ABSTRACT
Recent, the foundation for the application of computers in the product development process is the development of models of products using computer-aided design (CAD).
Throughout the life cycle of engineering products, computers have a
prominent, often central role. In the process of product design and manufacture, this role is becoming increasingly important as competitive pressures call for improvement in product performance and quality, and for reductions in development time-scales. Computers assist design engineers to improve the productivity with which they carry out their work. Through simulation and analysis they allow the performance of a product to be evaluated before prototype is made. This project is used to develop a research with a title 'Design and Analysis Multi Purpose Vehicle (MPV) Chassis' by concerning with the fundamentals of modeling process by which designs are defined using computers, and with exploration of applications of CAD. CAD is use to produce a detail drawing, simulation and conduct some analysis to the design. The chassis is designed to be able to contain the various components of an MPV. It is also designed to hold the driver, and hence the safety of the chassis has to be a major aspect of the chassis design. The research of this study involved the application of reverse engineering in producing an MPV chassis. The main focus of this study is the methodology and the application of reverse engineering in a real situation of product development. The process will follow normal reverse engineering and design steps and procedure and also will look on ways to produce a new product by taking an existing part as a reference. In this study, the main property to be identified is a design process on how to design an MPV chassis.
ABSTRAK Pada masa kini, penggunaan komputer telah diaplikasikan di dalam proses pembangunan produk baru dengan menggunakan perisian rekabentuk. Komputer memainkan peranan yang amat penting di dalam kitar hayat kejuruteraan sesuatu produk. Di dalam proses merekabentuk dan pembuatan sesuatu produk, peranan komputer menjadi bertarnbah penting kerana dapat meningkatkan prestasi dan kualiti produk dan dapat menjimatkan masa pembangunan produk. Komputer telah mambantu para jurutera rekabentuk untuk meningkatkan produktiviti dimana komputer telah memudahkan kerja mereka. Melalui proses simulasi serta analisis, seorang jurutera dapat menyelesaikan masalah bagi sesuatu produk yang baru sebelum prototaip dibina. Projek ini dijalankan bertujuan untuk membangunkan kajian yang bertajuk 'Merekabentuk dan Menganalisis Casis Kenderaan Pelbagai Guna (MPV)' dengan kesemua proses merekabentuk model dilakukan melalui penggunaan komputer serta aplikasi perisian rekabentuk produk dan perisian kejuruteraan produk. Perisian rekabentuk digunakan untuk menghasilkan lukisan kejuruteraan, melakukan simulasi serta analisis untuk rekabentuk yang telah dihasilkan. Casis direkabentuk untuk b e h g s i sepenuhnya dimana dapat menyokong pelbagai komponen kenderaan pelbagai guna (MPV). Casis juga direkabentuk untuk membawa pemandu serta penurnpang dan sod keselamatan adalah perkara yang amat dititikberatkan di dalam rekabentuk casis. Kajian ini juga melibatkan aplikasi 'reverse engineering' di dalam proses pembangunan produk. Fokus utama di dalam projek ini ialah kaedah perlaksaan dan aplikasi 'reverse engineering' di dalam situasi sebenar pembagunan produk. Proses perlaksaan akan mengikuti langkah 'reverse engineering' serta prosedur rekabentuk dengan mengambil contoh produk di pasaran sebagai rujukan. Perkara utarna didalam projek ini adalah untuk mengenalpasti proses merekabentuk casis untuk kenderaan pelbagai guna (MPV).
2.2 Criteria of good chassis Any good chassis must do several things: 1. Be structurally sound in every way over the expected life of the vehicle and
beyond. This means nothing will ever break under normal conditions. 2. Maintain the suspension mounting locations so that handling is safe and consistent under high cornering and bump loads.
