A method of designing hypoid gear drives in which transmission errors are robust against misalignment under a loaded state was investigated for the purpose of reducing gear noise caused by the final drive unit of vehicles. The effect of the lengthwise curvature of a hypoid gear on transmission error under load was predicted by using a newly developed tooth contact analysis (TCA) technique. The effect of the lengthwise curvature was also examined by evaluating transmission errors under a loaded state in a machine that had provisions for displacing the pinion and gear in the P, G and E directions. It was confirmed that a face-hobbed gear design makes transmission error robust against displacement error along the pinion axis. An example is shown where transmission error under load was reduced successfully by taking advantage of this transmission error characteristic of facehobbed hypoid gears. Furthermore, this paper proposes a method of designing robust tooth surface modifications on the basis of the Quality Engineering Method. It was confirmed that the proposed method provides a hypoid gear surface that keeps transmission error at a low level under load.

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Presented is a generalized methodology for the integrated design and manufacture of hyperboloidal gear pairs. This methodology is applicable for any gear type where spur, helical, bevel, worm, spiroid, hypoid, and non-circular gears are special cases of a generalized hyperboloidal gear pair. A survey of existing methods for hypoid gear design and manufacture are discussed to illustrate certain deficiencies inherent in present day methods for gear design and manufacture. A brief discussion of cylindroidal coordinates is given along with examples of various gear types to demonstrate the versatility of this special system of curvilinear coordinates for the synthesis of generalized gear pairs. Subsequently, design rating parameters of such generalized hyperboloidal gear elements are included to evaluate candidate gear pairs. These rating parameters include maximum Von Mises fillet stress, tooth surface contact stress, coefficient of friction, flash temperature, lubricant film thickness, and instantaneous tooth mesh losses.

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Since the tooth surfaces of the crossed helical gears have an involute helicoid surface, the production and assembly of the gears are easy compared with other kind of gears. On the other hand, Because the contacting tooth surfaces of crossed helical gears are engaged in a point contact, the load carrying capacity of crossed helical gears is quite limited. Theoretical studies on crossed helical gears have been published [1-5]. Since the engagement of crossed helical gears is dealt with in three-dimensional space, the design formulas for the crossed helical gears become complex. In this study, we developed a new designing method in which shaft angle, reduction ratio and center distance can be arbitrarily set using dual vectors. In addition, using the crossed helical gears designed by our method, tooth contact analysis was carried out to examine the effect of the design conditions of the crossed helical gears on Hertzian pressure between tooth surfaces.

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The approach to synthesis of a gear scheme that meets given specification - overall dimensions, location of input and output shafts, kind of gearing, number of stages, etc. - proposed in this paper develops earlier-developed classification of skew-axis gear schemes. The essence of the approach is that a designer is capable of specifying input data depending on design task. The possibility of doing so is provided by (1) such representation of a gear scheme, that the model contains a set of geometrical parameters of the scheme and its customizable properties - this set is called "the set of signs" ; (2) such model of synthesis process, that a set of gear schemes to be found is obtained as a result of combinatorial search in the set of signs ; (3) development of optimization algorithms which make the base for the model of synthesis. Computer system developed by the authors makes possible visual representation of a gear scheme and tracing of its evolution by changing one or more parameters at a time.

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It is reported that the WN gear has higher load capacity. Windhaven included the idea of the arc teeth perpendicular to the teeth trace in his patent application of WN gear. Maki has proven the validity of the principle of arc teeth perpendicular to the teeth trace by means of vector analysis. This study is related to the design, processing and measurement of the WN helical gear and spiral bevel gear with arc teeth perpendicular to the teeth trace.

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Because of the geometrical limitation of face tooth width, the face-gear drives were applied usually only for low power or motion transmission. In order to extend the application, tooth width design is thus a very important topic for the design of face-gear drive. In this presentation, the authors show a new concept to design the face-gear drive for power transmission by applying nonstandard basic rack and profile shifting. Additionally, an optimal relation of helix angle and offset will be established to get a maximum face width and better mesh performance for hypoid face gear. A new classification and method to calculating the contact ratio of face gear drive are also introduced. Finally, a numerical example will illustrate the mentioned concepts and calculation methods.

