Automotive Automatic Transmissions Research Articles

Design of automotive mechanical automatic transmission system based on torsional vibration reduction

Automatic transmission system is the core part of vehicle transmission processing, which can improve driving safety. In order to improve the shift effect of automotive automatic mechanical transmission and narrow the gap between the vehicle speed and the expected speed, an automotive automatic mechanical transmission system based on torsional damping was designed in the experiment. On the basis of hardware composed of different modules and fuzzy control algorithm, the system realizes the software design of vehicle automatic mechanical transmission system. The experimental results show that when the system is applied in practice, the gear selection time of the vehicle is between 0.2 s-0.3 s, and the gear shift time is between 0.3 s-0.4 s. The gap between the vehicle speed and the expected speed, and between the vehicle speed and the expected speed is small. The practical application effect is good.

Deep reinforcement learning for gearshift controllers in automatic transmissions

Control design for gearshifts in modern automotive automatic transmissions constitutes a challenging, time consuming task performed by highly trained experts. This is due to the fact that a variety of non-linear and partially observable systems need to be actuated, such that a comfortable shifting behavior is achieved within an sufficiently low shifting time. The presented approach leverages deep reinforcement learning (DRL) to control gear shifts, outperforming current state of the art controller performance. This requires formulating the shifting task as a Markov decision process by designing suitable action and observation spaces as well as a meaningful reward function. Due to the sample complexity of DRL methods, the control agents are trained in simulation and are subsequently transferred to a real transmission on a test bench. To successfully transfer DRL agents from simulation to reality, methods such as domain randomization and domain adaption leveraging evolutionary optimization are applied. To the best of the authors’ knowledge, this work is the first to successfully apply DRL for the closed loop control of a real world automotive automatic transmission of realistic complexity.

Efficiency Improvement of Transfer Drive Gear Bearings for an Automotive Automatic Transmission

Efficiency Improvement of Transfer Drive Gear Bearings for an Automotive Automatic Transmission

Dynamic Analysis of Helical Planetary Gear Sets under Combined Force and Moment Loading

The dynamic behavior of a single-stage planetary gear set with helical gears of multishaft automotive automatic transmissions has been studied, in which one component of the planetary gear set is imposed by additional external vertical and axial loading from countershaft gear pair in addition to the moment. Under these combined loading conditions, the contributions of the deflections of the ring gear and the carrier cannot be neglected. A three-dimensional nonlinear time-variant dynamic model considering not only the transverse, torsional, axial, and rotational motions of the gears but also the elasticity of the mounted shafts has been developed by combining the lumped parameter method with finite element method. The natural modes and the forced vibration responses due to static transmission errors have been obtained. The proposed dynamic model is employed to describe the effects of the combined external loading condition and positioning on the dynamic behavior of a four-planet system.

An assemblability check methodology for the kinematic configurations of automatic transmission planetary gear trains

Automotive automatic transmissions typically use a planetary gear train to transmit power at a number of desired output-to-input speed ratios. This is achieved by connecting the gear sets forming the train in various ways as well as connecting certain members to the input and outputs shafts as well as friction elements to hold them stationary. As the gear train is coaxial, the connections between the members of the gear sets as well as input, output and fixed member connections must be planar (i.e. do not intersect) for the transmission to be assemblable. This paper proposes a methodology to perform such planarity (assembly) checks to examine if kinematic configurations of a given concept design for an automatic planetary gear train be mechanically assembled by using a vertex addition algorithm based on graph theory. The proposed methodology is demonstrated through selected planar and non-planar transmission examples.

자동차 자동변속기 기어용 합금강의 열간 단조 성형에 따른 기계적 특성 변화에 관한 연구

This study investigated the effect of the changes in metal characteristics due to the hot forging on SCR420HB applied to ensure the optimal production of the hot-forging ratio on the mechanical properties of an automotive automatic transmission gear. The microstructural changes in the forging ratio were investigated by adjusting the forging range into multiple ranges from alloy steel. This was done in order to set the optimum forging range given the manufacturing process conditions during the hot forging of alloy steel parts with a carbon content of more than 0.8% wt. The effects of the content change in the microstructure on the mechanical properties due to the use of the part were examined.

