Planetary Gear Fatigue Behavior in Automatic Transmission

<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>

The instantaneous efficiency of an epicyclic gear rotary actuator is an important factor in sizing flight control systems where compound epicyclic gear trains are typically used. The efficiency variation can be smooth or fluctuating depending on the combination and timing of the teeth of ring, planet, and sun gears. In this paper, the instantaneous efficiency characteristics of synchronous and nonsynchronous actuators under forward-driving with opposing load and reverse-driving with aiding load are investigated. The emphasis will be on instantaneous, rather than average efficiency of gears. Several gear arrangements are considered: external and internal gears, simple planetary gears and compound planetary gears. Efficiency will be discussed considering not only the geometry of the mating gears, but also the relative phasing of the planet gears relative to the sun and ring gears. Synchronous compound epicyclic gears are shown to have large fluctuation in their instantaneous efficiency. When reverse-driving efficiency falls below 0%, the unit cannot be back-driven and will chatter. Nonsynchronous compound gears have a smaller variation in instantaneous efficiency. However, extra care must be taken in timing the compound planet gears, as well as clocking position of compound planet gears relative to ring gears and the sun gear.

<div class="htmlview paragraph">One of the barriers to successful implementation of the continuous slip torque converter clutch (CSTCC) design for automatic transmissions (AT) is transmission shudder. An important factor contributing to shudder is the frictional characteristics of the automatic transmission fluid (ATF). In this paper, we report the development of a test that allows the precise measurement of the frictional characteristics of the ATF at different sliding speeds (μ-v data) using an SAE No. 2 friction machine. A conventional SAE No. 2 machine was modified, by installing a DC static drive motor, to simulate the sliding speeds, surface pressures, and fluid temperatures found in actual vehicle operating conditions. The μ-v data obtained with the machine showed good correlation with the vehicle shudder, i.e., the ATFs showing more negative gradient in the μ-v data caused more severe shudder in the vehicle. Initial shudder and anti-shudder durability evaluations were conducted using a variety of commercial and experimental ATFs. It was found that the highly friction-modified ATFs exhibited good initial anti-shudder performance. ATFs meeting major North American OEM requirements were not always acceptable for CSTCC applications.</div>

<div class="section abstract"><div class="htmlview paragraph">Reducing loss torque in automatic transmissions (ATs) is a key factor in improving fuel economy. A promising approach is to reduce the viscosity of the Automatic Transmission Fluid (ATF) so as to minimize churning loss. Aisin AW and JXTG Nippon Oil & Energy Corporation have developed a super low viscosity ATF, called “AW-2”, which has approximately 50% lower kinematic viscosity at 40 °C compared to the conventional ATF “AW-1”. It is generally understood that if the viscosity of an ATF is too low, it can have a negative impact on the fatigue life of components such as gears and bearings, and possibly lead to increased wear or seizure. AW-2 was designed to solve these problems via the application of two key technologies. The first is a high performance base oil with a low traction coefficient, which translates to low viscosity under high pressure conditions. This decreases the shear resistance between sliding surfaces under elastohydrodynamic lubrication (EHL) conditions, which contributes in improving the fatigue life of bearings and other components. The second is an ester type base oil with high polarity. It was found that the amount of ester base oil used has a major influence on fatigue life. The adsorption of esters onto metal surfaces is thought to improve lubricity in severe lubrication conditions. Durability tests were performed in a wide range of conditions, using gear and bearing components and actual transmission units, and it was confirmed that AW-2 outperforms AW-1, despite its super low viscosity. Furthermore, AW-2 reduced loss torque in the transmission by approximately 10% compared to AW-1.</div></div>

<div class="htmlview paragraph">A new point of view in automatic transmission is proposed by R-R chart, which is a new analytic method based on the linearity of planetary gear and gear shift mechanism. The R-R chart is a visual tool to describe the whole motion of each rotational element of planetary gears in relation to the gear shift mechanism. Therefore, anyone can easily find on R-R chart not only the substance of the gear shift mechanisms in present automatic transmissions but also new gear shift mechanisms for the future automatic transmissions. This paper shows that the R-R chart is unique in 4-speed automatic transmissions with fixed compound planetary gear sets. As a result of the R-R chart application, this paper classifies the fixed compound planetary gear sets with 4 elements into 12 sets and the gear shift mechanisms into 3 types. Also, 4 R-R characteristic equations are derived as a correlation between speed ratios in 4-speed automatic transmissions. This paper describes systematically the gear shift mechanisms for 5- and 6-speed automatic transmission by R-R chart. Finally, this paper introduces the new gear shift mechanism for 5-speed automatic transmission with 3 clutches and 1 brake.</div>

