Analysis and Experimental Investigation of Vibration Characteristics of Rotary Platform of Hydraulic Excavator under Complex Working Conditions

The rotary platform is the load-bearing substrate of a hydraulic excavator. The dynamic characteristics of the rotary platform directly affect the reliability and safety of the whole machine of a hydraulic excavator. In this work, the characteristics of the main external excitations acting on the hydraulic excavator such as the engine excitation, pressure pulsation excitation of the piston pump, inertial excitation of the working device, and road excitation are analyzed. The vibration transmission paths under the action of external excitations are ascertained. A vibration test method for the rotary platform of the hydraulic excavator is proposed. The vibration characteristics of the rotary platform under complex working conditions are researched, and the internal relationships between the vibration characteristics of the rotary platform and the engine excitation, pressure pulsation excitation of the piston pump, and road excitation are analyzed experimentally. The results show that the rotary platform is subjected to different excitations when it is under different working conditions. Moreover, the internal relationships between the dynamic characteristics of the rotary platform and the external excitation characteristics can be discovered by analyzing the vibration signals of the rotary platform, and the dynamic characteristics of the whole machine of the hydraulic excavator can be deeply studied based on the vibration characteristics of the rotary platform.

Effect of Intentional Mistuning on Dynamic Characteristics of a Energy Turbomachine Bladed Disk

In this article the effect intentional mistuning of an axial turbomachine bladed disk has been analyzed in order to reduce forced response due to low-order engine excitation. The maximum value of forced response of turbomachine rotor’s blades with mistuning parameters is usually much more than the value of the tuned rotors. An increase level mistuning of this critical value actually leads to a decrease magnifications of the forced response. Thus, the actual work has been introducing some degree of intentional mistuning in the design to achieve these purposes. The effectiveness of intentional mistuning has been researched at the design stage of the bladed disk in the energy turbomachines, which is introduced into the rotor’s design by changing the nominal mass of the blades in harmonic models.

Vibration Response of the Crawler Combine Chassis Frame Excited by the Engine

There are many problems of vibration and noise in combine working. As the main power source and excitation source of a combine, the working state of an engine directly affects the reliability and stability of the whole harvester. In order to analyze the vibration response characteristics of a chassis frame under engine excitation, the vibration mechanism and theoretical excitation characteristics of an engine vibration source on a crawler combine harvester are analyzed in this paper, and the vibration response of chassis under engine excitation is tested and analyzed. After theoretical derivation, a two-degree-of-freedom dynamic model of an engine and chassis is established. The experimental results show that the up and down vibration generated by the engine is the main vibration source in the Z direction, and the main excitation frequency is the second-order firing frequency. This paper provides a theoretical reference and experimental basis for vibration reduction and noise reduction of combine and vibration characteristics of the chassis frame.

Natural Frequency Based Topology Optimization of an Aircraft Engine Support Frame

The multi-stage design space refinement (MSDSR) technique increases the likelihood of convergence of topology optimization (TO) with large volume fraction constraints. This work considers MSDSR TO of an aircraft engine support frame with a natural frequency-based objective function. The problem statement maximized the first natural frequency, effectively maximizing the stiffness to mass ratio of the frame. The problem statement considered natural frequency constraints, which eliminated all natural frequencies within 5% of the engine excitation frequency times a safety factor of two. The design space did not consider the initial geometry; therefore, allowing for the determination of the optimal stiffener location on the initial geometry. The results of this work increased the first natural frequency of the engine support frame by 25.9%, eliminated all natural frequencies within 11.3% of the engine excitation frequency, and added only 0.253 kg of mass to the frame. The results of this work further demonstrate the advantages of MSDSR TO and the impact that it can have on the aerospace industry. Specifically, the design space considered in this work allows for the structural reinforcement of a pre-existing design, which is easier to implement and easier to regulate than similar results from the literature.

DYNAMIC CHARACTERISTICS ANALYSIS OF BLADED DISK TURBOMACHINES BASED ON INTENTIONAL MISTUNING

To increase technical level of energy turbomachine in modern turbomachinery, high reliability and durability of structures are required in the design, manufacture and operation of turbomachine. Any change geometry, mass, material properties of the bladed disk of turbomachine in the design is called mistuning parameters. With a small value of mistuning blades can significantly increase amplitude, displacement or stresses of the blades structures. So, analysis influence of the effect mistuning parameters on the dynamic characteristics in the field of turbomachine is an important and urgent task. This article analyzes the effect intentional mistuning of the axial bladed disk turbomachine in order to reduce forced response due to low-order engine excitation. The maximum value forced response of rotor blades turbomachine with mistuning parameters is usually much more than that of the tuned rotors. An increase level mistuning of this critical value actually leads to a decrease magnifications of the forced response. Thus, the actual work has been introducing some degree of intentional mistuning in the design to achieve these purposes. In this paper, we study the effectiveness of intentional mistuning at the design stage bladed disk turbomachine, which is introduced into the rotor design by changing the nominal mass of the blades in harmonic Формаls.

