Roof Design

OBJECTIVE:

• Create an assembly by developing the essential flanges for the outer roof and creating the reinforcements for the given roof styling, .
• Provide appropriate dimensions and check for Draft analysis with a tool opening angle of 7 degrees.
• Do a curvature study on the roof and perform calculations to determine the position of the Bow-roofs.

ROOF:

A roof in a car is the uppermost part of the car that provides protection and cover to the passengers and the driver.

• It is typically made of metal or other sturdy materials and is designed to withstand the forces of wind, rain, and other weather elements.
• In addition to providing protection from the weather, the roof also contributes to the overall structural integrity of the car and helps to keep the occupants safe in the event of an accident.
• The roof of a car can take many different shapes and forms, depending on the design of the vehicle, and may be fixed or retractable, depending on the model.
• Its main functinality are
  • Protection from the elements: The roof provides shelter from rain, snow, sun, and other weather conditions, allowing passengers to stay dry and comfortable inside the car.
  • Structural support: The roof plays an important role in the structural integrity of the car, helping to distribute weight and maintain stability.
  • Safety: In the event of a collision or rollover, the roof provides protection to the occupants by preventing them from being ejected from the car or crushed by the weight of the vehicle.
  • Aerodynamics: The shape of the roof can impact the aerodynamics of the car, affecting its speed, fuel efficiency, and handling.
  • Style: The roof is a prominent feature of a car's exterior design, and can be customized to enhance the vehicle's appearance and appeal.

Types of Roof in Cars:

1. Hardtop roof - a solid roof made of metal or other rigid material that provides the most protection from the elements and noise.
2. Convertible roof - a retractable roof that can be folded back or removed entirely to allow for open-air driving.
3. Sunroof - a small, retractable panel in the roof that allows sunlight and fresh air to enter the car.
4. T-top roof - a roof that has two removable panels, creating an open area in the middle of the roof.
5. Panoramic roof - a large, fixed glass roof that provides a wide view of the sky and surroundings.
6. Moonroof - a type of sunroof that is made of tinted glass or a solid panel that can be opened or tilted to let in sunlight and fresh air.
7. Retractable hardtop roof - a type of convertible roof that is made of metal or hard material and can be electronically retracted and stored in the trunk.
8. Cabrio coach roof - a type of convertible roof that features a soft top that folds down and tucks into a compartment in the rear of the car.

Convertable Roof.

Sun Roof & Moon Roof

Panaromic Roof in different cars

Advantages and Disadvantages of Roof in Automobile & Car

There are many advantages and functionality uses of roof in car and in automobiles , here are the some main key points of them

1. Protection from the elements: The roof protects the occupants of the car from rain, snow, wind, and other weather conditions, providing a comfortable and safe driving experience.
2. Noise reduction: A solid roof can help to reduce noise levels inside the car, creating a quieter environment for passengers.
3. Safety: The roof is an important structural component of the car, providing support and protection in the event of a rollover or other accidents.
4. Aerodynamics: The shape of the roof can help to improve the car's aerodynamics, reducing drag and improving fuel efficiency.
5. Security: The roof provides a barrier between the occupants of the car and the outside world, helping to keep them safe from intruders or other external threats.
6. Style: The roof can be a key design element of the car, contributing to its overall appearance and style.

The roof in a car is an essential component that has several advantages and contributes to the overall comfort, safety, and performance of the vehicle. And along the advantages there are also disadvantages in the roof.

1. Reduced headroom: The roof can limit the amount of headroom inside the car, making it less comfortable for taller passengers.
2. Reduced visibility: Some types of roofs, such as those with a small sunroof or T-top, can obstruct the driver's view, making it more difficult to see the road.
3. Weight: The roof is a heavy component of the car, which can increase its overall weight and reduce fuel efficiency.
4. Maintenance: The roof may require regular maintenance, such as cleaning, to prevent damage or deterioration over time.
5. Cost: Some types of roofs, such as a convertible or panoramic roof, can be more expensive to install and maintain, increasing the cost of the car.
6. Vulnerability to damage: The roof can be vulnerable to damage from objects like tree branches, hail, or other debris, which can be expensive to repair or replace.

The disadvantages of a car roof may vary depending on the type of roof and the specific car model, these disadvantages are generally outweighed by the benefits that the roof provides, such as protection from the elements and increased safety.

