Jibin Hu

Study on Aeration for Disengaged Wet Clutches Using a Two-Phase Flow Model

The existing computational models for disengaged wet clutches are deduced based on the single-phase flow theory. However, the complex gas-liquid two-phase flow is formed due to aeration at high rotational speeds. The objective of this study is to use a two-phase flow model to demonstrate the aeration process at different rotational speeds not only of the friction plate but also of the separator plate. A nongrooved, steady-state, two-phase flow computational fluid dynamics model is built using FLUENT , and it is validated by experimental data. The results reveal that air enters the clearance at a critical rotational speed, which causes the drag torque to sharply decrease. The aeration mode and flow pattern are obtained via simulations. The rotational speed of the separator plate has a significant effect on the aeration, including the speed magnitude and direction.

Modeling of electromagnetic torque considering saturation and magnetic field harmonics in permanent magnet synchronous motor for HEV

Abstract Electromagnetic torque ripple of permanent magnet synchronous motor (PMSM) causes electro-mechanical coupling vibration and noise in hybrid electric vehicle (HEV). However, the traditional mathematical model of PMSM cannot absolutely reflect the reason of torque ripple and variation on the different operation performance of the motor for HEV. The purpose lies in the fact that electromagnet factor originated torque ripple and variation have been taken into account in the mathematic model of PMSM. Based on the classical Parks transformation theory and the Fourier series analysis of magnetic field, a general nonlinear mathematical model of PMSM considering saturation and magnetic field spatial harmonics and time harmonics is presented in this paper. The general analytical model cannot only taking into account the variation of electromagnetic parameters caused by electric vehicle operating, but also can explain the frequency and the order of torque ripple theoretically. The models effectiveness is tested through finite element analysis simulations and some experimental results. The analytical model presented here can be used for the characteristic analysis, the drive system dynamic precise analysis and fault diagnose of PMSM for HEV.

Theoretical and Experimental Study of Cavitation Effects on the Dynamic Characteristic of Spiral-Groove Rotary Seals (SGRSs)

A theoretical model is developed to analyze oil-film stiffness and damping coefficients of SGRSs using two different cavitation models, i.e., the Reynolds and JFO boundary conditions. By applying the small perturbation method, the steady and perturbed Reynolds equations could be obtained. The control volume method was used for the spiral grooves, and the upwind scheme was applied to improve the convergence of the solution. The performance of the computation algorithm was studied by analyzing the mesh dependencies and computing power. A new test setup was built to measure oil-film stiffness, to verify the theoretical models, and to study the validity of the Reynolds and JFO boundary conditions. A representative SGRS was analyzed at different operating speeds and inlet pressures to investigate the occurrence of cavitation and the dynamic characteristic. The effect of the spiral-groove parameters on the dynamic characteristics is also discussed.

Dynamics of a hydraulic-transformer-controlled hydraulic motor system for automobiles

This paper presents a hydraulic-transformer-controlled hydraulic motor system for automobiles. The system consists of a hydraulic common pressure rail, a hydraulic transformer and a hydraulic pump–motor. The inherent dynamic characteristics of the system are investigated by an analytical method. The results are validated by simulations and tests. Because of the symmetrical mechanical structure of the valve plate in the hydraulic transformer, the system has both minimum-phase characteristics and non-minimum-phase system characteristics. The negative response characteristics of the system appear if the controlled angle is larger than 30°. The non-minimum phase of the system is unavoidable and should be considered in the controller design of the system. The stiffness of the system is also lower than those of the pump-controlled and valve-controlled systems. The stiffness changes with the variation in the controlled angle and becomes higher with increasing controlled angle.

On–off motion of a hydraulic free-piston engine

The current paper presents the on–off characteristics of a compression ignition single-piston hydraulic free-piston engine. A pilot control circuit and a control method for on–off control of the engine are introduced. Detailed piston motion under on–off control of the engine is investigated. The results indicate that the piston on–off motion of 1 cycle can be divided into a pilot phase and a wave phase. The piston motion in the pilot phase is determined by the flow capacity of the frequency control valve. The piston acceleration during the accelerated compression process peaks in the pilot phase. The wave phase consists of a rebound stage, a decaying stage and a creep stage. The rebound stage determines the initial conditions of the other two stages and affects the piston frequency control. The control method proposed is immune from the bottom-dead-centre cycle variation. A high piston frequency results in a better engine fuel economy.

