With the development of China's military industry and automobile industry, people pay more attention to the development of military vehicle electronic equipment. In the process of moving, military vehicles bear many kinds of mechanical forces, such as the more complex road conditions in the process of engine operation and transportation, which are affected by vibration and impact, and do great harm to the vehicle electronic equipment. According to the survey, the failure rate of electronic equipment caused by vibration accounts for more than 80% of the total failure rate of electronic equipment. Such a high proportion indicates that the vibration is the most harmful to the on-board electronic equipment, which must be paid attention to. Through the analysis of the working environment of the on-board electronic equipment, this paper designs the vibration isolation system of the on-board electronic equipment, hoping to make a positive contribution to the safety, reliability and development of the on-board electronic equipment in China.
1. Design of vibration isolation system for onboard and airborne electronic equipment
Because of the mechanical force from all aspects, the onboard electronic equipment has great harm to itself. The damage mode is mainly because the equipment produces resonance with large amplitude under a certain excitation frequency, which will eventually lead to damage because the vibration acceleration exceeds the limit acceleration that the equipment can bear, and directly lead to damage of on-board electronic equipment. Therefore, in the design of the vibration isolation system of the on-board electronic equipment, it is necessary to fully consider that the response value of the on-board electronic equipment under each excitation frequency is less than the limit that the equipment can bear, and protect the electronic equipment in the maximum sense, so as to make it more safe and reliable.

2 design principle of vibration isolator for vehicle electronic equipment
Generally speaking, the design of vibration isolation system for on-board electronic equipment is to achieve vibration reduction by adding vibration isolators to on-board electronic equipment. The electronic equipment and vibration isolator are regarded as a system. When the vibration signal and frequency are transmitted from the vehicle body, the vibration signal is weakened by the action of the vibration damper first, and then transmitted to the vehicle electronic equipment. In this way, the vibration signal and vibration frequency transmitted to the electronic equipment will be reduced by the action of the vibration damper, so as to achieve the purpose of protecting the electronic equipment. Adding shock absorbers to electronic equipment is not only a protection for the performance and safety of on-board electronic equipment, but also a protection for the performance and safety of the vehicle, which can improve the safety and comfort of the vehicle. By reducing the vibration signal and frequency, the vehicle body can be protected from vibration, so that the safety and reliability of the vehicle can be guaranteed.
Vibration isolation is to isolate or reduce the mechanical vibration transmission between them and the outside by installing vibration damping devices on equipment or devices. In order to reduce the impact of foundation vibration on electronic equipment and make electronic equipment work normally or not damaged, the elastic support, namely vibration damper, is installed between electronic equipment and foundation. This kind of isolation measures for electronic equipment is called passive vibration isolation. Generally, the vibration isolation of instruments and precision equipment is passive vibration isolation.
Passive vibration isolation coefficient: the vibration comes from the foundation, and its motion is expressed by u = uosin (ω T), which is also periodic vibration. Passive vibration isolation can also be represented by isolation coefficient η, which means the ratio of isolated object amplitude to foundation amplitude (or the ratio of vibration speed amplitude to acceleration amplitude), which can be calculated by the following formula:
ETA =xo/Uo
={[1+4ξ2（f/fo）2]/[1-（f/fo）2]2+4ξ2（f/fo）2}0.5
(1)
(1) Where XO -- vertical amplitude of the object (m);
Uo -- vertical amplitude of Foundation (m);
F -- frequency of vibration force (Hz);
Fo -- natural frequency of vibration isolation system (Hz);
K -- rigidity of vibration isolator (n / M);
M - mass of the object (kg);
G -- acceleration of gravity (9.8m / S2);
ξ - damping ratio of damper (damping ratio of rubber damper is 0.02-0.15). It can be seen from the expression of η that the isolation coefficient η is related to the frequency ratio (F / FO) and damping ratio ξ.
When f/fo
When f / fo = 1, the vibration isolation coefficient η is the maximum, and the vibration force is amplified. At this time, the system is in resonance state; the η value decreases with the increase of ξ. Therefore, for the equipment with frequent start and stop, in order to prevent the equipment from excessive resonance when passing through the resonance area during start-up or shutdown, the damper with larger damping should be selected.
When f / fo = 2, the isolation coefficient η = 1, and the vibration force is transmitted equally, the system has no isolation effect;
When f / fo > 2, the isolation coefficient η
Therefore, in order to make the vibration isolation system effective, it is necessary to make η 2. In the vibration reduction design of electronic equipment, the frequency ratio f / FO is generally 2.5-4.5, that is to say, in order to obtain satisfactory vibration isolation effect, the natural frequency of the vibration isolation support system should be 1 / 2.5-1 / 4.5 of the vibration dynamic frequency.
3. Design process of vibration isolator for vehicle electronic equipment
3.1 design preparation stage
In the design preparation stage of the shock absorber of the on-board electronic equipment, first of all, it is necessary to understand the working data of the on-board electronic equipment, the detailed information of the vehicle and the vibration isolator, and know the combination relationship between the parts, so as to ensure the overall grasp of the working environment, working state and performance of the shock absorber to be designed.
(1) Fully grasp the external structure of vehicle electronic equipment in a strict sense, and understand the installation drawings and installation dimensions. Have an overall understanding of the quality, center of gravity and performance of on-board electronic equipment, understand the location and number of supporting points of on-board electronic equipment, have an overall layout and planning for the installation of shock absorbers, and fully understand the working environment and working status of on-board electronic equipment.
(2) Have an overall grasp of the use and working environment of electronic equipment, understand the working temperature limit of the equipment, the requirements for humidity, oil pollution, solar radiation, etc. It is also necessary to know the direction, frequency, actual working condition, displacement and amplitude acceleration of the vibration of the on-board electronic equipment, and the generation and propagation of each frequency value.

