Jang Moo Lee

Performance analysis and parametric design of the dual-mode planetary gear hybrid powertrain

Abstract The multimode electrically variable transmissions (EVTs) are an advancement of the conventional planetary gear hybrid powertrains (PGHPs). Using the analytical methodologies once applied to the single-mode PGHP, the dual-mode PGHP was investigated. The transmission efficiency and the system optimal operation point maximizing the system overall efficiency were analysed. With the system optimal operation points, the fuel economies of the dual-mode PGHP vehicle were calculated assuming constant-velocity cruising and NEDC mode driving. The top velocity and the acceleration performance were also estimated. To assign appropriate parameters for the new system, the design space and the optimization problem were defined using the vehicle performances from the analyses. An approach with various optimization techniques is proposed, and the optimal parametric design is obtained. The dual-mode PGHP showed improvements in efficiency and dynamic performances compared with the single-mode PGHP. In particular, the powertrain is expected to have advantages because it uses a smaller-sized motor/generator (MG) or two identical machines as two MGs.

Efficiency of the planetary gear hybrid powertrain

Abstract The planetary gear hybrid powertrain (PGHP) is known as one of the most efficient configurations for hybrid electric vehicles. The system controls the speed and torque of each component so that it can produce adequate input and output speeds for the optimal operation of the total system. In this paper, the system mechanism is analysed to understand the relation between the input and output speeds. In addition, the transmission efficiency is expressed as a function of three parameters based on the calculation of the net output power. The characteristics of the transmission system showed a large difference from those of a conventional CVT. The speed ratio was the key parameter that affected the efficiency. Furthermore, the performances of the electric motor and generator were decisive factors owing to the loss in the energy conversion. In a simulation on an urban driving schedule, the optimal operation of the engine was able to be obtained, and the system showed an improvement of 2.2 per cent in fuel economy.

Engine operation for the planetary gear hybrid powertrain

Abstract The planetary gear hybrid powertrain (PGHP) is considered as a prospective hybrid electric vehicle (HEV) configuration. However, the optimal control of the system remains controversial because the characteristics of this system are much more complicated than those of conventional systems. This paper presents a case study that reveals the ambiguity of the conventionally-defined optimal operation line. Instead of this engine optimal operation line, the system optimal operation point is suggested. This point is determined by considering the engine efficiency and the transmission efficiency simultaneously. With the system optimal operation point, the fuel economy estimate can be simulated. First, the vehicle cruising at constant velocities was simulated. Then, the vehicle was run at various standard emission test schedules and the mileages were estimated. In each case, the engine operation was analysed to comprehend the optimal operation of the PGHP system. Also, the improvements in fuel economy by optimal operation are presented.

Analysis of dynamic characteristics of structural joints using stiffness influence coefficients

This paper proposes a new modeling method for joints in mechanical structures in order to reduce the errors in eigenvalue analysis due to joint modeling. The new modeling method uses both a stiffness influence method and a condensation method to obtain the dynamic characteristic matrix of the joint region. It also employs the displacement and reaction of finely modeled finite element analysis in the calculation of stiffness influence coefficients. In order to check the validity of the proposed method, natural frequencies and mode shapes of a simple structure with a bolted joint are investigated by the proposed method and by experiments. The eigenvalue analysis using the proposed method shows more accurate results than that using rigid joints modeling, when the natural frequencies are compared with the experimental results. In addition, the differences between the natural frequencies obtained by the proposed method and those by the rigid joints modeling are notable in the modes where the joint has elastic deformation.

Chatter analysis of a parallel mechanism-based universal machining center

Extensive researches have been carried out on machine tool chatter to obtain assessment procedure and improvement measures. In this study, chatter limit is predicted on a newly fabricated universal machining center by the combination of structural dynamic characteristics and cutting mechanics. We showed the unstable cutting conditions, and from them we could plot the unstable borderlines. From the chatter simulations we could say that the newly built universal machining center can be well used in the finishing machining of steel as other common machine tools.

Analysis of a clutch damper using a discrete model

It is important to have a precise model for the clutch damper in order to simulate the entire powertrain of a vehicle and predict the responses of the system. In this research, we developed a new model in which the spring used in the clutch damper is divided into a finite number of elements. The model takes many unique properties of arc-shaped springs into consideration and is anticipated to be more precise than conventional simple models. With the model, two meaningful results were presented which can be utilized afterwards. One is a simulation concerning the peak torque transmitted via the clutch damper. The other is a simulation that shows the hysteretic characteristics of the clutch damper.

A Study on Free Vibration of a Spinning Disk

Without a logical jump, we have derived the governing equation for free vibration of a spinning circular disk by using the variational formulation based upon the Kirchhoff plate theory and von Karman strain one. It has been found during the derivation that the governing equation is theoretically valld under the assumption that in plane deflections are steady and axisymmetric, and that internal forces are linearized while the strains remain nonlinear. The natural frequencies and the critical speeds of a freely spinning disk are obtained approximately and their dependencies on the spinning speed, mode number, and natural freqeuncy of the stationary disk are analyzed.

Specific cutting force coefficients modeling of end milling by neural network

In a high precision vertical machining center, the estimation of cutting forces is important for many reasons such as prediction of chatter vibration, surface roughness and so on. The cutting forces are difficult to predict because they are very complex and time variant. In order to predict the cutting forces of end-milling processes for various cutting conditions, their mathematical model is important and the model is based on chip load, cutting geometry, and the relationship between cutting forces and chip loads. Specific cutting force coefficients of the model have been obtained as interpolation function types by averaging forces of cutting tests. In this paper the coefficients are obtained by neural network and the results of the conventional method and those of the proposed method are compared. The results show that the neural network method gives more correct values than the function type and that in the learning stage as the omitted number of experimental data increase the average errors increase as well.

Experimental Investigation of the Effect of Lead Errors on Helical Gear and Bearing Vibration Transmission Characteristics

The characteristics of gear meshing vibration undesgo change as the vibration is transmitted from the gear to the housing. Therefore, vibration transmission characteristics of helical gear systems must be understood before the effective methods of reducing gear noise can be found. In this work, using a helical gear with different lead errors, the gear vibration in the rotational direction and the bearing vibration are measured. The frequency characteristics of gear and bearing vibration are investigated and a comparson is also provided.

Slip control strategy for an automatic transmission vehicle

Modern automatic transmissions equip torque converters with lock-up clutches to reduce the energy loss of hydraulic systems. Instead of simply engaging the clutch disks, the new technology of clutch slip has been developed to improve the overall efficiency of power transmission. There are two major problems with the clutch slip system. The first is how to keep the slip between the two disks within a small range and the second is when to start or stop the slip. In this paper, the second problem is discussed in view of the vehicle economy. With a simple vehicle dynamic model, the fuel economy is calculated to determine the lock-up strategy. Then the lock-up strategy is developed for a slip schedule.