Chassis Design of Self- Propelled Onion Harvester

Abstract

SAE TIFAN is an intercollegiate competition organized by Society of Automotive Engineers (SAE) to design, build and Agriculture harvesting vehicles. Chassis is an important part of the vehicle that supports the body and other different parts of the vehicle. It also surrounds and protects the occupant in case of impact and roll over incidents and also gives the aesthetics of the vehicle. The paper deals with selection of material and cross section for the chassis and analysing the frame design for different loading conditions to predict whether it will survive various impact scenarios using ANSYS workbench. The chassis design will be based on SAE TIFAN India 2021 rule book taking safety and other aspects into account. The results from these simulations indicate that the frame is safe enough for the variety of worst-case scenarios tested.

Introduction

I. INTRODUCTION

The SAE TIFAN is an event for the undergraduate students of engineering, organized by the Society of Automotive Engineers. It serves as a platform for young engineering students to showcase their skills by designing, fabricating and validating a single seater onion harvester and acquiring real-life experience while overcoming obstacles and challenges. The main function of a chassis is to support the vehicle's mechanical components and deal with static and dynamic loads, without deflection or distortion. It should be designed in an ergonomic and strong effective manner at optimum cost and weight for agricultural purposes. In the current scenario available are over designed i.e., their structural rigidity and sturdiness are more than requirement. This leads to an increase in weight and cost of manufacturing. Dnyaneshwar Mule’s analysis allowed the addition of three important and key structural components to help the vehicle withstand front and side impacts as well as the forces due to the loading of the shock mounts. Om Patil analysed four interactions of the frame design. A simple loading case was applied to the different frame versions, and the frame design with the highest factor of safety was chosen for Torsional bending, Vertical bending. Yash Chikhalkar thoroughly dealt with various load analysis on chassis and considerable Factor of Safety (FOS) applied to the roll cage design to minimize the risk of failure and possible resulting injury. This clearly reaffirms the vehicle's ability to withstand extreme conditions. While Nishant Rahangdale and other team members discuss the finite element analysis of chassis in detail using ANSYS software. The paper deals with one such design model of SAE TIFAN chassis as per the guidelines of SAE TIFAN India 2021. The work discussed in the following sections include the Material selection, Cross-section selection, Design of a Chassis and Analysis of the Chassis.

II. DEFINITION

The chassis of an automobile is defined as a frame supported on springs and attached to the axle that holds the body and engine of the vehicle. Chassis is a French word and was initially used to denote the frame parts or basic structure of an automobile. It is the backbone of the vehicle.

It is the main mounting for all the components. So, it is also called a Carrying unit. The chassis of an automobile consists of following components suitably mounted:

1. Engine
2. Transmission system
3. Suspension system
4. Wheel Assembly
5. Steering System
6. Brakes System
7. Fuel Tank
8. Other Miscellaneous Components

All the components listed above are mounted in either of the two ways, viz., the conventional construction, in which a separate frame is used and the frameless or unitary construction in which no separate frame is employed. Out of these, the conventional type of construction is being used presently only for the heavy vehicles. While for the vehicle the same has been replaced by the frameless type or the monocoque chassis.

The purpose is to design and manufacture tubular space frame chassis that should be strong enough to absorb the energy when front, back, side, torsional loads are applied. For the purpose of the application on a high-performance vehicle, it has to meet the following criteria:

a. Minimize the weight to stiffness ratio

b. Maintain Low Center of Gravity

c. Reasonable material and manufacturing costs

d. Create a solid base chassis to evolve on for years to come

e. Aesthetically pleasing design Chassis

A. The Chassis

The chassis is possibly the most important part of any vehicle. Its main role is to provide the vehicle with a main structure which all other components can be fixed to. The chassis must be rigid in both torsion and bending. The chassis must be able to accommodate and support all the components of the vehicle and any occupants and must absorb all loads without excessive deflection.

B. Types of Chassis Design

1. Ladder Frame Chassis

The ladder frame chassis was the earliest type of chassis used. It was widely used for the earliest cars until the early 60s. The design is, as the name suggests, similar to a ladder. There are two longitudinal rails running the length of the vehicle which are connected together by several lateral and cross braces.

