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Electric cars
An electric engine is a machine that transforms electrical energy into mechanical energy through electromagnetic relations. Other electric engines are used in the opposite way, to change mechanical energy into electrical energy working as generators (PC in Control, 2008). Nowadays, EVs are not very common and, at least for the time being, too expensive to become an interesting alternative.
Gradually, we are seeing how car companies are adding EVs on their lines. These cars have many benefits including a complete reduction of urban air pollution and dependence on oil. On the other hand, adoption of EVs has a huge problem, the batteries.
To correct the problem of the low autonomy that the electric cars present, companies are developing more and more another type of cars: hybrid vehicles. Hybrid vehicles use two energy sources for their propulsion. One based on an electric engine and the other based on an ICE. (Juan Carlos Chicón Dominguez, 2006) Some of the advantages of hybrid electric vehicles come from the electric movement inception, like:
Regenerative braking, that allows to employ the energy generated in the braking to recharge the batteries.
Smaller ICE than in a fuel car. This lets reduce the vehicle weight as much as possible, decreasing the frictional losses.
A huge decrease of the fuel consumption. Around fifty percent of a normal consumption. .
Fewer emissions.
Change to alternative fuels, reducing the dependence of fossil fuels.
Configuration types for hybrid cars
There are 2 main configurations on hybrid cars, parallel configuration, shown in Figure 6, and serial configuration, shown in Figure 7. Some cars have a system that combines both configurations in a way that the engine can change its position in the schedule to work with the most favorable system.
The main feature of parallel configuration of hybrid cars is that the internal combustion engine has direct mechanic transmission with the wheels, as the electric engine. Both can work at the same time or alternate between them, working the ICE when the electrical engine has depleted the batteries or even when an extra power is needed. This configuration has the advantage to be able to supply more power to the car due to the fact that both engines can work together.
Serial configuration hybrid cars have also been named as Extended Range Electric Vehicles (EREVs). These cars also have two engines, but only the electric one is connected directly to the drive train, so the car is driven by electric traction. It has its ICE connected to a generator in order to recharge the battery pack when the car is being driven. A serial hybrid car has several advantages: it is less complex than a parallel configuration car, the engine can be placed anywhere because a mechanical transmission with the wheels is not necessary and the engine works very efficiently because it works inconstant rpm. Serial configuration hybrid cars contain:
An electric engine, i.e., the wheels are only moved by electric traction.
An ICE used as a generator to recharge the batteries.
A generator connected with the internal combustion engine to form a generator set.
Batteries to save the electrical energy.
Regenerative brakes. To save potential energy losses within the friction brakes and transform this energy to electrical energy that can be used for the electrical engine.
A plug in order to be attached to the electric power supply system to recharge the batteries. Normally, a fully electric car has around 90 km of autonomy; some examples are the Renault Twizy with 100 km of range (Renault Company, 2012) or the Reva, the bestseller electric automobile until 2009, with 80 km of range (Boxwell, 2011). There are some exceptions such as the Volvo electric car or Tesla Roadster. They can be driven about 400 km before recharging (Tesla Motors, 2012). A resume of the autonomies of different car types can be seen in Table 1.
Renault Fluence Z.E. (Technical specifications)
The car selected in this thesis to become an EREV is the Renault Fluence Z.E. showed in Figure 8, the electric version of the Renault Fluence. It is an EV with a pluggable battery. According to Renault website, its maximum speed is 135 km/h and it has a range of autonomy of 180 km according to the New European Drive Cycle (NEDC). The lithium ion battery is located behind the back seats. The weight of the system of batteries is 250 kg and it has an energy capacity of 22 kWh at 400 V. The car can be charged in a home plug by means of an adapter, but it is necessary to buy a specific adapter (Renault Company, 2010). The electric engine has a power of 70 kW (95 hp) and it weighs 160 kg.
Autonomy of the Renault Fluence Z.E
The medium autonomy of the electric engine of the Renault Fluence Z.E. is 180 km, and the battery capacity is 22 kWh. The autonomy is calculated with a method named “New European Drive Cycle” (Costas, Motorpasion, 2011). This method consists of a test in which a vehicle with between 3,000 and 15,000 km is placed in a room with a temperature between 20ºC and 30ºC, with the engine shut off for at least six hours. No air resistance or inclination of the road is considered in this test. The test is divided into two parts: urban and open road parts. The complete process is a route of 11 kilometers and 7 meters. Once all these conditions are accomplished, it is time to do the test:
Here are the steps of the test in urban zone:
1 The car is switched on and it remains 40 seconds motionless.
2 It is leaded to 15 km/h and then, it is stopped.
3 After waiting 50 seconds, it is leaded to 35 km/h and then, it is stopped.
4 After waiting another 50 seconds, it is leaded to 50 km/h, then decelerated to 27 km/h and stopped.
Solidworks and Solidworks Simulation
Solidworks is a mechanical design automation software that works in Microsoft Windows. This is an easy to learn tool that makes possible for mechanical designers to sketch quickly their ideas, to experiment with operations and dimensions and produce models and detailed drawings. ( Dassault Systems, 2012).