Computing the power flow and mechanical efficiency of in-hub bicycle transmissions

Purpose – The analysis of power flow and mechanical efficiency constitutes an important phase in the design and analysis of gear mechanisms. The aim of this paper is to present a systematic procedure for the determination of power flow and mechanical efficiency of epicyclic-type transmission mechanisms. Design/methodology/approach – A novel epicyclic-type in-hub bicycle transmission, which is a split-power type transmission composed of two transmission units and one differential unit, and its clutching sequence table are introduced first. By using the concept of fundamental circuits, the procedure for calculating the angular speed of each link, the ideal torque and power flow of each link, the actual torque and power flow of each link determined by considering gear-mesh losses, and the mechanical efficiency of the transmission mechanism is proposed in a simple, straightforward manner. The mechanical efficiency analysis of epicyclic-type gear mechanisms is largely simplified to overcome tedious and complicated processes of traditionally methods. Findings – An analysis of the mechanical efficiency of a four-speed automotive automatic transmission completed by Hsu and Huang is used as an example to illustrate the utility and validity of the proposed procedure. The power flow and mechanical efficiency of the presented 16-speed in-hub bicycle transmission are computed, and the power recirculation inside the transmission mechanism at each speed is detected based on the power flow diagram. When power recirculation occurs, the mechanical efficiency of the gear mechanism at the related speed reduces. The mechanical efficiency of this in-hub bicycle transmission is more than 96 percent for each speed. Such an in-hub bicycle transmission possesses reasonable kinematics and high mechanical efficiency and is therefore suitable for further embodiment design and detail design. Originality/value – The proposed approach is suitable for the mechanical efficiency analysis of all kinds of complicated epicyclic-type transmissions with any number of degrees of freedom and facilitates a less-tedious process of determining mechanical efficiency. It is a useful tool for mechanical engineering designers to evaluate the efficiency performance of the gear mechanism before actually fabricating a prototype as well as measuring the numerical data. It also helps engineering designers to cautiously select feasible gear mechanisms to avoid those configurations with power recirculation in the preliminary design stage which may significantly reduce the time for developing novel in-hub bicycle transmissions.

Study of Stress Sources and Critical Stress Combinations for the Input Shaft of a Longitudinally Mounted Four Speed Automotive Automatic Transmission Model

In the present paper; two models of the input shaft for a Longitudinal Mounted four Speed Automotive Automatic Transmission for the first time were introduced to describe the input shaft critical loads. In the first model; the DC (Direct Clutch) connects two gears together. This gives no change in the set torque (the set output torque equal to the set input torque). In the second model; the ODB (Over Drive Brake) fixes one element of the planetary set. This is resulting, the gear set gives reduction ratio (the set output torque is not equal to the set input torque). So, the transmission input shaft is worked under two different working operating conditions of torque. Also, it is loaded by a two vertical loads which are coming from the turbine and planetary set loads respectively. They are shown that there are three critical combinations of forces (contact force, shear force, and normal force) applied on the input shaft. The critical forces can be possibility exist three types of cracks for the input shaft cross section they are: transverse (torsion stress), longitudinal (bending stress), and vertical (shear stress). The three cracks are studied in this article. The article considers three stress factors: shearing torsion stress, shear stress, and bending stress.

Fatigue strength of a paper-based friction material under shear–compressive loading

This paper deals with the fatigue strength of a paper-based friction material under the cyclic shear-compressive loading which is regarded as a real loading condition in an automotive automatic transmission. The paper-based friction material are composed of aramid fibers and phenolic resin. Static fracture and fatigue tests are carried out under various shear and compressive stress conditions. The S-N curves of the paper-based friction material under shear-compressive stresses are described by straight lines in a log-log diagram. The static fracture strength and fatigue strength are higher when the compressive stress is more dominant. The pure compressive cyclic deformation tests are also carried out to explain the fatigue strength of the paper-based friction material under compressive-dominant stress condition. From the tests, it is made clear that with increasing compressive stress, the friction materials becomes dense and the Young's modulus or slope of cyclic stress-strain relation becomes high, and as a result the strain range of the cyclic stress-strain relation remains as constant low value. Therefore, it is considered that the fatigue strength of the paper-based friction material is remarkably high under the compressive-dominant stress condition.