The limitations of the roof in a car will depend on the specific type of roof and the needs and preferences of the driver. While there are some limitations to consider are,

• The limitations of the roof in a car can depend on the type of roof and the specific car model.
• Limited open-air driving: While some types of roofs, such as a convertible or sunroof, allow for open-air driving, they may not provide the same level of open-air experience as a completely topless car, such as a motorcycle or a convertible without a roof.
• Limited cargo space: Some types of roofs, such as a panoramic or sunroof, may reduce the available headroom or cargo space inside the car, limiting the amount of storage space available.
• Limited visibility: Depending on the type of roof and its design, it may obstruct the driver's view or limit the amount of natural light that enters the car.
• Limited customization: Some types of roofs, such as a hardtop roof, may be difficult or expensive to modify or customize, limiting the ability of the driver to personalize their car.
• Limited durability: The roof can be vulnerable to damage from objects like tree branches, hail, or other debris, which can be expensive to repair or replace.
• Limited practicality: Some types of roofs, such as a convertible or T-top roof, may not be as practical or suitable for everyday use as a solid hardtop roof.

Accessories and Other components that are added to the roof of car to improve its strength , functionality and increase its features. The majorly considerations are,

• Roof racks: Roof racks are designed to carry luggage, bicycles, kayaks, skis, or other equipment that may not fit inside the car. They can be installed on top of the car roof and secured in place using special clamps or brackets.
• Cargo boxes: Cargo boxes are similar to roof racks but provide an enclosed space for storing luggage or other items. They can be especially useful for camping trips, road trips, or other situations where additional storage space is needed.
• Roof baskets: Roof baskets are another type of roof-mounted storage accessory that can be used to carry bulky or oversized items, such as camping gear, coolers, or sports equipment.
• Roof tents: Roof tents are designed to be mounted on top of a car roof and provide a convenient and comfortable sleeping area for camping or outdoor adventures.
• Roof-mounted solar panels: Solar panels can be installed on top of a car roof to generate electricity and power various accessories, such as lights, refrigerators, or electronic devices.
• Wind deflectors: Wind deflectors are designed to reduce wind noise and turbulence when driving at high speeds, improving the aerodynamics of the car and enhancing fuel efficiency.
• Ski or snowboard racks: Ski or snowboard racks are designed to hold skis or snowboards securely on the roof of the car, providing a convenient way to transport winter sports equipment.
• Roof Lamps: These provide the lighting to the car interior of the passengers for the accessability in the low light conditions and in the night time.
• Air Ducts: The AC ducts are provided for the for the rear side of the car for the comport of the rear passengers.
• Handle Bars: for the offroad vehicles and camping vehicles have the supporting handle bars that provided for the safety purposes.
• Insulation Material: These are fiber material that is added to the roof that abbsorbs the surround noice and vibrations . it improves the NVH factor of the Car.
• Thermal Insulatior: These materials are used in the premium segment cars that to maintain the temparature and other factors that are suiatable for the passengers in the car. It Protects against the heat absorbtion and cold temparatures into the Car body.

Emboss on Roof

Racks and other mountings on roof

The strengthen components of the Roof are:

1. Support pillars: The support pillars are vertical columns that run from the floor of the car to the roof, providing structural support and improving the roof's strength and stability. The number of support pillars can vary depending on the type of car and the roof design.
2. Reinforcements: Reinforcements such as crossbars or braces can be added to the roof to improve its rigidity and reduce the risk of deformation or collapse in the event of a rollover accident.
3. Roof rails: Roof rails are horizontal bars that run from front to back on the roof, providing additional support and stability to the roof structure. They can also be used to attach roof racks, cargo boxes, or other accessories.
4. Welding: Welding is a process that is used to join metal pieces together, increasing the strength and durability of the roof structure.
5. Adhesives in Mastic Points: Adhesives can be used to bond metal pieces together, providing additional reinforcement and increasing the overall strength of the roof.
6. Advanced materials: Advanced materials such as high-strength steel or carbon fiber composites can be used to make the roof stronger and more resistant to damage.

The strength and durability of the roof are essential for protecting the driver and passengers in the event of an accident. By adding these elements, car manufacturers can improve the safety and performance of their vehicles.

