Numerical Analysis of the Torque Converter Stator Blade by the Boundary Element Method

<div class="htmlview paragraph">The performance of a large-volume production torque converter is slightly different from those of development prototype due to the core leakage flow. The sealing gap between the stator crown and pump or turbine core of the production converter is usually larger than that of prototypes because of fabrication method and tolerances. In this work, the core leakage flow of torque converter was investigated using CFD. The core region was modeled and coupled together with other three major components of a converter. Studies show that for a particular converter the core leakage flow could result in a 3.6% stall torque ratio reduction and a 2% peak efficiency decrease. The effects of sealing gap dimensions were also studied.</div> <div class="htmlview paragraph">Computational investigations in this work indicated that the variation of input K factor with input torque level observed in dyno tests is due to the cavitation in the torque converter. Cavitation occurs at high input torque and low speed ratio conditions because of the high volume flow rate and large incidence angle at the stator inlet. The torque converter performances at different input torque levels were predicted by CFD simulations with a cavitation model. A new concept of the maximum input torque of a torque converter, which is limited by cavitation, is presented. The engineering solutions to reduce converter cavitation are also discussed in this paper.</div>

<div class="htmlview paragraph"> </div> <div class="htmlview paragraph"> </div> <div class="htmlview paragraph">The quality of exhaust sound has become one of the important factors in the motorcycle market.</div> <div class="htmlview paragraph"> </div> <div class="htmlview paragraph">Therefore both an efficient sound quality evaluation method and technology to achieve ideal sound quality have become necessary.</div> <div class="htmlview paragraph"> </div> <div class="htmlview paragraph">Sound qualify evaluation has generally been performed by trial and error through repeated modification of exhaust silencer construction until desired quality was obtained.</div> <div class="htmlview paragraph"> </div> <div class="htmlview paragraph">But it usually took painstaking work and long hours.</div> <div class="htmlview paragraph"> </div> <div class="htmlview paragraph">In order to solve such problems, we established an objective auditory evaluation method.</div> <div class="htmlview paragraph"> </div> <div class="htmlview paragraph">We also applied Principal component analysis to analize the result of the “Semantic Differential Method (SD method)” so as to determine the affecting elements.</div> <div class="htmlview paragraph"> </div> <div class="htmlview paragraph">Through this analysis system, “powerful sound” caused by relatively higher content of the low frequency range and “crispy sound” caused by a cyclic sound pattern were determined to be desirable sounds for “American type” motorcycles.</div> <div class="htmlview paragraph"> </div> <div class="htmlview paragraph">We established a system for approximate frequency distribution characteristic estimation for simply constructed exhaust silencers by introducing a numerical computation method, called “Finite Element Method (FEM)” and “Boundary Element Method(BEM)” to estimate the sound when exhaust silencer component elements are modified.</div> <div class="htmlview paragraph"> </div>

<div class="section abstract"><div class="htmlview paragraph">Automatic transmission (AT) is a complex hydroelectromechanical system, since it consists of hydraulic, electrical and mechanical parts.</div><div class="htmlview paragraph">On cars produced by “UzAuto Motors” mainly AT of the 6T family, 6-speed AT family GM: 6T30, 6T40, 6T45, 6T50 “Hydra-Matic” are used.</div><div class="htmlview paragraph">Production of parts of these transmissions is carried out both at American GM plants and at GM plants in China and Korea.</div><div class="htmlview paragraph">The differences between AT 6T30/6T40/6T45/6T50 are in the thickness of the output chain and in the planetary gear, in the sizes of some other units and the housing itself. But the differences are much more influenced by the settings of the transmission unit, which select operating modes with different engines so as not to overload the thinnest places of the automatic transmission.</div><div class="htmlview paragraph">Automatic transmissions 6T30, 6T40, 6T45, 6T50 have the ability to manually shift gears and activate the “kickdown” mode (for quick acceleration of the car, when you sharply press the gas “all the way” it makes the automatic transmission downshift, and sometimes by two steps).</div><div class="htmlview paragraph">The operation of the transmission is controlled by various electronic systems that are responsible for the operability and structural integrity of the gearbox.</div><div class="htmlview paragraph">Failure of the automatic transmission can occur as a result of one or a combination of malfunctions of the following parts: in the torque converter; in the mechanical part of the gearbox; in the hydraulic part of the control system; one or more clutches of the gearbox; in the electrical part of the control system; in the electronic control unit.</div><div class="htmlview paragraph">The authors of the work investigated and determined the occurrence of malfunctions and failures depending on the temperature of the working fluid of the automatic transmission of a passenger car.</div><div class="htmlview paragraph">Also, the dependence of the resource of the automatic transmission on the temperature of the hydraulic fluid was obtained. High-quality diagnostics of the automatic transmission and its control system can in many cases save the car owner from expensive repairs: <ul class="list disc"><li class="list-item"><div class="htmlview paragraph">without thorough diagnostics, the automatic transmission cannot be subjected to routine or major repairs. Only on the basis of diagnostic information can a conclusion be made about the technical maintenance or repair of the automatic transmission;</div></li><li class="list-item"><div class="htmlview paragraph">based on real experience of operating passenger cars equipped with automatic transmission, we recommend changing the oil every 35000 miles under operating conditions in Tashkent. We also recommend conducting diagnostics of the automatic transmission every 12500 miles of the car's mileage.</div></li></ul></div></div>