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The authors developed cylindrical worm of WN gear Type. Tooth surface of this cylindrical worm is generated by a grinding wheel with two circular arc connected at pitch point, like as Sin marc WN gear. Contact lines of this gearing lies perpendicular to the relative velocity on gear teeth. And very small relative curvature between gear teeth is obtained.

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A new method of tooth surface modification for cylindrical worm gears is proposed. This method can always offer ideal tooth contact and no transmission error regardless of tooth profiles and addendum modification of worm gears. The method is realized by introducing a special hob with non-whole thread numbers and with 1 or 2 flute numbers. The phase difference caused by using the hob with the non-whole thread numbers in hobbing the worm wheel is compensated when the face width of worm wheel just has come in the space of hob flute. Two kinds of worm gear pairs with convex and concave profiles and with positive and negative addendum modifications were designed and made on a basis of the proposed method. Clearances between the meshing teeth of the gear pairs were calculated and compared with that based on the previous tooth surface modification method and also tooth contact tests of the gear pairs were conducted under the loaded conditions. As a result, the desirable contact patterns that almost agree with calculated ones were obtained.

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The high performance of the hourglass worm gearing, especially whose worm teeth are hardened and ground by conical grinder has become widely recognized. But this hourglass worm gearing has next outstanding problems. Namely, (1) The difficulty of the manufacturing of the hob cutter and maintenance of its accuracy. (2) The poor cutting ability of the hourglass worm teeth. Therefore we propose new methods to solve these problems. Namely, (1) Grinding method for worm wheel teeth by electro-deposited diamond wheels. (2) Generation for worm teeth by Mach type cutter. We actually manufactured new hourglass worm gear set by these new methods of manufacturing. And also we tested new hourglass worm gear reducer with these gear set and proved its high performance.

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Direct Digital Simulation (DDS) method is proposed for geometrical calculation of gear tooth surfaces. It was successfully used for tooth form calculation of the following gears : spiral bevel, hypoid, spiroid, hyperbolic, helical, Wildhaber-Novikov, double enveloping worm, globoid, worm, crown gears and for variable ratio rack. The following DDS software options were tested : tooth geometry, digital master gear, contact pattern, 3D visualization, 3D contact animation, contact stress, gear misalignments, transmission error, export gear geometry in to 3D CAD files, sliding and rolling velocities, gear tooth cutting and grinding, not involute tooth profiles.

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The double looped planetary gear system (DLPS) is composed with two sets of the single looped planetary gear system (SLPS) that includes a planetary gear mechanism and a continuously variable transmission (CVT). Depending on occupied position of CVT inside DLPS, DLPS is divided to two types : exclusive CVT and inclusive CVT type. DLPS is possible to control output speed sensitively by CVT. and usable for a transmission of hybrid vehicles. Because DLPS has two loop circuits from the topological point of view, various types of power flow appear in the circuit. This paper deals with classification of the power flow type of DLPS. At first, the author introduces the characteristic diagram regarding to angular velocity of planetary gear mechanism, that explains classification of power flow of SLPS and speed variation range induced by CVT operation. Secondly considering dividing condition of power flow in a planetary gear mechanism, he intends to apply the diagram to DLPS and presents an extended diagram that shows combination of power flow of SLPS. Moreover, following explanation about the extended diagram, he presents a table showing whole type of power flow of DLPS. Finally a practical example of DLPS and its power flow are explained.

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This paper describes a fundamental geometric relationship between pitch curves and tooth profiles in the spur gearing with variable ratio. The author derives a simple algebraic form of the extended Euler-Savary's equation, which describes a relationship between radii of pitch curves and radii of curvatures of tooth profiles in this gearing, with elementary geometry. This formula is based on the Willard Gibbs' dissertation. Here, a slope of common tangent of pitch curves at the pitch point to the center line of gearing is mainly considered independently of curvatures of pitch curves. Further, the author derives an analogical formula considering a role of the curvature of pitch curves and indicates that it yields to the ordinary Euler-Savary's equation in spur gearing with constant ratio. Finally, an application of these formulae to elliptical gearing is presented.

