Engine Excitation Frequency Research Articles

Modelling and Vibration Analysis of a Parallel Hydraulic Hybrid Vehicle

In this paper, the vibration characteristics of a parallel hydraulic hybrid vehicle (PHHV) powertrain are investigated. A powertrain model is built to capture the natural frequencies and mode shapes before model reduction is conducted to simplify the system complexity. The natural frequencies and the mode shapes of the PHHV are compared with the original vehicle. Results show that with a hydraulic pump/motor (HPM) added on the powertrain, the dynamic response to engine excitation is increased only at the first natural frequency. Due to the minimum engine excitation frequency being higher than the first natural frequency of the system, resonance is avoided. The HPM also introduces excitation to the PHHV powertrain due to its instantaneous torque fluctuations. As HPM excitation is much smaller than the engine excitation, it does not produce excessive vibrations even though the powertrain frequency response is near its lowest resonant frequency. These results indicate that the NVH characteristics of the powertrain are not significantly influenced by the significant changes to the system architecture resulting from the addition of the HPM. Additionally, the HPM is not exposed to significant sources of vibration from the forced responses of the engine. Consequently, the need for substantive vibration isolation for the HPM is reduced.

Topology optimization of a pre-stiffened aircraft bulkhead

The bulkhead of an aft-fuselage twin-engine mounted aircraft is a pivotal structural component from a noise and vibrations perspective as it is the main transmission path for the engine-induced vibration to propagate into the passenger cabin. Despite this, there has yet to be a successful implementation of topology optimization (TO) on a pre-stiffened aircraft bulkhead. This work is the first to investigate TO on a pre-stiffened bulkhead with a frequency-based problem statement. The objective function was set to maximize the first eigenfrequency to maximize the stiffness to mass ratio of the bulkhead. Frequency constraints were implemented to eliminate the natural frequencies within range of the engine excitation frequency. A volume fraction constraint was set such that the mass of the solution was less than the mass of similar bulkhead stiffeners reported in the literature. The first successful implementation of topology optimization on a pre-stiffened aircraft bulkhead was obtained. Two designs satisfying the optimality criterion were generated, both of which were able to improve bulkhead structural integrity, reduce mass, and eliminate resonance from ± 10% of the engine excitation frequency. This work demonstrates that TO is a useful tool to help aerospace engineers improve the vibro-acoustic properties of the bulkhead without sacrificing mass or structural integrity. The methodology introduced in this work can be easily integrated into aircraft design, as it uses tools widely available in the aerospace industry.

Investigation of the Effect of Rotation Speed on Vibration Responses of Transmission System

In the operating process, it is found the vibration of main reducer reaches a maximum value when certain types of vehicles are running at a speed around 4000 RPM. However, how the rotation speed of engine affects the vibration responses to automobile transmission system has not been investigated theoretically in details. To investigate this problem, the transmission system of automobile is simplified to a drive-final shaft system in this research, and a coupled vibration model of drive-final shaft system is developed. This model is used to simulate the vibration response to transmission system at different rotation speeds. Simulation results show that the torsional vibration responses reach the maximum when the rotation speeds are 3800 RPM and 4200 RPM and the vibration responses of pinion reach the maximum value when the rotation speeds are 4000 RPM and 4200 RPM. Moreover, finite element analysis is conducted to investigate the reason for this phenomenon. It is found that the torsional vibration responses reach the maximum value when the excitation frequency of engine is close to the resonance frequency of drive shafts. This research provides an effective method to analyse the vibration characteristics of automobile transmission system.