Connecting clutch elements to planetary gear trains for automotive automatic transmissions via coded sketches

This article presents a synthesis procedure to find feasible clutch layouts for a given planetary gear train clutching sequence. The method of constructing coded sketches for a planetary gear train is first introduced. In a coded sketch, all coaxial links, excluding the output link, are arranged in a specific order called a coaxial-link sequence. Based on the coaxial-link sequence, each link is encoded with three codes: x-code, y-code, and xy-code. Two identification rules are then concluded by examining these codes. Rule one tells how to arrange a band clutch without passage interference. Rule two is used to knock out the invalid clutching sequences leading to infeasible clutch layouts. According to the proposed coded sketches and rules, a synthesis procedure is then established for the purpose of finding all feasible coded layouts in a logical way from a given clutching sequence. Coded layouts can be directly and easily transferred to general clutch layouts. Two examples are used to demonstrate the feasibility of the synthesis procedure.

T0101-1-4 摩擦紙の引張および圧縮-せん断負荷下における疲労強度評価([T0101-1]マイクロ・ナノ材料システムの力学と強度・機能評価(1):ナノインプリント・シートの力学特性評価)

This paper deals with the fatigue strength the paper-based friction materials under cyclic shear-compressive loading which is regarded as a real loading condition in an automotive automatic transmission. The influence of ratios between the shear and compressive stress on the fatigue strength was examined. The fatigue strength decreases with increasing number of cycles. The static fracture strength and fatigue limit is high under the dominant compressive stress condition. The amount of deformation of the paper-based friction materials does not change with the compressive stress under the compressive loading, while the Young's moduli increase with increasing compressive stress.

Dynamic Modelling of Planetary Gears of Automatic Transmissions

In this paper, a generalized dynamic model for multi-stage planetary gear trains of automotive automatic transmissions is proposed. The planetary gear train is formed by N number of planetary gear sets of different types (single-planet, double-planet, or complex-compound), connected to each other in any given kinematic configuration. In addition, each planetary stage can have any number of parallel planet branches. A generalized power flow formulation and a gear mesh load distribution model are used to determine the stiffnesses, displacement excitations, and fundamental frequencies at the gear mesh interfaces. The natural modes are computed by solving the corresponding eigenvalue problem. The forced vibration response to gear mesh excitations is obtained by applying the modal summation technique. At the end, the model is applied to a three-stage planetary gear train representative of an automotive automatic transmission application to demonstrate the influence of coupling stiffnesses and the kinematic configurations on the natural modes and the dynamic response.

FEA-based prediction and experimental validation of clutch transient temperature in automatic transmission

Multiple-disk clutch packs are commonly used in automotive automatic transmissions to transfer power and to change gears. Owing to packaging-space restrictions and performance requests, many clutch packs have non-uniform loading characteristics, resulting in local stress and temperatures much higher than bulk targets. Extremely high local temperatures or temperature gradients in clutch packs can cause frictional material carbonisation, debonding, coning or many other failure modes. This paper describes the development of a Finite Element Analysis (FEA) model that is capable of predicting transient temperature in the multiple-disk clutch packs. The FEA predictions are correlated with experimental data. A good agreement, with 5% discrepancy in the clutch pack temperature rise during the first engagement is obtained. The developed method improves the understanding of the heat transfer characteristics during the clutch operating conditions, and reduces product development time and cost.

Phase unwrapping for large depth-of-field 3D laser holographic interferometry measurement of laterally discontinuous surfaces

A phase unwrapping method is developed to mathematically increase the depth-of-field for the 3D optical measurement of objects with laterally discontinuous surfaces, which contain disconnected high aspect ratio regions. This method is applied for laser holographic interferometry precision measurements. The phase wrap identification at boundary pixels, masking and recovery, dynamic segmentation and phase adjustment are developed to overcome the divergence problem in phase unwrapping of laterally discontinuous surfaces. An automotive automatic transmission valve body is applied as an example to demonstrate the developed method. Experimental results demonstrate that the proposed methods can efficiently unwrap the phase to increase the depth-of-field for laterally discontinuous surfaces. Effects of segment size and width of overlapped regions on the computational efficiency are investigated.

