suitable for camshaft production, Because in the cam and the shaft heat sleeve connection, the cam is heated and softened. It is difficult to guarantee the wear resistance during friction, During operation ,many cams conduct heat to the end of the shaft, so that the connection interference of initial work and the end changes, the connector can not be consistent; Knurling has some advantages in reliability, accuracy, equipment, energy consumption and so on.
Further development of composite camshafts will focus on developing materials and optimizing processing techniques. The use of composite materials, such as ceramic materials, is being vigorously developed in the market. Mahler is engaged in the development of modular camshaft extensions. For example, the integration of fuel pump starter and sensor components is also gaining favor. The synchronization of the inlet or outlet cam section of the SOHC camshaft can be achieved by Mahler's nested camshafts.
Assembled camshaft is developing at a high speed , it is mainly used in high-performance engines. With the development of assembled camshaft production technology, the assembled camshaft with better performance, lower cost and diversified technology cam will emerge.