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In this study, a simple method of numerical analysis to obtain particularly the local characteristics of the surfaces of machine elements processed by straight-lined tools is presented. In addition, as examples of the application of this method, the measurement, the error analysis and the measured results using a three-dimensional measuring machine are reported for the tooth surface of a Hindley hourglass worm. Furthermore, we also report that the local characteristics of the two tooth surfaces obtained by our numerical analysis explain the analytical and experimental results of the tooth contact fairly well.

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A computerized approach is proposed for designing the optimium tooth-surfaces which provide the favorable tooth bearing contact and motion transmission in axis-displaced crossed helical involute gears. The approach is applied to a few kinds of axis-displaced gears by way of example, and the optimum tooth-surfaces are obtained. The tooth contact performances such as tooth bearing contact and motion transmission of the testing gears having the optimum tooth-surfaces, are calculated and evaluated by utilizing newly developed tooth contact analysis program. From the results, it is clarified that the proposed approach is effective for the above-mentioned purpose. And also, it is ascertained this approach is applicable for all types of cylindrical involute gears.

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The problem of gear noise, particularly in motor vehicles, has become an important and annoying problem due to the continual reduction in sounds from other noise exciters such as engines and wind noise. In an effort to control gear noise, one must first select the proper design and profile modifications to optimize a design. Once this is done, it typically becomes difficult to economically manufacture the gears with their optimized modifications. One goal is to select designs that have a low sensitivity to manufacturing errors, thus allowing a much lower statistical spread in the noise levels of the transmission. In this paper, we present two procedures for identifying the sensitivity of a gear pair to manufacturing errors such that individual gear designs may be compared to one another in an effort to achieve low manufacturing sensitivity.

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One of the most important performances which a pair of tooth surfaces of gears for power transmission must have is smooth and quiet transmission of the torque. However, the present designing methods of gears consist of different coordinate systems, nomenclatures and calculation methods according to kinds of gears and cannot choose the tooth surfaces to satisfy such dynamic requirements as "no variation of bearing loads". To solve these problems, a unified designing method applicable to all kinds of gears for power transmission is presented, which has the same equations defined in the common coordinate systems which are determined by the disposition of the gear axes and the angular velocities and can deal with the dynamic requirements. An automobile hypoid gear pair with involute helicoids for pinion and the conjugate surfaces for gear is shown as an example of this unified method.

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Under the considerations that many power transmission gears run practically in one rotational direction, the dimensions of the front side (loaded side) and backside (unloaded side) of the tooth might be designed individually. In this research, a new kind of involute gear was developed, where the standard pressure angles of the front side and backside of the tooth were different. The maximum tensile tooth fillet stress was calculated by two-dimensional FEM. Increasing the standard pressure angle of the backside of the tooth from 20deg to 35 deg decreases the maximum tensile tooth fillet stress about 20% and increased the stiffness of tooth due to the increased critical section. Bending fatigue tests were performed for two types of normalized and induction-hardened gears to evaluate the enhancement in bending load carrying capacity using different backside standard pressure angle. The pressure angles of the front side/backside of the tooth of test gears were 20/20deg and 20/30deg. The fatigue test results confirmed the significant increase in bending load capacity by the use of a larger backside pressure angle of the tooth.

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The effect of rotational speed (centrifugal force) on gear crack propagation direction was explored. Gears were analyzed using finite element analysis and linear elastic fracture mechanics. The analysis was validated with crack propagation experiments performed in a spur gear fatigue rig. The effects of speed, rim thickness, and initial crack location on gear crack propagation direction were investigated. Crack paths from the finite element method correlated well with those deduced from gear experiments. For the test gear with a backup ratio (rim thickness divided by tooth height) of m_b=0.5, cracks initiating in the tooth fillet propagated to rim fractures when run at a speed of 10,000 rpm and became tooth fractures for speeds slower than 10,000 rpm for both the experiments and analysis. From additional analysis, speed had little effect on crack propagation direction except when initial crack locations were near the tooth/rim fracture transition point for a given backup ratio. When at that point, higher speeds tended to promote rim fracture while lower speeds (or neglecting centrifugal force) produced tooth fractures.

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The paper regards a particular gearing and reports determination of the magnitude and time of applying the starting load of a gear. The authors point out that those load characteristics are important components of the gear load histogram. The calculations consider three basic mechanical characteristics of the working machine : crane, calander and ventilator ones. The results found are given in a form convenient for practical application.