2. Tubular Frame Chassis

The tubular frame was the next logical step up from the ladder frame. A tubular frame has a number of features that distinguish it from a ladder frame and add massive advantages. A perfectly designed space frame would have the tubular sections arranged so that the only forces on them are either tension or compression.

3. Monocoque Chassis

The Monocoque style of chassis is used by almost all car manufacturers today. A Monocoque is a one-piece structure that defines the overall shape of the vehicle. This type of chassis is very attractive to mass production as the process can be automated very easily. The structure also has very good crash protection as crumple zones can be built into the structure itself.

4. Backbone Chassis

A backbone chassis is a simple style of frame that uses a central backbone running the length of the chassis that connects to the front and rear suspension attachment areas. The backbone usually has a rectangular cross section. The body of the vehicle is then placed onto the structure. This type of chassis is used sometimes for small sports cars however it provides little or no protection against a side impact and so requires the body to be designed to accommodate this.

III. DESIGN CONSIDERATION

The layout manner of the chassis includes many steps, from the preliminary project to the mission of chassis layout to the beginning of production. These steps are; to become aware of the restriction, decide the specified overall performance standards, study layout techniques and technique, use of CATIA software program to layout chassis and ultimately begin creation. Throughout those steps, picks should be made based on the objectives which might be to be executed to meet the performance requirement.

The designer of the chassis needs to have an idea as to how all additives of the vehicle are going to feature when it comes to every different.

As a result, the designer has to understand how all parts ought to interact and take this interplay into account while designing the body. The design of a vehicle chassis for that to be counted, is going to be primarily based on suspension points, powertrain format, driving force function controls, protection, and many others. These vital points must come collectively to form a powerful bundle for the car to perform as meant.

A. Various Loads Acting on Chassis

1. Weight of the vehicle and passengers, which causes vertical bending of the side members.
2. Vertical loads when the vehicle comes across a bump, which results in longitudinal torsion due to the wheel being lifted (or lowered) with other wheels at the usual road level.
3. Loads due to road camber, side wind, cornering force while taking a turn, which result in lateral bending of side members.
4. Load due to wheel impact with the road obstacles may cause that particular wheel to remain obstructed while the other wheel tends to move forward, distorting the frame to parallelogram shape.
5. Engine torque and braking torque tend to bend the side members in the vertical plane.
6. Sudden impact loads during collision, which may result in a general collapse.

B. There are several factors that must be considered when designing the frame

1. Safety

Fortunately, the SAE TIFAN rules committee has set up a group of rules requiring certain tubing sizes in areas of the frame critical to driver safety in the event of an accident. These rules define outer diameters and wall thicknesses for the front bulkhead, front roll hoop, main roll hoop, side impact tubing, roll hoop bracing, and front impact zones. The stated rules are adhered to without deviation so that the driver may be safe and the car can pass technical inspection at competition.

2. Stiffness

Normally, a vehicle chassis should be as stiff as possible to withstand torsion. This is to facilitate easier suspension tuning. When determining the handling qualities of a vehicle, one of the most effective methods of adjusting the amount of oversteer and under-steer is the adjustment of roll stiffness, front-to-rear.

3. Torsional Stiffness

Torsional order to design a car of maximum torsional stiffness the basis or generalized equation for torsion must be examined. Stiffness is the resistance of the frame to torsional loads.

T = GθJ/ L

The above equation is a simple formula that relates the angle of twist to the applied torque, with J representing the shafts polar moment of inertia, with θ denoting the resultant twist of the shaft, G representing the shear modulus of the material and L being the length of the shaft.

Now a chassis can be made extremely stiff by adding significant amounts of material to the frame. However, this additional material might degrade the performance of the car because of the added mass. Therefore, while designing a race car chassis it is important to get a balance between the weight and stiffness of the chassis.

4. Weight

As discussed earlier, wherever possible, weight should be minimized. Just as important as weight, is mass moment of inertia. A vehicle with a lower mass moment of inertia will be able to turn more quickly. In order to reduce mass moment of inertia, all weight on the chassis is pushed as far as possible towards the center of the vehicle.

