Torque converter | EPFL Graph Search

A torque converter is a type of fluid coupling that transfers rotating power from a prime mover, like an internal combustion engine, to a rotating driven load. In a vehicle with an automatic transmission, the torque converter connects the power source to the load. It is usually located between the engine's flexplate and the transmission. The equivalent location in a manual transmission would be the mechanical clutch. The main characteristic of a torque converter is its ability to increase torque when the output rotational speed is so low, it allows the fluid, coming off the curved vanes of the turbine to be deflected off the stator while it is locked against its one-way clutch, thus providing the equivalent of a reduction gear. This is a feature beyond the simple fluid coupling, which can match rotational speed but does not multiply torque and thus reduces power. Hydraulic systems By far the most common form of torque converter in automobile transmissions is the hydrokin

Modélisation et réglage d'un entraînement à haute performance par un moteur réluctant

Michel Girardin

Usually, each phase of the direct reluctance motor is fed separately by its own inverter producing a squarewave phase current depending on the rotor position. In the present work, a star-connection of the three stator phases is used and the direct reluctance motor is fed by a three-phase switched inverter. The space phasor theory shows that three-phase sinewave currents can produce a constant electromagnetic torque. In this case, the rotating reference frame rotates at half of the rotor speed and in the opposite direction. This command strategy allows to reduce the stator deformation due to the electromagnetic radial force which is very high in this type of motor and which is mainly responsible for the acoustic noise. The electromagnetic torque control is realised by a sliding mode control of the three phase currents. In the rotating reference frame, it is possible to show that the eight commutation states of the switched inverter are placed around an ellipse in the complex plane of the derivatives of the space phasor of the phase current. A study of this ellipse has allowed to determine the maximal torque as a function of the speed for a given continuous voltage. It is important to insure that the torque reference will never exceed this limitation in order to avoid a pullout phenomenon, highly unwanted in the speed control. Despite the fact that the resolver inside the casing of the direct reluctance motor produces a small periodic error, it is accurate enough for the position measurement and to produce the three current references. However, the derivative of the position measurement provides a speed evaluation with such a ripple that the speed control cannot be outstanding. So, for the speed measurement, an additional laser rotary encoder is used. The experimental study in the steady-state mode of the speed control shows the presence of an electromagnetic torque ripple. This is a residual ripple caused by the dissimilarity between the stator poles teeth-shapes and the magnetic saturation effect. Although this torque ripple is rather low compared with the usual command strategy, two methods are proposed in order to compensate it. The first method is based on the use of a correction factor depending on the tooth angle. First, in steady-state conditions, the correction factor is stored off-line in a table. Then it is used in-line as a feedforward disturbance compensation. The second method of reducing the residual torque ripple consists in implementing an observer of variable disturbance. This is a disturbance observer able to determine the frequency content of the torque ripple. For instance, in order to observe the continuous component, the fundamental wave as well as the harmonics 2, 3, and 6, the observer must have ten poles. The main difficulty to deal with such an observer is the fact that each pole moves quickly as a function of the motor speed. So, in order to guarantee the observer stability over a large range of speed, the poles are located dynamically regarding to the motor speed by the way of a discontinuous adaptation of the feedforward coefficients. The theoretical study and the numerical simulation have allowed to formulate some criteria about the way of locating the poles. Experimental results confirm the efficiency of the observer of variable disturbance in order to reduce the electromagnetic torque ripple.

EPFL2000

Dynamics of torque control continuously variable transmissions

Robert Fuchs

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

Multi-level high-voltage power supply for dea application

Morgan Almanza, Yoan René Cyrille Civet, Lucas Depreux, Yves Perriard, Lucas Pniak

In order to reap the benefits of Dielectric Elastomer Actuator (DEA) high energy density, the electronics powering the actuator should be as small as possible. Knowing that only a small fraction of the energy delivered to DEAs is effectively converted into mechanical energy, the power supply has to be highly efficient and bidirectional in order to recover the unused energy, which requires more volume. Furthermore, DEA applications call for high voltage (up to 18kV for a 200um film), but as the voltage increases, so does the volume. In addition, there are no MOS transistors rated above 4.5kV, which limits our options. Since these goals are contradictory, we need to demonstrate the feasibility of DEA integration and find its limits. Therefore we present a prototype of Multi-Level Converter designed for DEA, which is a bidirectional structure that has proven to be especially effective in the power electronics field. A Multi-Level Converter overcomes the voltage limitation by equally distributing the desired voltage among levels; because the voltage of each level is sufficiently low, smaller available parts can now be used. Our prototype includes 20 levels of 1kV each. A numerical study of this topology has demonstrated that the efficiency is above 90%. Upcoming experimental works will discuss the advantages and the drawbacks of such Multi-Level Converters. Finally, the volume of the DEA will be compared with the volume of electronics.