Study Of Peak-shaving Performance Of Variable Gap Magnetorheological Buffer

Vehicle crash accidents occur frequently,among which the frequency of frontal crash is high and the peak force generated is more harmful to human beings,thus reducing the peak force is crucial for the protection of the lives of drivers and passengers.The crash box is the main energy-absorbing cushioning structure in a car bumper,and most of the traditional crash boxes have been optimized in terms of material and structure,and have achieved some achievements,but there is still a deficiency of poor self-adaptation.Magnetorheological(MR)buffers,with their fast and adjustable damping characteristics,have been widely researched in the field of vibration damping and isolation,providing a new idea for weakening peak forces in impact applications.MR buffers are usually constructed with equal-gap damped runners and rely on excitation current control methods to weaken peak forces,which are extremely challenging in terms of reliability under the very short duration of high-speed shock loads.Based on this method,a MR cement buffer with a cone section of the cylinder tube is proposed.The damping gap is gradually reduced with increasing piston displacement.In the decaying stage,the buffer force decay is suppressed by decreasing the gap width to hinder the flow rate reduction and increasing the magnetic induction strength.The study of the variable gap MR buffer is based on a combination of theory,simulation and experimentation,and is based on mechanical modeling,buffer design,test verification and evaluation of peak-shaving.The specific work is as follows:(1)Firstly,the characteristics of several flow channel forms are compared and analyzed and Type III is selected as the damping channel form;then the mechanical model of the MR buffer is analyzed based on the HB model,the spring force and gas pressure are calculated,and the damping force in the flow mode and shear mode in the micro-element flow channel is analyzed using differential ideas;then the effect of local losses in the flow channel on the pressure drop is detailed,and a mechanical model for MR cement buffer considering the minor losses is established,which is called HBM model,followed by an analysis of the total buffer force based on this model.Finally,the parametric design of the variable gap MR buffer is divided into three parts: the flow channel size design,the magnetic path design and the dynamics verification.(2)The impact test of the variable gap MR buffer was carried out and the test results were analyzed.A drop hammer impact test platform was built,a physical prototype of the variable gap MR buffer was made,and then the impact test conditions were determined;the flow channel analysis of the variable gap MR buffer was carried out,the impact test results were analyzed in detail,the HBM model was compared with the test results,and the accuracy of the model was further verified by the peak force and dynamic range.The HBM was finally found to be a good predictor of the dynamic behavior of the variable gap magnetic rheological buffer.(3)In order to evaluate the peak-shaving performance of the variable gap buffer,the theoretical buffer force-displacement characteristic curves of the two types of buffers were studied and four quantifiable evaluation indexes were proposed: peak force difference,plateau angle,compression force efficiency and dynamic range.The peak-shaving capability of the variable gap buffer was analyzed in detail by the four peak-shaving evaluation indexes respectively,and it was finally found that the variable gap buffer can achieve excellent peak-shaving performance compared with the equal gap buffer.The final finding was that the variable gap buffer showed excellent peak-shaving performance with a slow rise and a smooth fall in buffer force compared to the equal gap buffer.