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This paper describes the analytical method for calculating contact stresses in spur, helical and bebel gears using the boundary element method. Since, in many old studies based on the three dimensional finite element analysis, the elasto-static singularity of contact line is not adequately taken into account, exact analytic expression must be derived for the computation of stress distribution along the instant narrow strip zone of contact with infinitesimal width. In this paper, the author presents a convenient and practical way of calculating the load distribution along the contact line of gear teeth by applying the boundary element technique. The advantage in applying the boundary element method to the contact problem of meshing gears is to easily take the direct relationship between tooth stiffness and tooth surface contact load.

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Base oil type, oil viscosity, additive type and content have a strong influence on typical gear failures. As it is not possible to quantify the lubricant influence on load carrying capacity simply from the knowledge of physical or chemical oil data many test methods were developed for the evaluation of mechanical-technological lubricant properties. Simple low-cost bench test methods often show poor correlation with practice. From experience and systematic investigations it can be shown that testing of gear lubricants can adequately be performed only in gear test rigs using specified test gear geometry. In continuous work over many years the standard FZG back-to-back gear test rig was developed and improved for different types of gear failure simulation. The standard FZG oil test A/8, 3/90 is widely used for the evaluation of the scuffing properties of industrial gear oils. Automotive gear oils of GL4 level can be tested in the step test A10/16.6R/90, axle oils of GL5 level in the shock test S-A10/16.6R/90. For the slow speed regime the wear test C/0.05/90 : 120/12 can be applied. The influence of lubricants on the micropitting performance of gears can be evaluated in the micropitting test GF-C/8, 3/90. Different pitting tests are available as single stage tests PT-C/9 : 10/90 or load spectrum tests PT-C/LLS : HLS/90. A universal test PITS Ci85 TS combining pitting and oil ageing performance was developed. The results of such tests can be introduced as "strength values" for the lubricant into load carrying capacity rating methods.

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Grease lubrication hypoid gear motor has been requesting to realize universal mountings. Hypoid gear is apt to arise scoring failure on tooth surfaces. Then, hypoid gear temperature rise was measured by using complete grease lubricated gear motor that was composed of two-stage reduction, in which high-speed stage was hypoid gear pair and low stage helical gear. Hypoid pinion was manufactured on motor shaft end. Motor rating was 0.75kW and rotation speed 1800r/min. Hypoid gear dimensions were tooth number 4 and 39 of driver and follower respectively, pinion offset 15mm, carbonized heat treatment. Lubricants were NLGI 000 alicyclic urea grease, NLGI 00 lithium soap grease, and ISO VG 200 hypoid gear oil to clarify characteristics of grease lubrication. Maximum temperature rise of grease lubrication was 73.4K at hypoid gear tip. Temperature rise ratio of grease to hypoid gear oil was nearly 1.2 for NLGI 000 grease, however varied from 0.9 to 1.7 for NLGI 00 grease. Right angle hypoid-helical gear motors of rating 0.1 to 2.2kW lubricated by NLGI 000 alicyclic urea grease were finally developed and now are on the market.

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Sliding resistance in gear teeth can have a dominant effect on housing vibration, noise and efficiency. One of the parameters that greatly influence the friction under certain running conditions is surface roughness. In this work, rough friction was measured in lubricated sliding of roller surfaces. By examining 3D surface topography of two mating bodies, both surface roughness and its interaction between contacts were studied. For this purpose, a rough-friction test rig was designed and constructed. In this rig the contact pressure between two rollers can be varied while controlling the sliding speed. The input / output torques and forces can be measured simultaneously. Rollers that were manufactured to simulate the real gear surfaces were examined by a 3D stylus profilometer (resolution 4 nm). Results are expressed in terms of Stribeck curves (friction coefficient as the function of Hersey parameter [ηv/p]). The results showed good agreement with current theory.

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Friction and wear of transmission interface are key ways of energy consumption and transmission mechanism failure. Economic losses caused by friction and wear of transmission interface are astonishing. Gear transmission is the most common mechanism of power and motion transfer. Improvement of antiwear and friction-reducing capacities of gear surface has therefore become one of the most interested research topics in tribological cycle. In recent years, in our studies of interdisciplinary transmission tribology and transmission tribology design, a new idea of on-line strengthening of gear surface has been proposed, some achievements have also been made.

