When the natural frequency of the valve spring is the same as or is an integral multiple of the valve opening and closing period, the spring resonates. In the operation of the motorcycle engine, the resonance is extremely harmful. It not only increases the noise of the engine, but also makes the torsional shear stress of the valve spring exceed the normal value several times. The spring force of the spring generates large fluctuations, the valve There are gaps in the mechanism that will cause beating, which can cause abnormal valve movement, spring breakage, and even serious safety accidents. In order to avoid resonance, most of the current valve springs use high self-vibration frequency. Carrying the reliability of the proud spring work, the engine mostly adopts a valve two spring structure, that is, a valve has two springs inside and outside, the load is distributed according to the principle of equal strength, which greatly reduces the spring height, once a certain The spring breaks and does not immediately cause damage to other components, which can effectively reduce the sudden occurrence of safety accidents.
The valve spring should have sufficient rigidity to mean that the pressing force of the spring must be greater than the maximum inertial force instantaneously generated by the valve train, that is, the product of the mass of the valve train mechanism and the maximum motion acceleration. However, in the actual working process, due to the vibration of the system caused by the harmonics of the cam rising curve, the valve motion law is distorted, the valve spring is in a continuous vibration state, the amplitude changes with the increase of the rotational speed, and the cycle may occur. The amplitude of the amplitude of the amplitude, which greatly increases the instantaneous load of the spring. According to experience, the actual load of the spring is twice as large as the inertial force of the valve. Therefore, there should be a margin when designing the spring stiffness, especially for high-speed motorcycle engines. The basic dimensional parameters of the spring include the average diameter, wire diameter, pitch, effective number of turns, and total number of turns. According to the position of the valve when it is closed and fully opened, the pre-tightening height of the spring and the height at the maximum tension are determined, and then the load of the spring at the moment is calculated, which can be initially determined.
When the vibration of the valve spring is running at high speed, the valve is quickly opened, closed and then opened, and the valve spring also moves with its high frequency and density, but the springs are not dense or sparse at the same time, but The active end is first compressed or lengthened, that is, the spring formed generally requires that the natural vibration frequency of the valve spring is twice as high as the engine speed, so that the vibration of the spring can be effectively reduced. In addition, a variable pitch spring can be used. When the valve lift changes, the effective number of turns of the spring also changes, and the stiffness also changes sequentially, thereby changing the natural frequency of the spring and eliminating the condition for generating resonance. If the inner and outer double spring springs with different self-vibration frequencies are opposite to each other, the vibrations can be mutually damped during vibration to avoid resonance. In some engines, vibration damping measures such as an external damping plate are used to reduce vibration. Valve spring selection and strengthening process The material requirements of the valve spring are strict. Generally, it is made of Zhouba, Yin or Yin alloy spring steel wire, and is tempered by oil bath.
Hong spring steel wire has superior performance, mechanical strength has great advantages in all oil bath steel wire, and plasticity index and winding performance are not inferior, and has high fatigue resistance and good anti-relaxation performance. The material is greatly peeled off and polished by two times during rolling, which greatly improves the surface quality, and a spring with high stress is required to be suitable. In order to ensure the performance of the valve spring, it has sufficient fatigue strength. In actual production, soft nitriding is often used after shot peening, which can further improve the fatigue strength. In recent years, the composite treatment process and refining treatment of soft nitriding and reheating have been gradually applied to the production process, and have achieved good results in practice and have been widely used. In addition, considering that the oil used in the machine contains moisture, the outer surface of the spring should be oiled to avoid corrosion.
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