Solidworks Simulation is a design analysis system totally integrated in Solidworks. It proportions a screen solution for the next kinds of analysis: tension, frequency, buckling, thermal and optimization.
Solidworks simulation uses the Finite Element Method (FEM). FEM is accepted as the standard analysis method due to its generality and compatibility to be implemented in computers. FEM divides the model in numerous small simple pieces called “elements”, which replace efficiently a complex problem for a lot of simple problems to be solved simultaneously. The elements share common points determined as “nodes”, points at which different elements are jointed together; nodes are the locations where values of unknown (usually displacements) are to be approximated (Kriz, 2004). The model division process is known as meshing. The behavior of each element is well known under all the situations of possible supports and loads. FEM uses different shapes of elements.
An element response, at any time, is interpolated from the response of all the nodes of the element. Every node is described in detail for a certain number of parameters, depending on the type of analysis or element used. For the structural analysis, a node response is described, generally, for three translations. These are the degrees of freedom of the node.
Study of autonomy of Renault Fluence Z.E
To be able to choose a suitable fuel engine for the car of this problem, it is necessary to know the medium consumption of the car. The NEDC cycle does not provide useful information for this project due to the fact that this test is developed under standard conditions as explained in Chapter 1.6.5. For this problem with the Renault Fluence Z.E., an estimation is going to be made based in the test with the Renault Kangoo, Chapter 1.6.5. This estimation is of a consumption of 20kWh/100 km at 100km/h, which results in an average power need of 20 kW.
As the speed keeps decreasing, the consumption decreases too. For the calculations, the less favorable case is the one that is going to be studied. The results of the medium consumption obtained reflect a very high medium consumption value. This value may not be reached if an efficient driving is carried out or if the vehicle is not carrying on a lot of weight in the trunk or inside. Nevertheless, this is a good result for the calculations of the problem because the addition of a Range Extender supposes an extra consumption of electric energy, and furthermore, it is good to use the most unfavorable case in order to check if the minimum necessary autonomy if fulfilled. Once the estimation of the medium consumption is made, a fuel engine that supplies the needed power is searched.
Choosing the electric generator
In the case of this project, it is searched an engine, with as much power as possible in order to reduce the six hours of the normal electrical supply. For that, a study of the sales of electrical generators has to be done. Once the medium consumption of the electric car is known, a final comparison of the power of each engine can be carried out in order to choose the most powerful. A resume of the power of each engine can be seen in Table 2.
Choosing the place to put the engine
In this section, the process followed to select the position of the removable internal combustion engine will be explained. All the possible options will be taken into account; those that are not feasible will be deleted and all that could be interesting to be studied or designed will be selected by means of a classification tree. This method is explained in Chapter 1.6.10. In order to simplify the problem, the options will be divided into two fields, inside and outside the chassis. Below, all the options of each possibility will be discussed, taking into account the advantages and disadvantages and impossible options will be discarded. First of all, some guidelines about the chassis will be explained.
The chassis is the part of a vehicle that supports the entire load and protects it from impacts. Depending on the shape, it can be classified into different types. The car chosen for this thesis is the Renault Fluence Z.E., whose features can be found in Chapter 1.6.4. It is a three-box configuration with separate compartments for the engine, the passengers and the cargo as described in Figure 24. On Figure 23 there are all the possible positions for the ICE.
Table of contents :
1 INTRODUCTION
1.1 Background
1.2 Problem
1.3 Goal
1.4 Purpose
1.5 Method
1.6 Literature review
1.6.1 History
1.6.2 Electric cars
1.6.3 Configuration types for hybrid cars
1.6.4 Renault Fluence Z.E. (Technical specifications)
1.6.5 Autonomy of the Renault Fluence Z.E
1.6.6 Ways of charging
1.6.7 Connection with the batteries
1.6.8 Models of electric generators
1.6.9 Attaching systems
1.6.10 Classification tree
1.6.11 Brainstorming
1.6.12 Hitch hook types
1.6.13 Solidworks and Solidworks Simulation
1.6.14 Welding
1.7 Limitations
2 IMPLEMENTATION
2.1 Study of autonomy of Renault Fluence Z.E
2.2 Choosing the electric generator
2.3 Choosing the place to put the engine
2.3.1 Analysis of the positions
2.4 Hitch hook analysis
2.4.1 Design of the attaching system
2.5 Design of the structure
2.5.1 Choice of the shape of the structure
2.5.2 Profile of the bars
2.5.3 Dimensioning the force
2.5.4 Solving the problem in Solidworks
2.5.5 Estimation of the attaching system
2.5.6 Calculation of the welding
2.6 Exterior design
2.6.1 Cover case
2.6.2 Signaling of the system
2.6.3 Security chain
2.6.4 Final appearance of the exterior design
3 RESULTS
4 ANALYSIS
5 CONCLUSIONS
6 FUTHER WORK
7 APPENDIX
7.1 Appendix 1
7.2 Appendix 2
7.3 Appendix 3
7.4 Appendix 4
7.5 Appendix 5
7.6 Appendix 6
7.7 Appendix 7
7.8 Appendix 8
7.9 Appendix 9
8 REFERENCES