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The study of friction loss of spur gears was carried out, using test gears with a center distance a=183 mm. The range of circumferential velocity was extended up to about 120 m/s. Generally speaking, the author obtained that, the higher the lubricating oil viscosity, the lower the friction loss. Further he found that a most suitable oil viscosity in order to reduce the friction loss exists for the gear unit, including not only the test gears but also the bearings and the gear box. As far as tooth form is concerned, the cutter pressure angle α_0=25° gives the lowest friction loss for the gear unit.

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The plastic gear is used for turn and power transmission. The abrasion and damage of the tooth of plastic gears has become a problem. In addition, in the use of the plastic gear, it is the problem of strength evaluation of teeth. There is two thinks on the strength of the tooth. It is a breakage with the progress of the abrasion of the tooth in other. This paper deals with the result of tooth damage in evaluation of a molded plastic gear. Injury to a tooth is classified largely in two groups, one is progress damage and other is final damage. [1-6] In addition, abrasion and breakage of the tooth were analyzed through theory and experiment, and abrasion and evaluation of the breakage were carried out. The abrasion of the tooth was considered as following. The relationship between stress of Hertzian contact, circumference speed of the tooth, running time and abrasion weight was clarified. It was possible to obtain the precious material for design and use of molded plastic gear from the result in this study.

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The plastic gears, made of the low fractional materials or emploied the grease, break by the bending stress. Since the larger bending deflection with transmitted power the larger real contact ratios of plastic gears, the bending stress calculation formulae of the metalic gears don't be able to apply for the plastic gears. As the studies of the Prof. Yelle's works, the pulsating impact fatigue S-N curves of cantilevers, the impact fatigue lives of quasistatic gears and the power circulation test using PA66, POM, PA66-PE alloy and the pair of PA/POM gears, a practical formula corresponded the ISO standard is proposed by the introducing of the load distribution factor, the thermal effect factor and the molding fault factor.

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The plastic gear is effective from the viewpoint of the productivity for the comparatively small gear. Generally, the plastic gear is made by the injection molding of the crystal resin. In the case of the injection molding plastic gear, the deformed layer nearby the surface of tooth is softer than the core structure. Authors noticed that the sound level of the two plastic gears engaged was low while a skin layer and an intermediate one existed. It is expected that the noise level is kept low by positively forming deformed layer with some extent thickness. In this paper, the formation mechanism of the deformed layer in the injection molding plastic gear is studied. FEM is used to perform the thermal analysis of the cooling process of the resin filled in the mold. According to the analytical results, the cooling rate of melting polymer of the near-wall region as well as the case of the product of metal amorphous alloy was very rapid. The relationship between the manufacturing conditions and the deformed layer for the injection molding gear was estimated

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In this study, we investigated the properties of noise and vibration for a pair of gears engaged a nylon gear with a steel gear. On the basis of experimental results, we considered about the noise generation mechanism. It becomes clear as follows. The plastic gear is excited vibration heavily and the noise is radiated loudly from the plastic gear rather than the mating steel gear. The vibration of plastic gear is caused by the flexibleness of plastic gear tooth and the lateral vibration of plastic gear influences the noise radiation directly. It is considered that one of the practical ways to reduce the noise of plastic gear is to reduce the noise radiation from the plastic gears by decrease in lateral vibration.

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Exact analytical solutions of transmission errors with eccentricities of involute cylindrical gears are proposed. Analytical equations to obtain transmission errors with eccentricities are derived shortly. The influence of the center distance errors, the ratio of eccentricities and phase differences is investigated under no load. In addition, transmission errors including eccentricities of a pair of spur gear are measured under no loading condition. The results show that the measured and calculated transmission errors agree with each other and the analysis is verified accurately. The influence of center distance errors is so little as to be neglected comparing to the amount of transmission errors. The sum of eccentricities is related to the peak-to-valley value of transmission errors and the ratio of eccentricities is related to waveforms of transmission error curves. Phase difference of eccentricities has a little influence on transmission errors, but it is not negligible comparing to the amount of transmission error caused by tooth flank topography and tooth deflections. For further applications, the analysis can be used to remove waviness from transmission error curves as the filtering technique.

