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The impact of the viscosity and the density of transmission fluids on the performance of a hydraulic torque converter was examined. Four different transmission fluids were evaluated under different operating conditions by fluid temperature and speed ratio. The study utilized the Computational Fluid Dynamics (CFD) method, which modeled the transmission fluid as an incompressible and Newtonian fluid and simulated the flow field inside the torque converter by numerically solving the governing equations of the fluid flow. The simulated flow field of four different fluids were examined via mechanical performance parameters of the torque converter, including the k-factor and the efficiency. The transmission fluids were also experimentally evaluated using the modelled torque converter at two independent laboratories. Comparisons of the model predictions with the experimental results show that the computational data agree well with the test data. A parametric study was performed by using the validated CFD model. The results indicate that the viscosity and the density of the fluid have opposing effects on the performance of the torque converter studied.

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... A torque converter transfers rotating power through the interaction of the fluid and the cascades. Torque converters can provide continuous speed and torque ratios, moreover, it can produce effective damping to protect the transmission system from torsional vibration, thus it is extensively used in automatic transmissions and other hydraulic transmission systems [1]. A typical automotive torque converter includes three wheels: the pump, which is driven by the engine and energises the fluid; the turbine, which discharges the fluid and drives the transmission; and the stator, which is fixed to a one-way clutch ( Figure 1). ...

... The authors sincerely thanks to Professor Houston G. Wood of the University of Virginia for his critical discussion and reading during manuscript preparation. 1 ...

Cavitation inside a torque converter induces noise, vibration and even failure, and these effects have been disregarded in previous torque converter design processes. However, modern torque converter applications require attention to this issue because of its high-speed and high-capacity requirements. Therefore, this study investigated the cavitation effect on a torque converter using both numerical and experimental methods with an emphasis on the influence of the charging oil feed location and charge pressure. Computational fluid dynamics (CFD) models were established to simulate the transient cavitation behaviour in the torque converter using different charging oil pressures and inlet arrangements and testing against a base case to validate the results. The CFD results suggested that cavitating bubbles mainly takes place in the stator of the torque converter. The transient cavitation CFD model yielded good agreement with the experimental data, with an error of 7.6% in the capacity constant and 7.4% in the torque ratio. Both the experimental and numerical studies showed that cavitation induced severe capacity degradation, and that the charge pressure and charging oil configuration significantly affects both the overall hydrodynamic performance and the fluid behaviour inside the torque converter because of cavitation. Increasing the charge pressure and charging the oil from the turbine-stator clearance were found to suppress cavitation development and reduce performance degradation, especially in terms of the capacity constant. This study revealed the fluid field mechanism behind the influence of charging oil conditions on torque converter cavitation behaviour, providing practical guidelines for suppressing cavitation in torque converter.

... The hydraulic torque converter has been widely used in commercial and engineering vehicles due to its function of flexible transmission and torque amplification. In the working process of a hydraulic torque converter, the flow state is very complex, the flow field has a large pressure difference, temperature difference gradient distribution, and the turbulence vortex is complex and variable [1,2], and the cavitation is prone to occur within the torque converter. ...

Aiming at the phenomenon that a high-power torque converter is susceptible to cavitation, which leads to performance degradation, first, a transient flow field model of the torque converter is established, and CFD simulation and experimental research on the torque converter are carried out to find out the speed ratio region where cavitation occurs in the torque converter as well as the rule of occurrence of cavitation, and then the cavitation identification method based on the difference between the inlet and outlet flow of the torque converter is proposed. Then, the transient flow process inside the torque converter is analyzed, and it is pointed out that the angle between the inlet angle of the stator and the outlet angle of the turbine of the torque converter, i.e., the fluid inflow injection deviation angle is an important factor affecting the cavitation phenomenon. By adjusting the key parameters of the stator blade bone line, the fluid inflow deviation angle of the torque converter stator is optimized, so that the speed ratio range of cavitation under large load conditions is greatly reduced from the original 0–0.5 (50%) to 0–0.15 (15%). Meanwhile, in terms of test performance, the nominal torque of the torque converter is greatly improved under the premise of ensuring that the performance is basically unchanged, in which the nominal torque of the test zero speed is increased by 28.7%, and the cavitation of the torque converter has been greatly improved.

The power reflux hydrodynamic transmission system (PRHTS) has the advantages of flexible transmission, low-speed torque multiplication, adaptive adjustment of speed ratio to external load, and improved torque converter (TC) transmission efficiency. Therefore, it is highly suitable for wheel loaders. Wheel loaders usually work in harsh environments with complex and changing working conditions, and static power matching makes it challenging to fully utilize wheel loaders’ performance. In response to the above issues, this paper proposes a dynamic power matching optimization design method for PRHTS with capacity adjustment gear (CAG) based on wheel loader. The optimization design method obtains data through V-shaped working condition experiments of the wheel loader, and conducts clustering analysis on the data to obtain high-frequency kinematic segments and their characteristic parameters. On this basis, combined with the analysis of the working principle of PRHTS, the system structural parameters are optimized and designed. Compared with static power matching, the dynamic power matching optimization design method increases the average traction force by 4.9 kN, improves the transmission efficiency by 2.6%, reduces the average fuel consumption rate by 3.66 g (kW·h) ⁻¹ , and reduces the fuel consumption per V-cycle by 27.7 ml in V-shaped working conditions.

