The role of an ambulance transporting patients or is severely disabled person, in order to avoid deterioration of illness or injury in the course of transportation, general requirements for smooth movement and high speed. Designed for this people a wide range of damping device, in order to minimize the suffering of patients, critically ill patients to save precious lives. Initially the patient closely tied with tape or a large balloon wrap the patient, the result will increase the suffering of the patients, but the scene has delayed the inflatable treatment time, was then proposed for an ambulance vehicle installation damping device, but because of the cost is too high to put into practice. In this paper, the two degrees of freedom vibration damping apparatus using a low rigidity obtain lower gas spring resonance frequency and vibration transmissibility. So that the damping effect to achieve the best, and its low cost, suitable for commercialization.

Device structure Introduction

As shown in Figure 1 is a schematic view of the structure of two degrees of freedom stretcher damping means, which is fixed to the lower end of the car floor, connected to the upper end of the stretcher, the stretcher between the vehicle floor and the installation of a connecting device, the control system mounted thereon, wherein two cylinders are connected through the throttle hole and airbags.

When the vehicle body vibration, gravity and patient stretcher with air pressure equilibrium.

When the vehicle body vibrates up and down, while two-cylinder gas is compressed, the pressure and the pressure inside the balloon inside the cylinder to produce a differential pressure, prompting the throttle orifice between the cylinder and the balloon has air flow and damping effect elastic joint action of the gas cylinder amplitude attenuation.

Pitching vibration occurs when the body, about the role of two different control systems, all the way to the cylinder pressure (such as pressure left), the other way on the contrary, when the left under pressure, cylinder pressure is greater than the pressure of the air bag, the air flow from the cylinder to airbag flow until the pressure is equal on both sides; and on the right is a balloon pressure is greater than the cylinder pressure, air flow into the cylinder from the air bag, the same is to achieve equal. By adjusting the electromagnetic valve to adapt the system of two different cross-sectional area of the throttling orifice, thereby generating two different damping to suit different road conditions. Throttle aperture area is larger, the greater the flow, the smaller the gas resistance, damping effect smaller. Proper control of the throttle aperture area so as to adjust the size of the damping force to achieve the best damping effect.

Gas Spring Vibration Analysis

Ambulance stretcher damping device having a damping effect to be true, it must ensure a substantially constant natural frequency, so as to by means of theoretical analysis targeted use of effective methods and to maintain a substantially constant natural frequency characteristic of the It depends on maintaining a constant air volume system, thus ensuring the ambulance stretcher with during normal working height. Here we use the simultaneous action of the cylinder and airbag.

Proper design and use of damping devices must clarify the characteristics of the applied load, which may be non-periodic cycles that can be sustained or transient, may be harmonic or random. Between the base and will be protected by damping vibration device is placed, it acts as a mechanical filter, the equivalent of a single degree of freedom damped spring. If the foundation is a sinusoidal oscillation, the device is protected sinusoidal response, but the amplitude reduced; if the underlying random vibration means is a rigid body be protected, which are resonant frequency response of the entire system as the main frequency with random harmonic vibration components to be protected if the device is an elastic body, it is a response bandwidth than random vibration excitation of vibration to narrow.

The device uses a gas damping shock absorber, its principle is to use the gas viscous damping between the gas molecules and the wall friction and vibration energy. And the use of the characteristics of the full Orifice damping adjustment to achieve the best damping effect. Using a gas damper biggest feature is the air of low stiffness, low coefficient of elasticity, and gave a lower than the resonance frequency 8Hz, but there are load and no-load natural frequency substantially the same, so simplifying the resonance damping device control. In general, the excitation frequency of the device is determined by the specific conditions of the project, it can only reduce the resonance frequency of the device from the start, that is, increase or decrease the quality of stiffness, but the actual project, the quality is generally not allowed to change, so in some of the features of each device to ensure that the premise should be possible to reduce the stiffness of the device.