5. Ergonomics

Ergonomics, or the study of human-machine interfacing, is important to vehicle design because the ultimate control of the vehicle belongs to the driver. When designing this ‘interface’ between person and machine, several aspects should be taken into account so that the best system of control is produced.

6. Seating Position/Field of View

A key input to the interface is the driver’s vision. The field of view should include visibility ahead and to the sides of the vehicle (Approximately 180-degree arc– more is even better) and visibility of the road surface. The driver needs a sufficient level of information about the nature of the oncoming road surface and what is occurring beside them through peripheral vision to drive confidently. If the driver must strain their neck to see enough to feel confident.

7. Control Positions

Vehicle controls should be within a comfortable reach of the driver and be comfortable to operate. Controls that are awkward to reach or difficult to operate will distract the driver and potentially result in more driving mistakes.

IV. STRUCTURAL DESIGN

Mass

Estimated Load of the Vehicle The various loads which are acting on the vehicle are estimated according to the centre of gravity of the vehicle. As the various loads acting on the vehicle are distributed are shown in the below table.

By considering miscellaneous masses such as the wheels, fuel tank etc. The weight of the car is considered to be approximately 410 Kg.

Table 1: Mass Distribution of Harvester

V. MATERIAL SELECTION

Material selection for SAE TIFAN vehicles is one of the key design decisions that has great influence on the safety, reliability and performance of the vehicle. It also decides the weight of the vehicle, fabrication processes and cost. The qualities that were given due importance are yield strength, the strength to weight ratio and good weldability property. As per the guidelines of the SAE TIFAN rule book the minimum carbon content should be 0.18%. The materials selected for the study include AISI 1018. Table 1 gives the details of the chemical composition and Mechanical Properties of the material.

Table 2: Chemical Composition of AISI 1018

The aforementioned materials have low carbon content, hence can be welded easily. However, AISI 1018 alloy steel is selected as it has higher yield strength and strength to weight ratio than other materials.

Table 3: Comparison of Different Material

Availability is one of the main factors which dominate the material selection process. Working on this single list of different desirable and available material was prepared. Steel and aluminum alloys are always the choice most of the time. After reviewing mechanical properties, availability, cost and other significant factors, Steel AISI 1018 was selected. AISI 1018 grade is a versatile alloy with good atmospheric corrosion resistance, reasonable strength and thermal conductivity. It shows good overall combinations of strength, toughness and fatigue strength. The above table provides a comparison of available material.

Bending Stiffness

The bending stiffness of the chassis refers to the amount of force required to deflect the chassis from the side of the vehicle. The bending stiffness affects the amount of energy lost through the structure when accelerating. Thus, having a stiffer chassis will result in more energy being transferred to the wheels and the forward motion of the car. A chassis that has a good torsional stiffness also has adequate bending stiffness.

The bending stiffness and bending strength must be calculated about a neutral axis that gives the minimum values.

Bending stiffness is considered to be proportional to the product E*I

where,

E→ Modulus of elasticity,

I→ Second moment of area for the structural cross section

The Bending strength is given by equation: (????????*????*????)/????

Where,

Sy → Yield strength, C→ Distance from neutral axis to extreme fiber

VI. DESIGN AND ANALYSIS SOFTWARE SELECTION

CATIA V5R21 was the CAD software used for designing, ANSYS 21 was used to analyze the impact test and LOTUS for steering design. All specifications laid down by the rulebook are taken as the foremost concern while designing and selection of parts.

VII. FINITE ELEMENT ANALYSIS (FEA)

After completion of the design, the CAD model of chassis was analysed by using the Ansys student version. The five analyses for chassis are given below.

A. Longitudinal Torsion

For longitudinal torsion test first, we fixed the supports at the end of the chassis where the tires are connected to the chassis. Then, for the front side of the chassis where the tires are connected, we applied load on one side and we applied the same amount of load on the other side but in the opposite direction.

Copyright

Copyright © 2023 Yash Chikhalkar. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.