Automatic transmission

Résumé

An automatic transmission (sometimes abbreviated AT) is a multi-speed transmission used in motor vehicles that does not require any input from the driver to change forward gears under normal driving conditions. The most common type of automatic transmission is the hydraulic automatic, which uses a planetary gearset, hydraulic controls, and a torque converter. Other types of automatic transmissions include continuously variable transmissions (CVT), automated manual transmissions (AMT), and dual-clutch transmissions (DCT). The 1904 Sturtevant "horseless carriage gearbox" is often considered to be the first true automatic transmission. The first mass-produced automatic transmission is the General Motors Hydramatic four-speed hydraulic automatic, which was introduced in 1939. Prevalence Globally, 43% of new cars produced in 2015 were manual transmissions, falling to 37% by 2020. Automatic transmissions have long been prevalent in the United States, but

Source officielle

https://en.wikipedia.org/wiki/Automatic_transmission

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Concepts associés (16)

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Cours associés (19)

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Séances de cours associées (24)

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With the increasing concerns in the impact of automotive emissions of CO2 and NOx on the environment combined with today's speculation on oil crude supply, the need to find solutions reducing the fuel consumption and emission of tomorrow's cars is more than ever present. Although the first continuously variable transmissions (CVT) appeared over a hundred years ago, it is only with the recent technological improvements in material durability, lubrication oil as well as control related hardware and software, that these transmissions have proved their capabilities. Because of their ability to decouple the engine from the wheel speed, CVTs enable significant fuel gains by shifting the engine operating point for a certain power demand toward higher torque and lower speed. A CVT can be regarded as a system dedicated to converting the torque delivered by the engine to the wheels. Conversely, for the engine speed control, it can be seen as an actuator applying a load to the engine. Two control concepts of CVTs are recognized. First is the concept of ratio control, which is a natural extension to fixed gear ratio transmissions, enabling an actuation of the transmission ratio. Second and less conventional, is the torque control concept, which sets the torque to be transmitted. It is the particular mechanism of these variators that allows the transmission to automatically shift to the appropriate ratio. Torque control CVTs extend the benefits obtained with conventional ratio control CVTs as they provide a direct control of the load applied on the engine, resulting in a straightforward control of the powertrain. Moreover, when such CVTs are combined with an epicyclic gear train in a split torque arrangement to form an infinitely variable transmission (IVT), virtually no control is required for the operation at the geared neutral point (infinite or zero speed ratio depending on the definition). However, the extended ability of torque control CVTs to decouple the engine and the vehicle speeds causes strong internal interactions, which must be fully understood for their development. The objective of this thesis is to provide a comprehensive and coherent set of analytical tools for the development and operation of torque control CVT powertrains. The classical method of modeling, performance analysis and control is applied to the Torotrak IVT Series 3 and its torque control full toroidal variator. Each of these steps gives a different perspective of the dynamics involved within the variator, of the interactions of the variator with the surrounding subsystems (hydraulics and driveline) and of the powertrain control. The contribution of this work is threefold. Firstly, the most relevant dynamics involved in TC/CVT-based powertrains are described with an application to the Torotrak torque control IVT. The main technical achievements are the development and validation of a model for simulation of the full toroidal variator, an open-loop performance analysis of the powertrain and the development of a control strategy for the engine operating point based on the nonlinear input-output feedback linearization technique. Secondly, this work broadens the general theoretical knowledge base of the operation of CVT powertrains. The two control concepts are compared and formally defined resulting in a new and original classification of transmissions. Also, the problem of powertrain control is formalized with the development of high-level, low bandwidth models of the engine, the transmission and the vehicle featuring properties similar to those of the ratio control CVT powertrain model. Thirdly, the formal and progressive analysis made throughout this work shows how the classical method of modeling, performance analysis and control can be applied to complex systems. This relies most of all on the development of models of varying complexity adapted to the requirements of the system analysis, design and control.