(3) Understand the working environment of the vibration isolator, determine the size of the vibration isolator according to the size and installation position of the onboard electronic equipment, and ensure the installation and use of the vibration isolator in a scientific and reasonable way. Have an overall understanding and grasp of the static stiffness and dynamic performance of the vibration isolator. For example, the relationship with temperature, frequency, load and other changes. Have a full understanding of the service life of the vibration isolator, including the fatigue limit, etc. in the specific work, know the service conditions of the on-board electronic equipment, and should be equipped with the standard conditions and grade indicators of the electronic equipment. In the appropriate vibration isolation system, select the appropriate vibration isolator, for the protection of on-board electronic equipment to achieve a standard reasonable range.
3.2 specific methods and steps of design
In the design process of the vibration isolator of the vehicle electronic equipment, the design of the vibration isolation system is quite complex, considering the situation that the vibration isolation of the system must be considered comprehensively, especially the situation including the coupling vibration. The vibration isolation system of on-board electronic equipment is a vibration isolation system with six degrees, that is, translation vibration along three coordinate axes and rotation vibration around three coordinate axes. Through this kind of vibration amplitude and vibration signal, the vibration isolator should be fully tested to meet the comprehensive vibration reduction requirements in many cases.
3.2.1 design of reasonable support layout of electronic equipment vibration isolator
The installation position and the best supporting point of the vibration isolator of the vehicle borne electronic equipment are fully demonstrated to ensure that the equipment will not be bent and deformed under the dynamic and static load conditions, and the arrangement spacing of the vibration isolator is not easy to be too large with the electronic equipment, and it should be closely contacted with the vehicle borne electronic equipment, so as to fully play the role of the vibration damper and reduce the vibration of the electronic equipment to the maximum Small. At the same time, considering the load difference between the mounting points of the shock absorbers, when selecting the shock absorbers, it is necessary to select the same type of shock absorbers with different stiffness to meet the shock absorption requirements of the vehicle electronic equipment.
At the same time, we should avoid the arrangement of coupling in the installation mode of shock absorber, and choose the arrangement mode of shock absorber as the center of gravity plane of electronic equipment. When the configuration is symmetrical in the plane of xoz and YOZ, the vibration damping system of electronic equipment will move along the z-axis, that is, the coupling motion. When this happens, the decoupling can be realized by changing the stiffness layout. When the distance between the two fulcrums is too small, the coupling motion of a, C or B, C can be weakened to improve the stability of vehicle electronic equipment in driving. In order to obtain ideal damping effect, 2.5-4.5 should be used in the process of damping design. In the process of system design, the excitation frequency should be kept away from.

3.2.2 load design of vibration isolator for electronic equipment
When selecting the vibration isolator for on-board electronic equipment, first of all, we should have a comprehensive and full understanding of the working state of on-board electronic equipment, and study and demonstrate the requirements to be met to ensure that the use of the vibration isolator can solve the vibration problem of on-board electronic equipment. Secondly, the rated load of the isolator should be greater than the mass of the electronic equipment. Generally, the proportion is between 5% and 10%. Thirdly, the layout of the isolator should be scientific and reasonable, so that the stiffness of the isolator is symmetrical with respect to the plane of the mass center of the equipment. And the electronic equipment in the normal use of the vehicle, mainly from the vertical vibration, so the load-carrying capacity and layout of the vibration isolator of the vehicle electronic equipment mainly from the vertical vibration isolation and buffer.
First of all, the load of electronic equipment shall be comprehensively analyzed, and the vibration of electronic equipment shock absorber shall be tested under the maximum vibration, and its working performance shall be reasonably analyzed, so as to accumulate experience for the load design of shock absorber, constantly make the shock absorber test under the real situation, check its performance in the real situation, make it meet the actual requirements, and meet the vehicle mounted requirements The actual needs of electronic equipment.