Avaliação Geométrica de um Volante de Inércia Para um Sistema KERS (Kinetic Energy Recovery System)

COB-2019-0598

 ANALYSIS AND OPTIMIZATION OF A FLYWHEEL FOR APPLICATION IN A MECHANICAL KINETIC ENERGY RECOVERY SYSTEM (MKERS)  ON AN ONROAD MOTORCYCLE

Joyce Ingrid Venceslau de Souto

Departamento de Engenharia Mecânica, Universidade Federal de Campina Grande, Campina Grande/PB, Brazil

[e-mail]

Abstract. A flywheel is a machine element used for a long time constituting one of the first existing ways of storing kinetic energy. The present paper is intended to create circumstances that provide improvement of performance and cost of this study object starting from an initial model whose development is focused on a Mechanical Kinetic Energy Recovery System (MKERS) with application on an onroad motorcycle. Thus the optimization process was made possible by further study of existing theory about the proposed theme, use of CAD software -  Autodesk Inventor - to assist in geometry modeling and also in the finite element analysis that made possible the stress analysis and determination of safety factor. This whole process constitutes itself as optimization because it was not take into account in the development of the initial model and the obtained results are intended to help build this component and to support development of the other MKERS components in the future.

Keywords: flywheel; energy; recovery; MKERS.

1. INTRODUCTION

A flywheel is basically a piece in cast cylindrical format that is capable of storing energy through restoration of angular momentum. It is known that during braking there is a noticeable percentage energy present in the wheels which is transformed into thermal and sound energy. The function of an inertia flywheel in this kind of application is to store this energy that would be lost and restore it back to the engine producing momentary torque. Its applications extend from the potter’s wheel and spinning wheel which are objects used since ancient to the flywheel modules that constitute the KERS used in Formula 1, being one of the simplest and most current mechanical forms of to store energy and increase power to the engine. Currently this form of storage acquires notoriety in scientific research for not having as much impact to the environment compared to batteries for example, be cheaper and have great potential for efficiency and reduce fuel consumption. The most sophisticated models are manufactured from composite materials with complex specifications (especially high energy density) and the system has also magnetic bearings capable of reduce energy losses from the flywheel high-speed operation among other elements that enhance the efficiency of the flywheel.  

The moment of inertia of a flywheel, as well as the energy stored in it, is proportional to its mass and the square of the internal and external radius of the circular face of the cylinder. Thus, the optimization process involves increasing the size of the external radius that increases the amount of stored kinetic energy, but at the same time decreases the thickness and modify geometry so that the flywheel model has a higher energy density, in other words, it will be capable of storing more energy per unit mass. The effects of this are the best use of space theoretically dedicated to the flywheel and lower cost in relation to the material, at the same time as this allows the increase in the amount of energy stored in the flywheel. Specifically, all parameters related will be calculated, based on pre-established or tabulated values according to a particular application. Once this is done, then it will be possible to refine the flywheel design on Autodesk Inventor, as well as the static analysis through the Finite Element Analysis (FEA) to ensure the calculations made a priori, and compare the mass/stored energy of the evaluated models in relation to the generic model initially used, being possible to choose the most efficient of them.

 

1. THEORETICAL BACKGROUND

 

1. Alternatives and advantages

It is primordial to emphasize the importance of the flywheel as an alternative energy source because the new trend of project development is to give priority to the ecologically correct, especially in the mobility field and this requirement the flywheels are able to meet if compared to other energy storage alternatives. Beyond that, this alternative has many advantages that were taken into account for the MKERS development.

In some theses (Michael Mathew, 2008) and scientific articles (Radhika Kapoor e Parveen, 2013), their authors are concerned to explain the advantages for the application of flywheels over other alternatives such as chemical batteries and, more generally, of the advantages that MKERS has over other forms of energy storage. From this it can be perceived that the flywheels can offer a maximum level of energy in a stable way and several stages of power, depending on the configuration of its transmission. Besides, in case of flywheels, it is not necessary to study the state of discharge due to the minimal influence that this phenomenon has on the principle of operation. Also it is notorious that it is responsible for a reduction of fuel consumption whose efficiency in this requirement is comparable to that of supercapacitors when applied to systems that have internal combustion engines or hybrids, knowing that one of its functions is also to minimize the variation of the rotation and energy oscillations of the system in which it is inserted and this oscillation control is one of the most important factors when it comes to fuel consumption.

Besides everything already mentioned it is observed that of all the energy storage mechanisms the flywheel is one of the cheapest, losing it only to batteries. This can be explained by the commonly selected materials that are easily found on the market and the manufacturing modes are usually simple so there is no noticeable cost in this regard. Also it can be emphasized that, unlike batteries, the storage capacity of a flywheel does not decrease with its life time and in addition, it can have high energy density depending mainly on the selection of material which allows a more compact and lightweight design, making it the perfect choice for energy storage in applications that have limited space such as motorcycles.

 

1. Applications

At the present juncture there is a very wide range application area and complexity regarding to flywheels. In recent work (Hedlund et al., 2015) it was carried out a detailed review of numerous automotive applications of systems using inertia flywheels in order to recover energy. It can be highlighted its use in: mobility (buses, garbage trucks, cars, motorcycles and bicycles), container cranes, construction machinery, train stations, frequency regulators, among others. Due to circumstances of the present study it will be better explained some applications of inertia flywheels for the mechanical energy recovery system and, specifically, for motorcycles.