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A scanning measurement of face milled, face hobbed, formate or generate hypoid gear is developed, and the concept of conjugate surface and composite error used in the measurement is introduced. A method of simulating tooth contact pattern and transmission error of hypoid gears based upon machine setting and actual tooth surface measurement data is discussed. The result of the simulation is compared with the experimental data, and the effectiveness of the measurement of tooth flank form of hypoid gears is discussed in a case of wear trouble experienced actual mass production gears.

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A reference tooth flank has been used in the previous interferometry measurement of form deviation of gear tooth flank. In this investigation, new measuring method by an accurately ground plate instead of the reference tooth flank is proposed. The use of this reference plate incorporated makes cost, time and labour of manufacture of the reference tooth flank decrease.

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In 1949, the first engine dynamometer was installed at Southwest Research Institute (SwRI), thereby initiating an automotive research program that today exceeds $100 million USD in annual revenues. This program has grown to include virtually all things automotive. One of the fastest growing areas of automotive research at SwRI is in transmission design. Great advances have been made in automotive transmission design, yet there is still much room for improvement. The current production, multi speed manual transmission, used in automotive applications represents a very mature technology. A typical transmission consists of a dual shaft configuration, containing five pairs of gears in rotating contact with each other through which various load paths are selected. Supporting this system is a multiplicity of bearing sizes, types and locations. The challenge to the transmission designer is to provide a system that can provide high efficiency across a wide range of operating speeds and torque, under continually changing conditions. Yet based upon dynamometer test results, efficiency values for transmissions used in similar sized vehicles, but produced by different manufacturers, have been found to vary greatly. This paper will provide efficiency trends and values associated with current production manual transmissions and how they are affected by mounting angle and operating temperatures. Areas in which improvements to efficiency can be realized will be discussed including lubrication, windage, bearings, supports, and gear tooth modifications.

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This paper is identifying tendencies of future development of the gears and of general use and special geared transmissions. Tendencies are estimated on the basis of top research ideas, tendencies of technology and "state of the art" achievements in companies specialised in mechanical transmissions. At cylindrical gears : technological method application for fitting within the ME class [DIN] of the admissible stress diagrams ; topological corrections, high toothing gears with integer contact ratio, re-launching non-involute gears in the new technological background offered by the possibility of grinding and checking any profiles. At worm gears : numerically controlled contact localising using 3-4 optimising parameters, double-enveloping worm gears with grindable worm by means of an internal mobility procedure. Also the paper identifies possible development tendencies of gear transmissions : general use speed reducers, custom-made gearboxes (for power plants, mining, ships, cement industry), special multipliers, geared motors, variable speed transmissions, drives for robots and machine tools.

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The number of tooth profile measuring instruments takes 65% of total number of gear measuring instruments developed since early the 20th century. This means the accuracy of tooth profile most greatly affects gear performance among all of the gear items. This paper describes the change of gear measuring instruments in the world, from mechanical type to CNC type machine. Aiming at the high-speed and high accurate measurement, ultimate measuring method such as "free from the influence of room temperature", "rough centering" and "output of measured deviation based on the gear functional center axis" are proposed. Optical checker to measure whole of the tooth flank at one time is another target of development for the future. In the 21st century, some methods should be established internationally in common to certify the accuracy of profile form measuring instrument. This will be realized by the means of reference master artefact. To certify the accuracy of such reference master, the importance of development of the device and method for this is emphasized.

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Every long-range prognosis in the area of engineering development (politics, sociology, economy etc.) is essentially wrong. They had promised us (nearly with hundred-percent certainty at Neil Armstrong moon walking time) that people would have built permanent basis on the moon and human foot would have stood on Mars, people would have ordinarily traveled by their personal hovercrafts for their buying and entertainment. And where the reality is? But on the other hand nobody had foreseen so powerful growth of computers, Internet, e-mail and GSM telephony. In short - the only respectable prognosticator in the area of engineering development was Jules Verne. Therefore here is not possible to perform the full prediction of gear transmissions development in this article. But after the short recapitulation of interesting present-day and historic evolutionary steps the article tries to outline one next, evidently necessary, evolutionary step in the area of gear transmissions.