<div class="htmlview paragraph">The rheological behavior of automatic transmission fluids (ATF) ranges from moderately shear-thinning to Newtonian. However, no commercially available ATFs are known to display shear-thickening behavior. A theoretical investigation was performed to determine if any advantages could be derived from the use of shear-thickening ATF in automatic transmission components and subsystems. A series of theoretical shear-thickening, shear-thinning, and Newtonian fluids were modeled by a power law function and compared to a reference shear-thinning ATF in simplified representations of transmission components and subsystem geometries. The results indicate that a shear-thickening ATF with zero shear viscosity, infinite shear viscosity, and power of 417 mPa-s, 6.23 mPa-s, and 1.03(dimensionless), respectively, displays optimized behavior with respect to the reference shear-thinning ATF.</div>

<div class="htmlview paragraph">Significant changes are occurring in the development of automatic transmission fluids (ATF) which impact the selection of both additive components and lubricant base oils. In particular, the need for improved viscometrics at high and low temperatures, combined with the need for increased oxidation performance and shear stability are moving formulators towards use of higher quality API Group II (100 - 120 VI) and/or Group III base oils.</div> <div class="htmlview paragraph">Several benefits are apparent with the use of API Group III base oils in ATF. Their naturally high Viscosity Index of >120 provides opportunities to use a higher base oil viscosity compared to API Group I and in many instances Group II base oils. This reduces the amount of Viscosity Modifier in the finished ATF and improves overall shear stability. Higher kinematic viscosity also improves volatility which leads to improved oxidation resistance.</div> <div class="htmlview paragraph">Low temperature fluidity can be improved by modifying the amount and type of residual wax in the base oil. This is achieved through two main factors, namely: (i) feed selection and (ii) the type of dewaxing process, isodewaxing being preferred to conventional solvent dewaxing. Finally, the higher concentration of saturated versus aromatic molecules in an API Group II and Group III base oil provide enhanced antioxidant response.</div> <div class="htmlview paragraph">The relationship between base oil composition and ATF performance will be discussed in terms of low temperature Brookfield viscosity, shear stability and oxidation performance. Particular emphasis will be given to API Group II+ and Group III base oils produced by severe hydro-treating and isodewaxing.</div>

<div class="htmlview paragraph">In recent years, progress has been made in reducing the viscosities of manual transmission fluids (MTFs) and automatic transmission fluids (ATFs). Lower viscosities of MTFs and ATFs are expected to improve the fuel economy of automobiles by reducing the viscous resistance. Examples of low-viscosity ATFs already commercially available include Toyota Auto Fluid WS and ZF Friedrichshafen AG's ZNF 13014. This paper first reports methods for measuring the torque transmission efficiency in manual and automatic transmissions. We explain a simple rig test that we developed using an IAE gear test machine, and we describe oil temperature increase tests and torque measurement tests using actual transmissions and fuel economy tests using actual vehicles. Next, we describe the effects of lower viscosities on the torque transfer efficiency as measured with these measurement methods. Because lower viscosities are likely to worsen the wear resistance, extreme-pressure performance, and fatigue resistance of MTFs and ATFs, we studied the effect of the base oil composition and the molecular structure of PMA-based viscosity index improvers (VIIs) on the oil film thickness. We were able to determine by three methods that the film thickness of low viscosity lubricant could be made greater than that of conventional lubricant. The oil film was made thicker in the first method by increasing the molecular weight distribution of the base oil, in the second method by reducing the molecular weight of the PMA-based VIIs, and in the third method by changing the alkyl groups of the polymethacrylate-based (PMA-based) VIIs. The results of our study showed that our optimized lower-viscosity MTF, when evaluated in terms of its wear prevention, extreme-pressure properties, and fatigue prevention, has equal or better performance in each area in comparison with MTFs with conventional viscosities.</div>

Planetary gears are widely used in the industry due to their advantages of compactness, high power-to-weight ratios, high efficiency, and so on. However, planetary gears such as that in wind turbine transmissions always operate under dynamic conditions with internal and external load fluctuations, which accelerate the occurrence of gear failures, such as tooth crack, pitting, spalling, wear, scoring, scuffing, etc. As one of these failure modes, gear tooth crack at the tooth root due to tooth bending fatigue or excessive load is investigated; how it influences the dynamic features of planetary gear system is studied. The applied tooth root crack model can simulate the propagation process of the crack along tooth width and crack depth. With this approach, the mesh stiffness of gear pairs in mesh is obtained and incorporated into a planetary gear dynamic model to investigate the effects of the tooth root crack on the planetary gear dynamic responses. Tooth root cracks on the sun gear and on the planet gear are considered, respectively, with different crack sizes and inclination angles. Finally, analysis regarding the influence of tooth root crack on the dynamic responses of the planetary gear system is performed in time and frequency domains, respectively. Moreover, the differences in the dynamic features of the planetary gear between the cases that tooth root crack on the sun gear and on the planet gear are found.