Identification of firefly algorithm-based fluctuation coefficient of the exciting torque for vehicle driveline

The unbalanced excitation force and torque generated by an engine that resonate with the natural frequency of drivetrain often causes vibration and noise problems in vehicles. This study aims to comprehensively employ theoretical modelling and experimental identification methods to obtain the fluctuation coefficients of engine excitation torque when a car is in different gear positions. The inherent characteristics of the system are studied on the basis of the four-degree-of-freedom driveline lumped mass model and the longitudinal dynamics model of vehicle. The correctness of the model is verified by torsional vibration test. The second order's engine torque fluctuation coefficients are identified by firefly algorithm according to the curves of flywheel speed in different gears under the acceleration condition of the whole open throttle. The torque obtained by parameter identification is applied to the model, and the torsional vibration response of the system is analysed. The influence of the key parameters on the torsional vibration response of the system is investigated. The study concludes that proper reduction of clutch stiffness can increase clutch damping and half-axle rigidity, which can help improve the torsional vibration performance of the system. This study can provide reference for vehicle drivetrain modelling and torsional vibration control.

Modal Analysis and Dynamic Behavior for Analytical Drivetrain Model

A generalized dynamic model for an automotive drive train system was detailed to investigate its modal properties and dynamic behavior. The model's engine excitation, clutch, gearbox and disc brake were presented. Then, vibration modes were obtained and classified into clutch, transmission system, disc brake, bearing and combined modes. For each vibration mode, the kinetic and strain modal energies distributions were studied. The dynamic equations were resolved using the numerical Newmark method. The dynamic behavior of the bearings and transmission errors for the two gear stages were studied, and, the effect of the disc brake parameters on the transmission error was analyzed. Finally, a frequency sweep analysis was studied to investigate the system resonance problem.

Torsional Vibration Solutions for Geared Aviation Diesel Engines: Power Transmission Through the Camshaft or Dedicated Internal Driveshaft

Aviation gasoline is in limited supply in many parts of the world although jet fuel is widely available. The turbine engine solution, however, is not a viable option for most of general aviation because of cost. Therefore considerable effort has been expended to develop suitable jet fuel burning compression ignition (CI) engines for general aviation. Because of weight and power concerns in aviation, much of the effort has been directed toward the development of geared engines. Many currently certified geared CI engines, however, require frequent gearbox inspections and have relatively low times before replacement or overhaul. The high pressures produced by CI engines generate torsional vibration that can be troublesome for geared engines. The first mode natural frequency of a drive train can be lowered by increasing its length thereby reducing stiffness so that its convergence with dominant engine excitation harmonics occurs at lower rpm below the high power operating range of the engine. This can be accomplished without increasing the length of the engine and with 2:1 gear reduction by using the camshaft in the case of a four-stroke pushrod engine as the power transmission shaft or a dedicated geared internal power transmission shaft at the desired ratio in the case of an engine with overhead camshafts. Simulation studies show that resonance at the lower speed is associated with a marked reduction in torsional vibration.

Analysis of the influence of engine torque excitation on clutch judder

A simplified three-degree-of-freedom dynamic model with nonlinear friction torque and engine torque excitation, capable of identifying the effect of the engine excitation on clutch judder, is presented. The analysis of harmonic order is performed and a sinusoidal contact pressure between friction surfaces is considered, along with an analytical solution for the relative angular velocity of the clutch plates. The average fluctuation amplitude of the clutch relative angular velocity is used to evaluate the judder. Numerical calculations indicate that the clutch judder increases significantly when the angular velocity of the crankshaft, corresponding to the harmonic orders of the engine, is equal or close to the natural frequency of the driveline. An identical frequency of the engine excitation and the oil pressure fluctuation contributes little to the clutch judder, unless the excitation is at or near the resonance frequency. The amplitudes of oscillations due to the engine excitation grow when the pulsating torque of the engine increases. The mean torque of the engine has little influence on the judder, although it governs the clutch engagement time. The results further show that clutch judder attenuates as the torsional stiffness of the system increases.