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A state-of-the-art contact mechanics model of a planetary gear set is employed to study the effect of a number of manufacturing and assembly related carrier and gear errors on the load sharing amongst the planets. Three different groups of errors are considered : (i) time-invariant, assembly-independent errors such as carrier planet pin hole position errors, (ii) time-invariant, assembly-dependent errors such as planet tooth thickness errors, and (iii) time-varying, assembly-dependent errors such as gear run-out errors. With such errors present, planet load sharing characteristics of an n-planet system (n = 3 to 6) is investigated for different piloting configurations under both static and dynamic conditions. Load sharing behavior as a function of key manufacturing errors is quantified and design guidelines are proposed for better planet load sharing behavior.

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So-called "thrust cones" are currently being used in highspeed, single helical spur gear drives for taking up axial forces. To date, thrust cone technology has not been used in vehicle transmissions. To reduce noise emissions in heavy commercial vehicles, the planetary gear set had to be changed from straight to helical-cut gearing. Both single and double acting thrust cones have been developed to take up axial forces in the available installation space. Due to the special conditions, vehicle transmission applications differ greatly from those for stationary transmissions. While stationary transmission thrust cones in the EHD range must only run free of wear, in vehicle transmissions, it is also important to take into account the additional factors of fatigue lifetime, scuffing resistance and risk of wear. The thrust cone performance limits were determined under near-series conditions on a specially-designed gear load test bench. Suitable calculations procedures were then developed. From specification to production, the total development stage was approx. 2 years. Helical-cut planetary gear sets using thrust cone technology have been used as standard since mid 1996 and have proven to be very effective. A noise reduction of approx. 10 to 15dB has been achieved by changing from straight to helical-cut gearing.

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The design and development of a gear unit with variable speed fluid coupling (YTZ50/30) is mainly introduced in the paper. This kind of power transmission device combines a variable speed fluid coupling and an increasing gear unit in the sane case. Limited by the space and some special requirements from the user, the device had to be designed very different from traditional standard one. Some new design concept and new structure is employed in the new device. Such as, the front variable speed fluid coupling and rear double helical increasing gear are used in this power transmission unit, and some new technologies and process are also carried out. Both excellent variable speed performance and the saving energy capacity of this kind of device have been verified by the bench test in laboratory, field adjustment running and then the running in workshop respectively. Since its low cost and high-performance, this kind of power transmission and infinitely variable speed unit can be widely used in various air-blowers, pumps, iron-steel plants, power stations conveyors, ships and so on. Obviously, it will play a very important role not only in saving energy, but also in improving the technological process of the whole power system.

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Multi-body synchronizer and selector mechanism model has been developed and experimentally validated to improve gearshift quality in manual transmissions. The model has been implemented in a commercial multibody program (ADAMS), and it includes simulation of detent mechanism, contact forces on the sleeve, blocker and engagement teeth, as well as jamming on the synchronizer rings. Single, double or triple cone synchronizers can be modeled. The whole selector mechanism from the fork acting on the sleeve to the lever is modeled, including bowden cable. Extensive experimental vehicle and bench tests have been performed to validate the model. To overcome the problem due to the variability of the force and velocity applied by the driver, a dedicated system has been used in bench test rig, where hydraulic force actuator gives repeatable and constant input directly into gearbox. Displacements and axial forces acting on sleeves have been measured on the "Manual Transmission Shiftability Bench". Comparison between numerical results and experimental measures shows good agreement after a preliminary work aimed to rate a number of model parameters (equivalent cone friction, contact stiffness and damping) whose values are not easily available. The model gives a good understanding of gearshift problems, such as double bump and jamming on synchronizer rings, allowing to investigate many potential solutions. Design parameter analysis have been performed for gearshift quality improvement, such as reduction of synchronization effort and duration, and minimization of engagement force (double bump effort). Proposed solutions for multi-cone synchronizer and internal selector mechanism have to be successively tested on the bench. The paper describes the main features of the model together with a discussion on the numerical and experimental results, and new proposals to improve gearshift quality in manual transmissions.

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