Shell eco Marathon is a competition in which student from all study background is invited to build up a car that able to complete the longest distance in track in minimum fuel consumption. The competition was categorized that defines the system and types of running engine. There are two major categories that is prototype car and urban car concept. Prototype car is a car concept where it must be running in three tires, with a very basic mechanism yet ergonomic to the driver. While in urban car concept, the car is build in four running tire or in other words it similar to the real car system. In this competition, the car invented have to complete the task by travelling the circuit ( Sepang International circuit Kuala Lumpur ) within 20 minutes.
Shell eco Marathon competition does not consider the time to finished the travel but contestant are required to complete the travel with minimum given fuel. This means a lot to the efficiency of the car. The minimum allowed speed is about 30 km/h which approximately equal to 8.3 m/s.
Sem Mechapro team representing Universiti Malaysia Pahang to take part in prototype category. During last participation, the team manage to complete the competition with the others teams from Malaysia with overall achievement ranked at the third place. The best completed distance travelled is 101 km which the best result recorded in MPG as much as 238.
Considering the type of the competition, we care about the total weight of the car. The main part that will contribute to the increment of the weight is the chassis of the car. Thus in this analysis we will focus on the weight of the driver. The chassis configuration must be light enough but developed at high total stiffness or rigidity to avoid deformation that might occur during accidental collision. For safety reason, first we will consider on deflection of the chassis component especially at the concentrated load exerted by the driver. However, considering “if situation”, then we will look at the accidental collision. The roll bar is very important to protect the driver if the car get upside down. In order to develop the car chassis that have high resist to deformation upon load, first we have to study the profile of the chassis that needed to fabricate. For this coming competition, the team has decided to build the ‘space frame chassis” rather than other type of chassis design.
Space frame chassis design is a tubular space frame that employs dozen of circular section tubes which provides the maximum strength and it is positioned in different direction to provide mechanical strength against the force from anywhere. Space frame chassis uses a series of straight tubes and welded together to achieve strength and rigidity with minimal weight. A space frame consist of metal element such as steel or aluminum tubular pipes placed in triangulated format to support the loads from vehicle caused by suspension, engine, driver and aerodynamics effect ( Cristopher,2004). Space frame chassis is chosen considering the low cost of fabrication compared to other type of chassis fabrication such as monocoque. However, before we go to fabrication, we need to understand the principle of how this welded tubular component is working together so that the part will perform at the best result. By performing the simulation in FEMPRO, it is important to know where to draft the connector.
Fundamental principle of a chassis design is that the chassis is designed to achieve rigidity in term of torsional or lateral forces. The concept of supporting frame is by sticking a diagonal element to a rectangular frame to avoid extension of the frame when applying the load. For this competition, we define the main component as the front box, driver compartment and engine compartment.
There is several parameter that are important to take into account. Although the car will run at low speed, the aerodynamic effect contributes to lateral forces coming from the front. The frame has to overcome the load from front, side, rear and from the top ( in case of the car get upside down during accidental collision). The space frame is by nature is are very efficient. Bending moment are transmitted as tension and the pressure load along the length of each tube. Manufacturing of the frame can be done by welding extruded tubes together using conventional method.
