Assessment of the switching time and fluid type influence on the transient quality in hydro-mechanical systems

The number of transients in hydro-mechanical power transmissions accounts for a significant portion of the total operating time and has a significant impact on drive economy. The quality of the transients largely depends on their duration and the type of working fluid used. The purpose of the work is to analyze the transients in the hydro-mechanical system, taking into account the effect of the duration of switching processes and the type of working fluid used. Determination of transient parameters in the hydro-mechanical power transmission was performed on the basis of mathematical dependences describing the switching process of two torque converters depending on the duration of the filling and emptying process and the influence of the type of working fluid used. Analysis of the calculated characteristics of transients in hydromechanical power transmissions showed that the main factor in the switching of torque converters, is the combination of filling and emptying processes, depending on the type of working fluid used. The obtained results give grounds to propose recommendations on coordination of filling and emptying processes in order to increase the efficiency of the hydromechanical drive.

Effect of the blade shaped by Joukowsky airfoil transformation on the characteristics of the torque converter

Cavitation is common in traditional torque converters whose blades are designed by beam theory; the blade curvature is discontinuous and cannot be analysed by functions. In this paper, the YJH265 torque converter is used as the prototype to reconstruct the stator blades with Joukowsky airfoil transformation. Computational Fluid Dynamics (CFD) is used analyse the flow field in the torque converter with the three-dimensional transient full flow channel. Combined with experiments, cavitation is found at the exit of the YJH265 torque converter stator. This is the same as the cavitation position of different torque converters studied by other scholars, and the flow state at the simulation outlet is high vacuum, boundary layer separation and high turbulent kinetic energy. Without changing the angle and chord length, the stator blades were reshaped and simulated with the optimised Joukowsky airfoil. As a result, the boundary layer separation phenomenon disappeared, the vacuum degree and turbulent kinetic energy were reduced, the torque ratio increased by 0.175 (5.6%), and the efficiency increased by 4.9%. To conclude, the optimised Joukowsky airfoil can be used in the design of stator blades, and its streamline is consistent with the fluid dynamics characteristics, which greatly reduces the probability of cavitation and improves the performance and service life of the torque converter.

KINEMATICS OF MULTI-STAGE MATCHING GEARBOXES FOR HYDRODINAMIC TORQUE CONVERTERS

The study offers a design solution for online capacity adjustment of hydrodynamic torque converter powertrains. It is proposed to install a step-less speed drive or multistage matching gearbox between the engine and the torque converter to adjust the powertrain properties on the move depending on the current operating conditions. We propose the matching device arrange-ments. The solutions can be used in buses, trucks, tractors, diesel locomotives, etc. that operate in a wide range of external loads.

Parametric Analysis and Optimization of Leaning Angle in Torque Converters

Torque converters are durable fluid couplings that can provide output torque multiplication. Blade leaning angle represents the angular position of a blade chord with respect to its radial reference line, and it is an important blade variable regarding both hydrodynamic performance and manufacturability of a torque converter. In traditional design processes, blade leaning angles are often determined based on experiences of engineers; hence, this study proposed a design approach using the combination of computational fluid dynamics (CFD) and optimization. Two CFD models were developed to design blade leaning angles. A steady-state periodic CFD model was employed for the parameter study and the optimization, and a transient full three-dimensional (3D) model was performed to study the flow mechanism and evaluate the performance with higher accuracy. Design of experiment (DOE) technique was employed to investigate the relationship between blade leaning angles and hydrodynamic performance, and a reduced cubic model was derived from the results. It was found that blade leaning angles had profound effects on torque converter performance; a large blade leaning angle intensified the flow blockage effect, thus resulting in a lower mass flowrate and torque capacity. Seven torque converters with different blade leaning angles were tested to validate the obtained numerical results, and the test data were found to be in good agreement with the CFD predictions. Finally, the hydrodynamic performance of the base model torque converter was optimized by a multi-objective genetic algorithm.

On the application of passive flow control for cavitation suppression in torque converter stator

Purpose The purpose of this paper is to study the transient cavitation process in torque converters with a particular focus on cavitation suppression with a passive flow control technique. Design/methodology/approach The transient fluid field in a torque converter was simulated by RANS-based computational fluid dynamics (CFD) in a full three-dimensional (3D) model. A homogeneous Rayleigh–Plesset cavitation model was used to simulate the transient cavitation process and the results were validated with test data. Various secondary flow passages (SFP) were applied to the stator blade. The cavitation behavior and hydrodynamic performance were simulated and compared to investigate the effect of SFP geometries on cavitation suppression. Findings Presented results show that cavitation in the torque converter is highly unstable at stall operating condition because of the combination of a high incidence angle and high flow velocity. The addition of an SFP to the stator blade produces a disruption of the re-entrant jet and reduces the overall degree of cavitation, consequently inhibiting the unstable cavitation and reducing performance degradation. Originality/value This paper provides unique insights into the complicated transient cavitation flow patterns found in torque converters and introduces effective passive flow control techniques useful to researchers and engineers in the areas of fluid dynamics and turbomachinery.