<div class="htmlview paragraph">An additive package for the automatic transmission fluid (ATF) used in slip lockup control automatic transmissions has been developed that satisfies all the requirements of the DEXRON<sup>®</sup> III, MERCON<sup>®</sup> and JASO M315 specifications. The influence of the base oil and viscosity index improver that are combined with this additive package was also investigated with respect to ATF performance.</div>

<div class="section abstract"> <div class="htmlview paragraph">This SAE Standard covers hose intended for use with automatic transmission cooling system applications. Type A hoses are intended for original equipment or replacement applications while Type B hoses are intended for aftermarket auxiliary cooler applications only. The reference fluid for tests requiring the use of automatic transmission fluid (ATF) shall be Dexron III / Mercon 5 or equivalent ATF that is agreed to by hose manufacturer and customer.</div> </div>

<div class="htmlview paragraph">Friction modifiers have been around for many years. Originally, the application was for limited slip gear oils, automatic transmission fluids and multipurpose tractor fluids.</div> <div class="htmlview paragraph">Since fuel economy became an international issue, initially to reduce crude oil consumption, friction modifiers have been introduced into automotive crankcase lubricants as well. The current emphasis is to improve the fuel efficiency through the engine lubricant and to reduce emissions to the environment.</div> <div class="htmlview paragraph">This paper describes the chemistry of the various organic friction modifiers as well as the non-organic types. A basic understanding is given on the mechanisms how and why these products work as friction modifiers and what is known about structure - activity relationships.</div> <div class="htmlview paragraph">Definitions are given about the various lubrication regimes as well as figures to what extend these regimes are present in current engine tests measuring fuel economy. In addition, it is described which type of friction modifiers is most active in the various lubrication regimes.</div> <div class="htmlview paragraph">Factors influencing the friction reducing properties, like base fluid characteristics and competing additives, are covered and appropriate tests to measure frictional properties are described. Finally, some recent work regarding the effect of some friction modifiers on frictional levels, determined with a pin-on-ring tribometer, is shown.</div>

PurposeIrregular windy loads are loaded for a wind turbine. This paper aims to determine the form of gear failure and the working life of the gear system by assessing the dynamic strength of gears and dynamic stress distribution.Design/methodology/approachThe helical planetary gear system of the wind turbine growth rate gearbox was investigated, and while a variety of clearance and friction gear meshing processes were considered in the planetary gear system, a finite element model was built based on the contact–impact dynamics theory, solved using the explicit algorithm. The impact stress of the sun gear of the planetary gear system was calculated under different loads. An integrated planetary gear meshing stiffness, and the error of system dynamic transmission error were investigated when the planetary gear meshes with the sun or ring gears.FindingsThe load has little effect on the sun gear of the impact stress which was known. The varying stiffness is different while the planetary gear meshes with the sun and ring gears. There were differences between the planetary gear system and the planetary gear, and with load, the planetary gear transmission error decreases.Originality/valueThis study will provide basis knowledge for the planetary gear system.

In this work, bearing outer ring creep in the planetary gear of a gear wind turbine gearbox is investigated. So far, gear creep has only been investigated experimentally on very small bearings under simplified load conditions. This paper presents experimental measurement results from a full-size 2.75 MW wind turbine. The test were performed on a system test bench capable of applying loads in all six degrees of freedom at the rotor hub. The objectives of this investigation are to provoke and measure bearing outer ring creep and to identify correlations to the gear load distributions acting on the planetary gear. After a motivation, a literature overview on bearing ring creep is given. Influences on and occurrences of ring creep are described and the two mechanisms roller-induced creep and gear creep explained. Then, the test setup and the evaluated experiments are presented. The influence of torque, rotational speed and additional non-torque loads on gear load distribution and bearing outer ring creep is shown, discussed and put in relation to findings from literature. Key findings are that outer ring creep speed increases with global rotational speed and torque. Also, gear creep – acting in the opposite direction of roller-induced creep – was found at the generator-sided bearing ring for loads below 40% nominal torque. The planet gear load distributions with sun and ring gear were highly uneven and opposed to each other at low torques while leveling out at high torques due to the load-dependent deformations of sun gear, planet carrier and ring gear. The average gear load distribution over all ring gear positions showed to be influenced only by torque and to be independent of non-torque loads. In accordance, even extreme non-torque loads were found to not influence the creep behavior of the two planetary bearing outer rings.

<div class="htmlview paragraph">Past experience indicates that the method for evaluating the foaming tendencies of automatic transmission fluids, shown in the “Specification for Automatic Transmission Fluid, Type A, Suffix A,” is adequate for the qualification of fluids for transmission operation. Its usefulness, however, for evaluating field failures and for monitoring the shelf-life stability of the foam inhibitor is severely limited by the fact that the procedure requires a sample size of at least 6 qt.</div> <div class="htmlview paragraph">The purpose of this paper is to present a new test procedure for the evaluation of foaming tendencies that utilizes a small sample size (500 ml) and shows good correlation with the results obtained during qualification.</div> <div class="htmlview paragraph">The paper also presents the results of studies which were necessary for the development of the proposed test procedure. These studies were concerned with the mechanism of foam formation and collapse, with the conditions affecting the equilibrium between the rates of formation and collapse, with air entrainment and retention in the fluid, and with the effect of siloxane additives on the foaming characteristics of the fluids.</div>