Simplified Kinematic Analysis of Bevel Epicyclic Gear Trains With Application to Power-Flow and Efficiency Analyses

A kinematic analysis technique is introduced to find the angular velocities of all links in bevel epicyclic gear trains. The method relies on previous work in graph theory. It improves on existing techniques used for analysis of planar geared mechanisms in its ability to accurately solve the kinematics of spatial geared mechanisms, particularly bevel gear trains, in a simpler manner. Usefulness of the method is demonstrated through its application to power-flow and efficiency analyses as well as its implementation in computer software. This discussion is limited to gear trains whose input and output axes are collinear, such as automotive automatic transmissions.

Epicyclic gear trains for automotive automatic transmissions

Epicyclic gear trains, which contain at least four coaxial links, are widely used in automatic transmissions. This paper presents a systematic methodology for the synthesis of epicyclic gear trains for automotive automatic transmissions. The graph representation of epicyclic gear trains is applied to develop an approach for the structural synthesis of the graphs of admissible epicyclic gear trains. Next, for each admissible graph the adjacency matrix of an epicyclic gear train is defined to develop an algorithm for the configuration synthesis of epicyclic gear trains. Using the proposed algorithm, all possible epicyclic gear trains for automotive automatic transmissions are systematically synthesized. In this paper, admissible epicyclic gear trains with up to ten links have been successfully synthesized. The results of work will lead to the creation of new multispeed automotive automatic transmissions.

Effect of Internal Gear Flexibility on the Quasi-Static Behavior of a Planetary Gear Set

Effect of flexibility of an internal gear on the quasi-static behavior of a planetary gear set is investigated. A state-of-the-art finite elements/semi-analytical nonlinear contact mechanics formulation is employed to model a typical automotive automatic transmission planetary unit. The model considers each gear as deformable bodies and meshes them to predict loads, stresses and deformations of the gears. Actual support and spline conditions are included in the model. The rim thickness of the internal gear is varied relative to the tooth height and gear deflections and bending stresses are quantified as a function of rim thickness. Influence of rim thickness on the load sharing amongst the planets is also investigated with and without floating sun gear condition. The results are discussed in detail and guidelines regarding the design of a planetary internal gear are presented.

A study of two-degree-of-freedom control of rotating speed in an automatic transmission, considering modeling errors of a hydraulic system

A proportional reducing valve is applied here to an automotive automatic transmission system to control shift operation. Its control system must be designed as a robust control system that considers modeling errors caused by changes in the characteristics of the valve. In this study, a braking mechanism of an automotive automatic transmission system is considered. Two-degree-of-freedom control of the rotating speed is studied, in which modeling errors due to changes in the characteristics of a proportional reducing valve are taken into account. A feedback controller is designed, based on μ synthesis, in which both changes in the characteristics of the valve and variations of a frictional coefficient are considered as uncertainties of a nominal model. Introducing a feedforward controller, a two-degree-of-freedom control system is constructed. The control system is examined through experiments using a commercial proportional reducing valve. The shift operation is precisely controlled by the control system under these fluctuating factors.

Improvement of fuel consumption for a vehicle with an automatic transmission using driven power control with a powertrain model

A total control system using a powertrain model is investigated for an automotive automatic transmission. The system provides e efficient control for both the engine and transmission which leads to better fuel consumption and acceleration feeling by optimizing shift timing and throttle valve opening. The new driven power control method using a total control system is described. A test vehicle equipped with an electronically controlled throttle valve is developed and the effectiveness of the proposed control method is verified.

Smooth Gear Shift Control System of Automatic Transmission Using Estimated Output Shaft Torque.

As for an automotive automatic transmission, a total control system using estimated output shat torque has been investigated in order to enhance drivability and improve fuel economy. The system provides efficient control for both engine and transmission, which leads to an enhancement of drivability by reducing shock during gear shifting. This paper describes a new smooth gear shift control method especially for 2-3 upshift using the total control system based on torque. A test vehicle equipped with an electronically controlled throttle valve has been developed and the effectiveness of the proposed control method has been verified.