EPFL2006

Chargement

Coupling non-conforming discretizations of PDEs by spectral approximation of the Lagrange multiplier space

Simone Deparis, Antonio Iubatti, Luca Pegolotti

This work focuses on the development of a non-conforming method for the coupling of PDEs based on weakly imposed transmission conditions: the continuity of the global solution is enforced by a finite number of Lagrange multipliers defined over the interfaces of adjacent subdomains. The method falls into the class of primal hybrid methods, which include also the well-known mortar method. Differently from the mortar method, we discretize the space of basis functions on the interface by spectral approximation independently of the discretization of the two adjacent domains. In particular, our approach can be regarded as a specialization of the three-field method in which the spaces used to enforce the continuity of the solution and its conormal derivative across the interface are taken equal. One of the possible choices to approximate the interface variational space – which we consider here – is by Fourier basis functions. As we show in the numerical simulations, the method is well-suited for the coupling of problems defined on globally non-conforming meshes or discretized with basis functions of different polynomial degree in each subdomain. We also investigate the possibility of coupling solutions obtained with incompatible numerical methods, namely the finite element method and isogeometric analysis.

2019

Chargement

Active origami platforms for human-robot interactions

Frédéric Henri Vaskin Giraud

Robots are employed to assist humans in lengthy, challenging, and repetitive tasks. However, the fields of rehabilitation, haptics, and assistive robotics have shown a significant need to support and interact with people in their everyday life. To facilitate these further needs, robots must overcome constraints in compactness, degrees of freedom (DoF), and mechanical performance. However, developing a robot with these characteristics is challenging for conventional mechanics. First, creating a meso-scale device requires the assembly of small components, which is laborious and increases manufacturing cost, time, and complexity. In addition, devices with several DoF and functionalities also require more parts to create numerous links and joints, actuators, and thus space, affecting the compactness of systems. Finally, aiming for mechanical performance in terms of force, speed, and motion range requires transmissions or bulky actuators, which also influence the size of the system. This thesis attempts to overcome the limitations of conventional mechanics by using origami robots, an alternative design approach for creating meso-scale structures with numerous folding joints. It consists in stacking layers of functional material to achieve low-profile and scalable structures that fold into 3D. Using this method, we developed three hybrid robots combining the decades of experience of conventional mechanics with the advantages of origami robotics. First, to enhance the performances of robots at the meso-scale, the creation of compact low-profile compliant transmissions benefiting from origami's minimal assembly of functional layers was explored. The transmissions obtained can reproduce conventional kinematics or generate unconventional motions using materials properties. Second, the development of multi-DoF compact robots was studied using the aforementioned low-profile compliant transmissions to create a multi-functional structure. The resulting robot is a fingertip haptic device called Haptigami that can render vibrotactile and three-DoF force feedback without compromising bulkiness. Then, this study aimed at creating a meso-scale, multi-DoF, and mechanically efficient robot. We combined the previous device contributions and developed Flexure Variable Stiffness Actuators (F-VSA), a novel compliant actuator that uses the origami flexure hinges' inherent stiffness to avoid hindering mechanical simplicity. Finally, we developed a software architecture that enables high-level control of the human-robot hardware and is compatible with multiple simulation engines. We used this architecture to control our robots and provide feedback to the user, based on interactions in a virtual environment. These novel robots rely on non-conventional structures, actuators, and kinematics that require exploring and testing suitable control strategies. Hence, kinematic and stiffness models were developed and used to tune the position, force, and stiffness of the end-effector. Several characterization platforms and experimental protocols suitable for testing our unique robotic systems were also developed to assess their precision and efficiency. Consequently, the results of this study pave the way for the development of robots that adapt to multiple environments, interactions, and application scenarios, compatible with the human bandwidth without hindering the user's motion and comfort in everyday life.

EPFL2022

Chargement

EPFL2006

Active origami platforms for human-robot interactions

Frédéric Henri Vaskin Giraud

EPFL2022