As we all know, there are many forms of mechanical force received by electronic equipment. Among them, vibration and shock are the most harmful, and they cause about 80% of the failures. The main form of equipment damage is the resonance generated by a certain excitation frequency, exceeding the limit that the equipment can withstand. The in-vehicle electronic equipment is generally placed in the cabinet, mainly relying on the damping buffer of the cabinet damping system. At present, for the cabinets with a height of more than 1.2 meters, the installation method of the shock absorbers has been standardized, that is, four shock absorbers are installed at the bottom of the equipment, and two back frame type shock absorbers are installed on the upper part of the back.
Anti-resonance design and decoupling design are two major problems to be solved in the rack-mounted cabinet damping system. In order to prevent damage to the equipment caused by excessive resonance transmission rate of the damping system, in practical applications, we should preferentially use shock absorbers with low vibration transmission rate and low natural frequency to suppress the resonance of the cabinet. The center of gravity of the cabinet shock absorber is installed to avoid coupling vibration. However, in actual work, this installation method is difficult to achieve. In order to make the cabinet damping system have better damping effect, the vertical stiffness of the damping system is required to be approximately zero, and the horizontal stiffness is matched with the horizontal stiffness of the bottom damper.
At present, there are four types of vehicle cabinet dampers commonly used: E-type damper, wire rope shock absorber, harmonic-free damper, and rubber sandwich mounts
. The advantages and disadvantages are as follows:
a) E-type damper: It has small static deformation and convenient installation. It is more suitable for the installation of the cabin and the interior of the car, but the natural frequency is high (requires anti-resonance);
b) Wire rope shock absorber
: Its stiffness has a soft and non-linear characteristic, low transmission rate, can adapt to a variety of stress states, and is mainly suitable for wall installation;
c) No resonance peak damper: It has good vibration damping and isolation effect, no resonance amplification, long life, but the load must be within 20% of the rated load of the damper, otherwise the effect will be worse;
d) Rubber sandwich mounts: It has good impact resistance, but requires installation space.
The angular acceleration of the in-vehicle electronic equipment cabinet is relatively large, and the vibration of the bottom of the shock absorber is weak in the horizontal direction. The following principles should be followed when selecting the back shock absorber:
a)The vertical stiffness of the back frame damper should be approximately zero to maintain the vertical decoupling of the cabinet;
b) The horizontal stiffness should be symmetric about the static equilibrium position of the cabinet to eliminate the coupling resonance;
c)The back frame damper should match the stiffness damping characteristics of the bottom damper.
The general measures for damping and buffering are:
1. Install the damper. The damping and cushioning of electronic products relies mainly on the installation of shock absorbers. Currently in the electronics industry, standardized rubber-metal dampers and metal spring dampers are used;
2. Enhance the vibration and impact resistance of products and components.