<div class="htmlview paragraph">This paper presents a general discussion of automatic transmission parasitic losses and efficiency characteristics.</div> <div class="htmlview paragraph">Efficiency characteristics of the three major automatic transmission components-pump, torque converter, and gearbox-and their contribution to the transmission total torque losses are examined. A data reduction method for isolating gearbox torque losses from total transmission losses is also described.</div> <div class="htmlview paragraph">The information presented is based on pump, torque converter, and transmission testing performed at SwRI for Ford Motor Company. Test data was used to perform analytical fuel economy benchmarking studies. Testing included 13 transmissions manufactured by American, European, and Japanese manufacturers for 3.0-5.8L truck applications.</div>

<div class="section abstract"><div class="htmlview paragraph">The objective of this investigation is to characterize the torsional characteristics of the hydrodynamic torque converter. Analytical and experimental techniques are used to quantify the relationship between torsional oscillations imposed on the pump to those at the turbine as a function of frequency, operating point and design. A detailed model of the hydrodynamic torque converter based upon one-dimensional flow theory is used to establish fundamental torsional behavior independent of the downstream mechanical system. A simplified linear spring-mass-damper representation of the hydrodynamic torque converter is derived whose coefficients are proportional to pump speed for a particular design. A transmission dynamometer test cell with the capability to produce torsional oscillations was used to develop frequency response functions for various torque converters in a transmission, operating at steady state conditions. It was found that the torque converter behaves like a low pass filter with a cutoff frequency dependent upon operating speed, torque and design. Angular vibrations below 20 Hz were found to pass through the torque converter with sufficient energy to excite natural frequencies of downstream drivetrain components.</div></div>

<div class="section abstract"><div class="htmlview paragraph">This paper details testing for torque converter clutch (TCC) characterization during steady state and dynamic operation under controlled slip conditions on a dynamometer setup. The subject torque converter under test is a twin plate clutch with a dual stage turbine damper without a centrifugal pendulum absorber. An overview is provided of the dynamometer setup, hydraulic system and control techniques for regulating the apply pressure to the torque converter and clutch. To quantify the performance of the clutch in terms of control stability, pressure to torque relationship and the dynamic behavior during apply and release, a matrix of oil temperatures, output speeds, input torques, and clutch apply pressures were imposed upon the torque converter. The torque capacity of the clutch is estimated with the dimensions of the friction surfaces and pressure plate and an enhanced lookup data of K-factor obtained through testing of the hydrodynamics at input torques from 10 to 200 Nm over a speed ratio range consistent with controlled slip. The influence of controlled operating point parameters is reported as TCC apply pressure verse estimated TCC torque. The effect of temperature, output speed and the sign of input torque are shown to a departure from the normally assumed linear relationship between pressure and torque. The results and procedures presented can be utilized to improve in vehicle control schemes through more accurate pressure to torque gain scheduling.</div></div>