3. Support the body panels and other passenger components so that everything feels solid and has a long, reliable life. In the real world, few chassis designs will not meet the criteria of 1. Major structural failures, even in kit cars, ark rare. Most kit designers, even if they're not engineers, will overbuild naturally. The penalties for being wrong here are too great. The trouble is, some think that having a "strong" (no structural failures) chassis is enough. Structural stiffness is the basis of what we feel at the seat of our pants. It defines how a car handles, body integrity, and the overall feel of the car. Chassis stiffness separates a great car to drive from what is merely good; (ERA Chassis, 2000) Different basic chassis designs each have their own strengths and weaknesses. Every chassis is a compromise between weight, component size, vehicle intent, and ultimate cost. And even within a basic design method, strength and stiffness can vary significantly, depending on the details. There is no such thing as the ultimate method of construction for every car, because each car presents a different set of problems; (ERA Chassis, 2000)
2.3 Types of chassis 1. Backbone: The tunnel becomes a primary load bearing member. This is a
potentially fine design, and if we were building a new car from scratch, we would seriously consider a backbone. But, this is not a new car, it's a replica of a classic! Because it is designed around the original Ford engines (and we wanted our customers to have several different transmission choices), the bulk of a compatible structural tunnel was unacceptable, especially considering the passenger compartment was a fairly narrow one to begin with. A backbone would make it impossible to maintain the look of the original interior and engine compartment. It would also create servicing difficulties; (ERA Chassis, 2000) Restricted access
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Fig. 2.3.1 : Backbone type of chassis 2. Space frame: A true space frame has small tubes that are only in tension or compression - no bending or twisting loads. That means that each load bearing point must be supported in three dimensions. It is nearly impossible to build an efficient space frame around the body. The rockers are simply too shallow, and the tunnel shaped incorrectly to make a reasonably triangulated structure. It was difficult to build and a nightmare to fix. The "space fiame" chassis that is currently built for another replica simply uses smaller tubes, many carrying bending and torsion loads. Simply more complication without improvement. Consider - the bending stiffness of a tube increases the by the square of the diameter of the (equal-wall-thickness) tube, and the torsional stiffness by the cube of the diameter, while the weight goes up linearly. The bottom line is - sometimes better off with a large tube; (ERA Chassis, 2000)
Fig. 2.3.2: Space frame type of chassis 3. Monocoque: An airplane (with a stressed outside skin) is close to a true
monocoque. In the automotive world, it's time to compromise again. Generally, the interior panels are stressed, but the outside has an aerodynamic facade of 'glass or aluminum. Reinforcements are required at the suspension points where there are local high loads. With the rockers 10" high x 9" wide, the net result is an incredibly stiff structure; (ERA Chassis, 2000)
Fig. 2.3.3: Monocoque type of chassis 5. "Ladder" frame: The ladder fiame is a shorthand description of a twin-rail
chassis, typically made fiom round or rectangular tubing or channel. It can use straight or curved members, connected by two or more crossmembers. Body mounts are usually integral outriggers fiom the main rails, and suspension points can be well
or poorly integrated into the basic design. (ERA Chassis, 2000)
Fig. 2.3.4: "Ladder" fiame type of chassis An Original 289 chassis
The Shelby Daytona used a modified 289 chassis made into a tubular semi-backbone design to correct the extreme flex of the original design; (ERA Chassis, 2000)
Fig. 2.3.5: An Original 289 chassis type of chassis Daytona Chassis
The ERA chassis uses 4" x 3" x .125"W structural tubing in a complex design meant to take suspension and body loads efficiently, while maintaining the original look from outside and in the engine compartment. Roll bar, body and door mounting points are built into the basic design for maximum efficiency. There are 4 crossmembers plus an "X" member for maximum torsional stiffness.
6. Round vs. Rectangular frame rails: There has been a lot tossed around regarding whose chassis - and what kind of tubing - is "strongest." Factory Five is numerically the biggest exponent of round tubes, but many others have preceded them. We chose to use rectangular tubing in our chassis for several reasons: Under pure vertical bending load, 4" x 3" rectangular tubing is about 37% stiffer than an equal wall thickness 4" round tube. This is especially important because a roadster doesn't have a roof to stiffen the passenger compartment. Not only can we feel a lack of "solidness" with a flexible chassis. Our variable door gaps will also make latching unstable
- and even occasionally cause paint chipping as the doors meet the main
body! We can see below that transverse members have little effect on beam stiffness. We just add up the individual stiffnesses of the components. We also have an "X" member, acting as an additional longitudinal beam reinforcement and as two transverse members. A round tube chassis is extremely difficult to "X" brace; (ERA Chassis, 2000)
Fig. 2.3.6: Round vs. Rectangular type of chassis
2.4 Chassis Design and Materials The chassis is the framework of any vehicle. The suspension, steering, and drivetrain components are mounted to the chassis. The chassis has to be a strong and rigid platform to support the suspension components. The suspension system allows the wheels and tires to follow the contour of the road. The connections between the chassis, the suspension, and the drivetrain must be made of rubber to dampen noise, vibration, and harshness (NVH). The construction of today's vehicles requires the use of many different materials; (Davies. G., 2003)
2.4.1 Chassis Design A typical dictionary definition of chassis usually includes terms such as frame and machinery of a motor vehicle on which the body is supported. There are three basic designs used today: frame, unit-body, and space frame construction.
Frame Construction Frame construction usually consists of channel-shaped steel beams welded andlor fastened together. The frame of a vehicle supports all the "running gear" of the vehicle, including the engine, transmission, rear axle assembly (if rear-wheel drive), and all suspension components. This frame construction, referred to as full frame, is so complete that most vehicles can usually be driven without the body. Most trucks and larger rear-wheel drive cars
use a full fhme.There are many terms used to label or describe the frame of a vehicle, including:
Ladder Frame: This is a common name for a type of perimeter frame where the transverse (lateral) connecting members are straight across, as in figure below. When viewed with the body removed, the frame resembles a ladder. Most MPV's are constructed with a ladder-type b e ; (Davies. G., 2003)