Automotive torque converters have recently been designed with an increasingly narrower profile for the purpose of achieving a smaller axial size and reducing weight. Design of experiment (DOE) and computational fluid dynamics (CFD) techniques are applied to improve the performance of a flat torque converter. Four torque converters with different flatness ratios (0.204, 0.186, 0.172, and 0.158) are designed and simulated first to investigate the effects of flatness ratio on their overall performance, including efficiency, torque ratio, and impeller torque factor. The simulation results show that the overall performance tends to deteriorate as the flatness ratio decreases. Then a parametric study covering six geometric parameters, namely, inlet and outlet angles of impeller, turbine, and stator is carried out. The results demonstrate that the inlet and outlet angles play an important role in determining the performance characteristics of a torque converter. Furthermore, the relative importance of the six design parameters is investigated using DOE method for each response (stall torque ratio and peak efficiency). The turbine outlet angle is found to exert the greatest influence on both responses. After DOE analysis, an optimized design for the flat torque converter geometry is obtained. Compared to the conventional product, the width of the optimized flat torque converter torus is reduced by about 20% while the values of stall torque ratio and peak efficiency are only decreased by 0.4% and 1.7%, respectively. The proposed new optimization strategy based on DOE method together with desirability function approach can be used for performance enhancement in the design process of flat torque converters.

This paper details the capability of PumpLinx® and Simerics® in simulating both Steady-State (Multiple Reference Frame) and transient, three dimensional torque converter performance and predicting the coupling point in a closed torque converter system in automatic transmission. The focuses of the simulation are in predicting the performance characteristics of the torque converters at different turbine to impeller rotating speeds (speed ratios) for 7 different torque converter designs and determine the coupling point at 70°C temperature. The computational domain includes the complex 3D design of all the impeller, turbine and reactor blades, the path ways that the oil travels between the above three components and the leakage gaps between these components. The physics captured in the simulation include the turbulence in the flow field and the rigorous treatment of the Fluid Structure Interaction (FSI) for the one-way free wheel reactor in predicting coupling point. The one-dimensional rotating dynamic modeling of the reactor enables the simulation of the whole range of speed ratios starting from 0 to 0.99. The integrated values of the transient torque on all the rotating components are found out to determine the torque ratio, K-Factor and efficiency. The comparisons with the hardware measurements show less than 5% differences between the test and simulation results. The consistency of the numeric schemes used for the simulation combined with the extremely fast run times and close comparisons with the test measurements adds value to the use of PumpLinx as a tool for simulating full torque converter systems.

Comparative analysis among the capabilities of the RANS, DES, and LES models to predict flow and turbulence distribution was conducted to come up with guidelines for hydraulic torque converter (TC) transient simulation. To ensure the accuracy of calculation, the complex geometry of hydrodynamic elements was accurately represented and the computational meshes of the structured hexahedron were appropriately distributed. Wall shear stress, pressure-streamline structure were analyzed. Compared with RANS, the transient vorticity features, including the birth, development, formation of a scroll; transportation along the blade surface; shedding and rupture at the trailing edge could be clearly captured by the LES and DES models. Rothalpy was used to quantitatively evaluate the hydraulic loss and a new computational formula was proposed to predict the efficiency of each element in TC. After the comparison of relative computing time, DES model was proved be a feasible method for efficiently and accurately simulating 3D unsteady turbulent flow of TC.

A comparative study was carried out on numerical methods for simulating a flow inside a torque converter. To investigate the effect of different methods for handling the relative motion of the parts, three methods were considered – the frozen rotor, sliding mesh and mixing plane methods. To improve the accuracy of performance prediction, the influence of viscosity variation with the temperature was studied by a thermo-fluid analysis. From parametric studies on the numerical scheme and the mesh resolution, it is observed that the results with the frozen rotor and sliding mesh methods agree well with the experimental data, whereas the mixing plane method induces a larger difference. The effect of viscosity variation on the accuracy of simulation is also investigated.

Previously, experimental results for the velocity field in a torque converter pump showed strong jet/wake characteristics including backflows and circulatory secondary flows. To understand the fundamental flow behavior simplified analytical/numerical Navier-Stokes flow models were developed herein to independently analyze the pump pressure-to-suction side jet/wake flow, the core-to-shell side jet/wake flow, and the secondary flows. Parametric studies were undertaken to evaluate the effect that operating conditions and geometry had on the characteristics. Two relatively simple models were employed: (i) a rotating two-dimensional straight-walled duct to model the pressure-to-suction side jet/wake flow due to rotational Coriolis forces and (ii) a 180 deg flow bend to model the core-to-shell side jet/wake flow due to rapid radial/axial flow turning. The formation and development of the pump jet/wake flow was studied in detail. Results showed that the suction side wake, which was due to the counter-rotational tangential Coriolis force, was almost only a function of the modified Rossby number and independent of the Reynolds number. Increasing the modified Rossby number increased the pressure-to-suction side jet/wake flow. A geometric parameter that was seen to affect the pump flow was the backsweeping angle for the pressure-to-suction side jet/wake. Results showed that using backswept blades can completely eliminate the pressure-to-suction side jet/wake flow effect. Other geometrical parameters were tested but only a small to moderate influence on the jet/wake flow phenomena was found. Predicted trends compared favorably with experimental results.