A Pipe Routing Method Considering Vibration for Aero-Engine Using Kriging Model and NSGA-II

The computer-aided design optimization and vibration analysis, especially avoiding resonance are fundamental challenge to piping system design of complex products. Conventional pipe design methods commonly focus on either automatic geometry layout or vibration analysis, which usually leads to repeated modifications between both disciplines. In this paper, a multi-objective pipe routing algorithm considering vibration performance for aero-engine is presented based on Kriging model and non-dominated sorting genetic algorithm-II (NSGA-II), where pipe length, smoothness, and natural frequency are taken into account. Pipe node positions are optimized by using NSGA-II subject to several constraints. In order to improve computational efficiency, a Kriging model reflecting the relationship between the pipe node position and natural frequency is constructed, and then is applied instead of computer-aided engineering analysis program to evaluate the individual fitness during evolutionary computations. Several numerical computations are performed on a simplified piping model, and the results show that the constructed Kriging model can guarantee high modeling accuracy and the presented routing algorithm is able to obtain a set of non-dominated solutions of pipe layouts, in particular, the natural frequency of pipes are far from engine excitation frequency, which guarantees to avoid possible resonance.

A Car Exhaust System Hook Position Optimization Analysis

Based on the study of a car exhaust system, use HyperMesh Software and its build-in finite element software to build FEM , Analysis the free modal of exhaust system, Calculate its natural frequency, Then optimize the position of hook based on the ways of average degrees of freedom (ADDOFD), Makes its modal frequencies avoiding engine idling frequency. Finally, through the calculated constraint mode, Verify whether coupling with the excitation frequency of engine, and further verify the reasonableness of the position of the hook.

Finite element analysis and experimental investigations of the back case of a transmission with a central brake

Because of limitations in the vehicle layout, a central brake system was installed directly on the transmission’s back case of a certain type of medium-size truck. Under the condition of emergency braking, the back case easily fails because of the large braking torque. In this paper, a method of structure improvement, finite element analysis and experimental investigations of the transmission’s back case was proposed. Two improved designs of the back case are discussed. The finite element analysis results indicated that the improved back case was capable of bearing the maximum braking torque, which was also verified by vehicle road tests and torque tests. The modal analysis results implied that the lowest free modal frequency of the improved back case was increased and far away from the engine excitation frequency. In addition, the first-order constrained modal frequency was also greater than the gear meshing frequency. The overall results implied that the improved design of the transmission’s back case was applicable under normal conditions, and the proposed method was sufficiently accurate for wide use.

Optimum Design of Engine Test Bench Based on Finite Element Analysis

A test bench of vehicle engine is designed and the three-dimensional solid model is established in UG software. Then the model is imported into ANSYS software to conduct static stress analysis, the stress and deformation distribution of test bench are obtained, referenced the results and the bracket are optimized to improve support ability, the maximum stress and the maximum displacement of test bench decreased 66.9% and 76.9%, respectively. Lastly modal analysis of test bench is performed, the chassis base is strengthen design according to the first-order mode shape, then the first natural vibration frequency is heightened 91.0%, it is far away from the engine excitation frequency range, the stability of test bench is enhanced.

DESIGN OPTIMIZATION OF MARINE ENGINE-MOUNT SYSTEM

Design optimization of marine engine–mount system for vibration control is presented in this paper. The engine is modelled as a rigid body with supports connected to a rigid floor. The mounts are modelled as three-dimensional isolators with hysteresis damping. The objective is to select the stiffness coefficient and orientations of individual mount in order to minimize the vertical force transmitted from the engine to the floor to control the structure-borne noise. Constraints are imposed to keep the isolator static and dynamic deflection within the desired limits and a minimum gap between system natural frequency and engine excitation frequency for avoiding possible system resonance. The sequential quadratic programming (SQP) technique has been applied as the optimization algorithm. The typical force and moment of a 4-stroke engine with one cylinder is analyzed and input in the optimization system. The results of optimization are compared with that of a conventional engineering design with the isolators working under their maximum allowable deflection. This comparison shows that, as compared with force transmission of the conventional isolation system, the value of optimized system is only half for multi-frequencies excitation and one-fourth for single frequency excitation. The mechanism of vibration isolation involved in the optimization is investigated with the frequency response of the system. Sensitivity study of the system with the variation of the design parameters is also carried out and proves that the minimum obtained is the global value in the range of design parameters.