Floating Clamping Mechanism of PT Fuel Injector and Its Dynamic Characteristics Analysis

PT fuel injector is one of the most important parts of modern diesel engine.To satisfy the requirements of the rapid and accurate test of PT fuel injector,the self-adaptive floating clamping mechanism was developed and used in the relevant bench.Its dynamic characteristics directly influence the test efficiency and accuracy.However,due to its special structure and complex oil pressure signal,related documents for evaluating dynamic characteristics of this mechanism are lack and some dynamic characteristics of this mechanism can＇t be extracted and recognized effectively by traditional methods.Aiming at the problem above-mentioned,a new method based on Hilbert-Huang transform（HHT） is presented.Firstly,combining with the actual working process,the dynamic liquid pressure signal of the mechanism is acquired.By analyzing the pressure fluctuation during the whole working process in time domain,oil leakage and hydraulic shock in the clamping chamber are discovered.Secondly,owing to the nonlinearity and nonstationarity of pressure signal,empirical mode decomposition is used,and the signal is decomposed and reconstructed into forced vibration,free vibration and noise.By analyzing forced vibration in the time domain,machining error and installation error of cam are revealed.Finally,free vibration component is analyzed in time-frequency domain with HHT,the traits of free vibration in the time-frequency domain are revealed.Compared with traditional methods,Hilbert spectrum has higher time-frequency resolutions and higher credibility.The improved mechanism based on the above analyses can guarantee the test accuracy of injector injection.This new method based on the analyses of the pressure signal and combined with HHT can provide scientific basis for evaluation,design improvement of the mechanism,and give references for dynamic characteristics analysis of the hydraulic system in the interrelated fields.

Design and experiment of a Chinese chive harvester

Recognizing the labor intensity of current domestic Chinese chive harvesting and the need for its mechanized harvesting,a self-propelled electric Chinese chive harvester is designed.The machine is composed of a control system,supporting mechanism,cutting parts,conveying and clamping mechanisms,frame,and collection system.It can complete Chinese chive feeding,cutting,transmission,and binning operations at one time.It has a cutting width of 0.25 m and wheelbases of 260 mm and 460 mm.Two 12 V,42 Ah lead-acid batteries were used in series as the power supply.The mechanical properties of Chinese chive were analyzed,and shear and compression tests were carried out to determine that the average value of the maximum shear force on the chives is 129 N.Up to a compressive force of 225 N,Chinese chives are not damaged.According to the physical characteristics of Chinese chives and the requirements of the harvesting operations,design and calculation of the key components of the harvester’s transmission mechanism and the strength of the whole machine frame were completed.An embedded control system and Cortex-M3 microprocessor were used to control the harvester and realize its functions of rolling and harvesting while regulating its speed and protecting its motor.Using the Box-Behnken test design method,the machine’s operating speed,cutter speed,and cutter height were selected as influencing factors,and the lodging rate and loss rate were evaluated as a test.A mathematical regression model of influencing factors and evaluation indexes was established to analyze the influence of these factors and indexes and optimize test parameters.The optimal parameter combination is determined to be:operating speed,1.1 km/h;cutter speed,220 r/min;cutter height 2.0 cm.The parameters were verified from field tests and the results showed that under the optimized parameter combination,the average lodging rate was 3.96% and the average loss rate was 3.23%,indicating that the Chinese chive harvester meets the agronomic requirements of Chinese chive harvesting.This harvester could be modified to harvest other crops such as chrysanthemums and Mongolian Chinese chive.