In this paper, the static pressure field and performance parameters of a torque converter pump are measured, analyzed, and interpreted under three turbine/pump speed ratio conditions (0, 0.6, and 0.8). A potential flow code is used to predict the static pressure distribution. Results show that: (1) centrifugal force has a dominant effect on the static pressure rise in the pump; (2) the static pressure field is generally poor at the core section; and (3) the potential flow code can fairly well predict the static pressure distribution at the blade mid-span, but not at the core and shell sections.

A numerical method for calculating three-dimensional, steady or unsteady, incompressible, viscous flow is described. The conservation equations for mass and momentum and the equations of the Îº-Îµ turbulence model are solved with a finite volume method on nonorthogonal boundary-fitted grids. The method employs cell-centered variable arrangement and Cartesian velocity components. The SIMPLE algorithm is used to calculate the pressure and to enforce mass conservation. The computer code is vectorizable as far as possible to achieve an optimal performance on modern vector computers. Results of steady flow calculations in the guide vane, the pump rotor, and the turbine rotor and of the unsteady interaction simulation of the pump and the turbine of a one-stage one-phase non-automotive hydrodynamic torque converter are presented.

The three-dimensional average velocity field in an automotive torque converter turbine was examined. Two significantly different operating conditions of the torque converter were tested: the 0.065 and 0.800 turbine/pump speed ratio. Velocities were measured using a one-directional, frequency-shifted laser velocimeter. The instantaneous angular positions of the torque converter turbine and pump were recorded using digital shaft encoders. Shaft encoder information and velocities were correlated to generate average velocity blade-to-blade profiles and velocity vector plots. Measurements were taken in the inlet, quarter, mid, and exit planes of the turbine. From the experimental velocity measurements, mass flows, turbine output torque, average vorticities, viscous dissipation, inlet incidence flow angles, and exit flow angles were calculated. Average mass flows were 23.4 kg/s and 14.7 kg/s for the 0.065 and 0.800 speed ratios, respectively. Velocity vector plots for both turbine/pump speed ratios showed the flow field in the turbine quarter and midplanes to be highly nonuniform with separation regions and reversed flows at the core-suction corner. For the conditions tested, the turbine inlet flow was seen to have a high relative incidence angle, while the relative turbine exit flow angle was close to the blade angle.

The objective of this paper is to improve the performance estimation model of the internal flow field of a torque converter.
Compared with performance experiment results, the converter based on the one-dimensional model does not satisfy the performance
requirements demanded in practice. Therefore, we need to develop more predictable and reliable performance estimation models.
In order to obtain shape information on three-dimensional blade geometry, a process of reverse engineering conducts a torque
converter assembly, impeller, turbine and stator. In addition, a CFD simulation including mesh generation and post-processing
was carried out to extract equivalent parameters from the internal flow field. The internal flow field can be explained by
analyze the correlation between a performance estimation model and CFD analysis. The equivalent performance model adopts the
variation of energy loss coefficients for a given operating condition according to the application of a changing energy loss
coefficient by the least mean squares method. The estimated equivalent model improves the agreement in performance between
experiments and the theoretical model. This model can reduce the error to within about 3 percent. Furthermore, this procedure
for predicted performance achieves eminence in the estimation of the capacity factor.

A new k-[epsilon] eddy viscosity model, which consists of a new model dissipation rate equation and a new realizable eddy viscosity formulation, is proposed in this paper. The new model dissipation rate equation is based on the dynamic equation of the mean-square vorticity fluctuation at large turbulent Reynolds number. The new eddy viscosity formulation is based on the realizability constraints; the positivity of normal Reynolds stresses and the Schwarz' inequality for turbulent shear stresses. We find that the present model with a set of unified model coefficients can perform well for a variety of flows. The flows that are examined include: (i) rotating homogeneous shear flows; (ii) boundary-free shear flows including a mixing layer, planar and round jets; (iii) a channel flow, and flat plate boundary layers with and without a pressure gradient; and (iv) backward facing step separated flows. The model predictions are compared with available experimental data. The results from the standard k-[epsilon]

Computational Fluid Dynamics Simulation of Hydraulic Torque Converter for Performance Characteristics Prediction

- S Jeyakumar
- M Sasikumar

Parametric Analysis and Optimization of Inlet Deflection Angle in Torque Converters

- C Liu
- A Untaroiu
- H G Wood
- Q Yan

Hydrodynamics of the Hydraulic Torque Converter

- E W Spannhake