Hydraulic torque converter is widely used in transmission units as it is able to provide variable speed and torque ratio, isolate vibration, and absorb shock. The pursuit of a highly packed power unit requires a high capacity/speed torque converter, consequently resulting in a higher risk for cavitation and severe performance degradation, noise, vibration, and even failure. Existing cavitation models generally focus on water, and the empirical parameters are not suitable for the cavitation prediction of torque converter which utilizes high viscosity oil as its working medium. This paper focused on the influence of parameters on the performance and cavitation characteristics of torque converter. A full flow passage geometry and different computational fluid dynamics (CFD) models with cavitation were developed to predict torque converter fluid behavior by resolving Reynolds-averaged Navier–Stokes equations using finite volume method (FVM). The numerical results indicated that nuclei volume fraction, vaporization coefficient, mean nucleation site radius, and maximum density ratio have great influences on the cavitation behavior. These parameters altered the degree of cavitation and the pressure distribution on the surface of stator blades, and affected the stall performance such as stall capacity factor and torque ratio. The cavitation model was then modified to improve calculation accuracy. The test results showed that the prediction error under stall operating condition was decreased from 6.7% to 2%. This study provides insight on the influences of the empirical parameters on both internal cavitation behavior as well as overall hydrodynamic performance.

<div class="section abstract"><div class="htmlview paragraph">It is common that angular velocities can be different from time to time between an engine output and transmission input, because both are connected by a damper in torque converter with flexible elements in it. When this difference occurs abruptly for some reasons, an internal impact could start between the engine-attached members (also known as driving members) and the transmission-attached members (or driven members). The resulting impact load could be several times the torque an engine’s combustion force can generate, depending on the impact energy. An impact load can be very devastating to a torque converter and other power-train members, just as to all other mechanical systems. This work presents a comprehensive and interesting study to help understand the rotational impact behavior for a system where none of bodies is stationary at the onset of impact. Using an explicit finite-element solver for case studies, the author will assess what role a friction-based clutch, placed between the engine and vibration-isolating damper, will play, by limiting the passage of engine’s kinetic energy to some degree. It is interesting to find that it is the relative, not the absolute, angular velocities of impacting bodies that dictate the outcomes of an impact event.</div></div>

Cavitation is a transient phase transition between liquid and vapor, and it often occurs in fluid machinery, especially in a hydraulic torque converter that uses oil as the working medium to transmit speed and torque. The complex and strongly coupled fluid flow in the torque converter is prone to cavitation due to high rotating speed and high-temperature working conditions. Cavitation seriously affects the working performance, transmission smoothness, and service life of the torque converter. The flow pressure in the stator of a torque converter under various charging conditions and high rotating speeds was measured. The pressure data on the stator blade were analyzed in the time domain and frequency domain to identify and evaluate the cavitation characteristic. The transient cavitation flow inside the torque converter was also simulated with the computational fluid dynamics model. The results show that the shedding of cavitation seriously reduced the hydraulic performance, hindered the fluid flow, and destroyed the stability of the flow field. Moreover, cavitation aggravates the complexity and nonlinearity of the pressure frequency and hydraulic performance oscillation of the torque converter, and seriously affected the shaft/blade interaction frequency between the pump and stator. Meanwhile, the occurrence and degree of cavitation in the torque converter can be evaluated by APS.shaft/APS.blade (the amplitude ratio of the shaft interaction frequency and blade interaction frequency between pump and stator) with spectrum analysis of the dynamic pressure, and the critical value was 1.6 for the test torque converter. The research revealed the influence of cavitation on the internal flow field of the torque converter and provided a novel practical cavitation evaluation technique.

<div class="htmlview paragraph">This paper presents the theory and experimental performance of a system for detecting engine misfires in automobiles. The method is potentially suitable for meeting the California Air Resources Board (CARB) requirements under On Board Diagnostics II (OBDII) rules.</div> <div class="htmlview paragraph">The instrumentation for the present method measures (noncontacting) crankshaft instantaneous angular speed. Highly efficient signal processing algorithms permit detection of each individual misfire.</div> <div class="htmlview paragraph">The performance of the present method is expressed in terms of error rates made in detecting individual misfires. Normal operating conditions yield error rates under 10<sup>-4</sup>. Under worst case conditions consisting of light load, high RPM and rough roads with the torque converter in lockup are under 10<sup>-3</sup>.</div>

A study of the working fluid flow in the torque converter was carried out using CFD modeling technology and an analysis of the dependence of cavitation on the torque converter operating mode. It is noted that torque converter cavitation mainly occurs at low gear ratios, the degree of cavitation decreases as the gear ratio increases. Most of the cavitation bubbles formed at the ends of the reactor wheel blades, which led to an unstable change in the moment characteristics and a deterioration in the torque converter performance. The analysis showed that the cavitation process is extremely unstable and periodic, and the development of cavitation near the top of the impeller blade occurs in four stages: the creation, growth, separation and decay of cavitation bubbles.