Flow dynamical behavior and performance of a micro viscous pump with unequal inlet and outlet areas

ABSTRACT The micro viscous pump is an important type of fluidic device. Optimizing the working performance of the pump is crucial for its wider application. A micro viscous pump design with unequal inlet and outlet areas is proposed in this paper. The flow field of the viscous pump is investigated using 2D laminar simulations. The mass flow rate and driving power are studied with different opening angles. The effects of the Reynolds number and the pressure load on the working performance are discussed in detail. Flow structures and vortex evolution are analyzed. With larger inlet and outlet areas, a higher mass flow rate is obtained and less driving power is achieved. A high pressure load results in a reduction in mass flow rate and an increase in driving power. Pumps with large opening angles are more susceptive to the Reynolds number and the pressure load. The adverse impact of the pressure load can be reduced by increasing the rotor speed. The vortex structure is affected by the geometric and operating parameters in the flow field. The flow dynamical behavior of the viscous pump exerts significant influence on its pumping ability. The present work gives rise to performance improvements for the micro viscous pump.

Analysis of torsional vibration in an electromechanical transmission system

Aiming at the torsional vibration in the electromechanical transmission system, this article introduces the active vibration method and analyzes the vibration characteristics on the condition of the external excitation, and then, the condition of the permanent magnetic synchronous motor parameter is obtained. In the braking energy recovery working condition, the permanent magnetic synchronous motor is operated in generator mode and is subjected to power control, this cause it to produce negative effect of damping. Negative effect of damping leads to the increasing torsional vibration. Then, the improved power control strategy is introduced to reduce the vibration. Computer simulations are used to demonstrate the active vibration method and the effectiveness of the proposed control strategy, which provides reference for the design of electromechanical systems in the hybrid electrical vehicles.

Chapter 4 – Transmission Architecture and Topology Design of EVs and HEVs

Abstract For electric vehicles (EVs), the motor is used as the power source to drive the vehicle. According to the arrangement of motors, there are four configurations: single-motor driving, dual-motor independent driving, wheel-motor driving, and dual-motor front- and rear-axle independent driving. In general, hybrid EVs can be crudely divided into three types: parallel, series, and split. Among all three types, the power-split type is the most popular. This is mainly because the engine in a power-split hybrid vehicle is decoupled from vehicle speeds and can operate efficiently even when much of the power flows in the mechanical path. In this chapter, a novel and efficient methodology is presented for the design of power-shifting transmissions (PSTs). The keys of the methodology are the degree of freedom model of the PSTs and the basic configurations. An algorithm of mini-max solution for the overdetermined equations is applied to design the gear ratios. Furthermore, the design concept can also be applied to the other fixed gear transmissions, such as automated manual transmissions and dual-clutch transmissions.

Configuration synthesis of electric-drive transmissions for tracked vehicles

This article focus on the configuration synthesis of electric-drive transmissions for tracked vehicles. First, a new graph theory model is proposed to represent the transmission mechanism, which makes the complex transmission system easier to understand. Second, a configuration synthesis method is proposed based on kinematics and statics, in which the speed degree of freedom and torque degree of freedom are considered as the constraints of configuration synthesis. Also, the expressions for speed degree of freedom and torque degree of freedom are derived. Third, based on the graph theory model, the necessary condition to achieve skid steering in the transmission of tracked vehicles is obtained. The results of this article can provides a theoretical basis for the design and analysis of transmission mechanism of tracked vehicles.

Analysis of torsional stability and the dynamical characteristics of electromechanical systems

Electromechanical couplings have been reported to play a crucial role in determining important behavior of nonlinear systems. In this study, we analyzed the nonlinear dynamic characteristics of the electromechanical coupling system. First, considering the electromechanical coupling effect of the system, differential equation of the system was obtained by combining the Park equation of a permanent-magnet synchronous motor with the rotor dynamics equation. Then, the coordinate plane projection method was used to analyze the chaotic phenomenon of the electromechanical coupling system. Through calculating the weight value of the 10 projection planes of the electromechanical coupling system, four projection planes with smaller weight values were chosen. Finally, the analysis of the four projection planes of the system indicated that the whole system could reach to the stable state by only controlling the rotational speed in the steady state. In this perspective, the 5-degree-of-freedom system reduced to 2-degree-of-freedom system. Our results would help us create an electromechanical coupling system with a control strategy.