Solar Electric Road Vehicle

Progress Report

Of

Mechanical System

Project SERVe:”Solar Electric Road Vehicle”

October 2014

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Submitted by

Team SolarMobil Manipal

         DEPT. OF AERONAUTICAL AND AUTOMOBILE ENGINEERING[pic 2][pic 3]

        MANIPAL INSTITUTE OF TECHNOLOGY

         (A constituent institution of Manipal University)

Progress Report On

Structures Subsystem

Amol Grover, IIIrd Year, Mechanical Engineering, MIT

INTRODUCTION TO STRUCTURES SUBSYSTEM

The chassis, for all intents and purposes, is the skeletal system of the car. It is the load bearing member of a car, responsible for withstanding the static as well as dynamic loads acting on the car during the course of its operation.  In addition to this, it must also double as a safety feature in case of impact and accidents. The chassis needs to be designed so as to increase performance of the entire car and better the handling without compromising on the human comfort and safety. Thus, the automotive chassis has three main goals:

1.  Hold the weight of the components of the car.

2. Withstand the dynamic forces acting on the car such as acceleration and deceleration loads, gradient loads, cornering loads among others.

3. Rigidly hold the suspension components while the vehicle is in motion and dissipate the loads transferred from the same. These loads include bump forces, torsional forces and roll over forces.

4. Provide a framework for the safety of the driver. The chassis must be able to withstand impact loads from the front, side and rear directions.

5. Provide a comfortable experience for the driver and the passengers. The chassis must not interfere with the actions of the occupants. The chassis must also have suitable flexural rigidity.

6. Meet the requirements as postulated in the applicable rule book.

SPACEFRAME CHASSIS

A space frame is a truss like, light weight rigid structure constructed by interlocking struts in a geometric pattern. This structure derives its strength from the inherent strength of the triangular structure.

Its greatest advantage is that it transmits flexing loads or bending loads as tension and compression along the length of each strut. This allows this design to withstand higher loads, since nearly all materials have greater strength in withstanding axial forces as compared to shear forces. The top and bottom chords of a space frame carry the tension and compression loads. While the webs carry shear loads as a whole, individually they are still subjected to axial loads, the exact nature of which depends on loads and nature of deflection. Another advantage is that the webs also stabilize each other, preventing buckling.

Another important thing of note is that in a space frame, the nodes are treated as revolute joints, which means that they have a single degree of freedom. A drawback of this kind of chassis is that it encloses large amounts of working volume which makes access for the driver difficult. This can be solved by adding removable frames. The lack of bending stresses in the structure allows the joints to be modelled as pin joint and therefore, does not affect the efficiency of the chassis.

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ERGONOMICS OF CAR

It is important to note that vehicle packaging is meant to provide suitable space for people and parts in vehicle; human factor consideration is a must for the integration of the total design. If the vehicle controls are not strategically placed, the user will have difficulty in operating the vehicle and the vehicle will not be capable of reaching its peak performance. One should also make sure that the interior equipment doesn't distract driver's eye attention while driving and are put in places that will not damage anybody in case of accident.

The cockpit was designed such so as to accommodate a range of drivers within the stipulated rules and regulations. The important dimensions in the ergonomic apparatus are the seat rest angle, seat base angle, steering location and the position of the hip point. The ergonomic apparatus was designed and built with each of the above dimension adjustable. Compilation of data was then done to observe and obtain the optimum angles and position of seat

GENERAL SPECIFICATIONS OF THE CAR:

Progress Report On

Vehicle Dynamics

Kunwardeep Khanna, IIIrd Year, Mechanical Engineering, MIT

INTRODUCTION TO OUR SUSPENSION SYSTEM:

The prominent goal of a suspension system is set by its need, the type of car being made. We are building a passenger solar car, so, the comfort of the passengers is of prime importance and since, we are also racing the car, little fine tuning to performance would be perfect. The suspension setup must also ensure that the car is always in contact with the road for good handling and safety of the driver and passengers. ‘Wingeo’ software was used in designing the suspension geometry. A total of more than 60 or 70 iterations have to be made to achieve the desired geometry. The use of push rod type suspension is made, this eliminates the higher inclination and thus the lower efficiency of the spring. Also, the bell crank allows for various motion ratios thus various wheel rates can be achieved from one spring itself.

The car would have an unequal, non-parallel double wishbone suspension setup. This was chosen for various reason, they are:

1. The camber rate is versatile. If we want to save the tire for making the car commercial or a subtle camber rate during the corners giving good grip of the road both can be done by simple change in hard points.
2. The designing and manufacturing a double wishbone suspension is easy and economical.

The roll and ride rate calculations were made keeping in mind the purpose, a comfy suspension system which could help the car to stick to the road all the time. So, we designed a soft suspension setup. Keeping this in mind, the ride frequencies were decided and the wheel rates were calculated and complainant roll gradient was achieved, with the elimination of ARBs. The rear suspension system is designed to complement the front through the roll axis inclination, which decides the transient stability of the car. The side view geometry has been analysed and ‘anti’ features were decided to reduce the pitching of the car at the same time keeping the suspension soft, giving the car a less pitch geometry.