<div class="section abstract"><div class="htmlview paragraph">With the aim of improving engine performance, recent trend of fuel injection nozzle design followed by engineers and researchers is focusing on more efficient fuel break up, atomization, and fuel evaporation. Therefore, it is crucial to characterize the effect of nozzle geometric design on fuel internal flow dynamics and the consequent fuel-air mixture properties. In this study, the internal flow and spray characteristics generated by the practical multi-hole (10 holes) nozzles with different nozzle hole length and hole diameter were investigated in conjunction with a series of computational and experimental methods. Specifically, the Computational Fluid Dynamics (CFD) commercial code was used to predict the internal flow variation inside different nozzle configurations, and the high-speed video observation method was applied to visualize the spray evolution processes under non-evaporating conditions. Moreover, the Laser Absorption Scattering (LAS) method was implemented to explore the spray evaporation characteristics. The different nozzle internal flow properties summarized from the computational results could be used to give a comprehensive explanation for the mechanism behind the spray behaviors observed in the experiments. Furthermore, the nozzle geometrical design effect was correlated with the numerical and experimental results under the evaporating and non-evaporation conditions. It indicated that the hole geometry can alter the dynamic internal flow, liquid jet break up, spray propagation, and the ambient gas entrainment, simultaneously. Moreover, two of the most important factors, hole diameter and hole length, can exert different effect on the spray break up and evaporation process. For the current experiments, an appropriate ratio of nozzle hole length to diameter is found and suggested concerning the fuel break up and evaporating characteristics. When pursuing the optimum nozzle geometrical design, the effect of hole length and hole diameter should be considered from a comprehensive view.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Demands for higher power engines have led to higher pressures in fuel injectors. Internal nozzle flow plays a critical role in the near nozzle flow and subsequent spray pattern. The internal flow becomes more difficult to model when the injector pressure and internal shape make it more prone to cavitation. Two Bosch injectors, proposed for experimental and computational studies under the Engine Combustion Network (namely “Spray C” and “Spray D”) are modeled in the computational fluid dynamics code ANSYS Fluent. Both injectors operate with n-dodecane as fuel at 150 MPa inlet pressures. The computational model includes cavitation effects to characterize any cavitating regions. Including compressibility of both liquid and vapor is found to be critical. Also, due to high velocity gradients and stresses in the nozzle, turbulent viscous energy dissipation is considered along with pressure work resulting from significant pressure changes in the injector. Results are compared against available experimental data and demonstrate that Spray C has a cavitating zone along the nozzle wall whereas Spray D is noncavitating. The influences of fluid compressibility, liquid and vapor property implementations, and inclusion of energy solution are shown to be important for the internal flow as well as nozzle exit flow with direct impact on atomization and spray pattern. Finally, the two injectors are compared to examine the influences of fuel vapor formation due to cavitation on important quantities at the nozzle outlet.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Engineering systems are often too complex and their behavior cannot be determined using closed form or exact methods. To circumvent this problem, numerical methods, such as boundary element method, have been formulated to obtain approximate solutions to partial differential equations, which describe the behavior of the physical engineering systems. However, the inherent uncertainty in constitutive formulation causes uncertainties in the solutions obtained by numerical methods and undermines their validity. Conventional analysis does not account for material uncertainty, which is, however, accounted for in the design phase. This paper addresses the impact of uncertain shear modulus for plane strain linear elasticity problems on the numerical solutions obtained using boundary element method. The uncertainty is modeled using fuzzy approach. Matrix parameterization is developed to obtain exact worst case bounds on the solutions assuming that a correct partial membership function is given. Numerical examples are presented to illustrate the behavior of the method.</div></div>

<div class="htmlview paragraph">Under any driving conditions, the gas flow in present-day monoliths for automotive exhaust catalysts shows laminar characteristics resulting in thick boundary layers. These tend to restrict mass transfer, a highly desirable prerequisite to good catalytic activity.</div> <div class="htmlview paragraph">Based on the theory of catalysis and in the light of such all-important mass transfer, the design of the existing type of catalyst metal supports has been revised.</div> <div class="htmlview paragraph">The new metal supports vary from their predecessors by largely split and slotted honeycomb passages. In this way, gas flow is split and divided over and over again. This results in thin boundary layers and turbulence on the catalytically active support surfaces, with intense mass transfer between the core stream and the surface-contacting zone.</div> <div class="htmlview paragraph">The resultant improvements are discussed in terms of catalytic effect, size, weight, cost, internal flow, temperature equalization and component strength.</div>