11 UNIVERSITY OF PITESTI SCIENTIFIC BULLETIN FACULTY OF MECHANICS AND TECHNOLOGY AUTOMOTIVE series , year XVII , no.21 ( 3 ) TORQUE CONVERTER MODE LLING FOR ACCELERATION SIMULATION 1Ciobotaru, Ticu şor*, 1Vînturiş, Valentin, 2Caravan, Alexandru 1Military Technical Academy, Romania, 2MOND, Romania * e-mail: cticusor2004@yahoo.com KEYWORDS – torque converter, modell ing, simulation, hydrodynamic transmission ABSTRACT – Simulation plays an important role in optimising th e performances of the drive line of the off-road vehicles. The models of the engine, torque conve rter, transmission and running gear are assembled into a large model us ed for estimation of the vehicle acceleration performances. The paper presents a proposal for modelling of the torque converter dimensionless characteristics using segmented continuous func tion taking as variable the inverse of the kinematic ratio. There are analysed the variants of the characteristics offered by the literature as well as the implementation of the torque converter model into the vehicle model. 1. INTRODUCTION The simulation of the acceleratio n and of the tractive performa nces of vehicles plays an important role in optimization of the drivel ine and running gear. The accuracy of the simulation depends dramatically of the m odels used for engine and transmission. Usually, the steady stat e characteristics of the engine are known from the technical specifications provide d by the supplier in terms of variation of the effective power and torque versus engine speeds or, at least, the values of the maximum power and maximum torque and the speeds of the engine. Contrary, the technica l specification of the transmission provide the only the ratios of the gearbox and, sometimes, the maximum torque ratio of the torque converter. The modelling of the driveline imposes the usage of the torque converter characteristics (the variation of the efficien cy, torque ratio and absorbed torque versus slippage) (1). The effort made for modelling th e torque converter characteris tics have focussed on the usage of cubic Spline for fitting data (2) and on the estimation of the torque converter characteristics taking into account the geometry of the pump and turbine rotors (3), (4). Nevertheless, the paper dealing with th e vehicle performances or with the analysis of the automatic transmissions include models based on the fitting of the torque characteristics provided by the supplier (1), (6) or using appropriate tools imp lemented in specialized software such as Dymola (7). Figure 1 Torque converter components 12 Very often, the designers have to roughly estima te the longitudinal dynami cs of the vehicles for different configuration of the driveline ba sed on commercial presentations of the engines and transmissions; such presenta tions usually provide only the ratios of the gearbox and the maximum torque ratio of the torque converter. 2. DIMENSIONLESS CHARACTERISTICS OF TORQUE CONVERTER The dimensionless characteristic of the torque converter represents gr aphically the variation of the efficiency and torque transformation ratio versus the inverse of the speed ratio, defined as: [] ,0 , 1turbine hh impellerniin′′=∈ ; turbine h impellernKn= (1) Figure 2 presents a typical dimensionless characteristic of torque converter (Allison TC-418)/ It may observe that the efficiency curve presents two typical sections: 1. A parabolic shape crossing the origin. 2. A linear shape followed by an abrupt drop for high values of the inverse of the speed ratio. The evolution of the torque transformation ra tio shows two sections too, the shapes being quasi-linear. The two sections mentioned above correspond to the two stages of torque converter work: as torque converter and as hydro-c oupler, respectively; the shifting between the two stages is automatic due to the release of the st