Types of material used in Roof Design:

The materials used in car roofs can vary depending on the type of vehicle and the desired characteristics, such as strength, weight, and cost.the material used in car roof construction will depend on a variety of factors, including cost, performance, weight, and style. Car manufacturers will choose materials that provide the desired characteristics for their specific model, while also meeting safety and regulatory requirements, Some common materials used in car roof construction include:

1. Steel: Steel is a strong and durable material that is commonly used in car roof construction. It is relatively inexpensive and can be easily formed into different shapes and sizes.
2. Aluminum: Aluminum is a lightweight material that is often used in high-end cars or sports cars to reduce weight and improve fuel efficiency. It is more expensive than steel but provides excellent strength-to-weight ratio.
3. Carbon fiber: Carbon fiber is a lightweight and high-strength material that is commonly used in high-performance cars or luxury vehicles. It is more expensive than steel or aluminum but provides excellent strength and stiffness while reducing weight.
4. Plastic: Some car roofs are made of plastic materials, such as polycarbonate or acrylic. Plastic roofs are lightweight, inexpensive, and can be molded into different shapes and sizes.
5. Glass: Glass roofs are also becoming increasingly popular in modern cars. They provide a panoramic view and can be tinted to reduce glare and heat. Glass roofs can be made of tempered glass or laminated glass for added safety and security.

Design Regulations:

The design of car roofs is regulated by various safety standards and regulations to ensure that they provide adequate protection for the occupants in the event of a rollover accident. The car manufacturers must ensure that their vehicles meet these regulations and standards to that their cars can provide adequate protection for occupants in the event of a rollover accident. Failure to meet these requirements can result in damage to a company's reputation and safety standarts along as the Trust of customers. Some of the key regulations governing car roof design are,

1. Federal Motor Vehicle Safety Standard (FMVSS) 216: This standard sets minimum requirements for roof crush resistance in the event of a rollover accident. It specifies the maximum force that a roof can withstand before it deforms or collapses and requires car manufacturers to test their vehicles to ensure compliance.

2. European Union (EU) General Safety Regulation: The EU General Safety Regulation sets requirements for various safety features in cars, including roof strength. It requires cars to meet a minimum level of roof strength to protect occupants in the event of a rollover accident.

3. United Nations Economic Commission for Europe (UNECE) Regulation 29: This regulation sets minimum requirements for roof strength and requires car manufacturers to test their vehicles to ensure compliance.

4. National Highway Traffic Safety Administration (NHTSA) Rollover Resistance Rating: The NHTSA provides rollover resistance ratings for cars, which take into account factors such as the vehicle's center of gravity, width, and height. These ratings can provide consumers with information about a car's likelihood of rolling over in the event of an accident.

There are the some crash tests , load bearing tests, Non destruction tests are also performed.

Design of Roof

• Roof of the the car is designed as per the master sections provided on it.
• The Rail bars are the provided to the roof pannel to provide the additional strength to the Roof outer pannel and for the crash test period.
• These rails are also provides the support the car body on the rolling condition and crash time.
• The rails mainly provided are Front rail , Rear rail, Bow rail, Center rails.
  • Front Rails : These are attached to the A piller of the car and along with the front glass and weather strip on it.
  • Rear Rails : These are the attached to the C or D pillar of the car and it is attached the Rear mirror and some card it is with back door also.
  • Bow Rails : These are the Additional bars that are provided bottom of the roof attached by the mastic sealent and spot welded on the edges. These are usually 2 to 3 are provided based on the length and curvature of the roof design. Some cars have the only one bow roof on it.
  • Center Rails : These are the main bar that is attached the B-pillar of the car body , it gives the strength to the complete car roof as it is mostly middle of the Car. in some cases it is additionaly supported by the Reinforcements.
• There are the limitation of the rails in the height of it. If the height of the rail is large then it effect visibility section of the driver and also arrests the head room and touches the passengers.
• The emboss and mastic points are provied for the strengthen of the rails and as well as the roof component.
• The Roof is designed as per the Mastersections provided , There are two tests to be done for the Roof for the Heat distortion and snow load critearia.
• The draft analysis is also performed on the roof and the rails and components with the minimum draft angle of 7deg, Weather the components and parts are manufacturable or not.
  • Heat Distortion: It is the test need to be performed on the car because, when the car is in outside locations , it gets heted up and tends to be the roof surface maliable and bends. To check its strength the caliculation is be done and verify the design of roof sets with in the range or not.
  • Snow Load Condition: In the Westren , Europian and some hill area od India there is Snow fall , the snow that deposits on the roof of the car is adding the additional weight to it and act for the longer duration which leads to the deformation of roof. We need to check the roof that withstands the load.
  • If these tests are fails then we need to consider the remedy and the alternative option that gives the additional strength of the Roof design.

Master sections provided for Roof Rails

Heat Distortion :

W = [1.73 x 10^(-3) x L] + [1.85 x 10^(-8) x (R^2)/t] + [ 1.10x10^(-3) x l] - 2.68

Where,

L = Roof Length in X-Direction[mm](Roof dimension in 0-Y)

R = Roof curvature

R = 2(Rx*Ry)/(Rx+Ry)

Rx = X curvature

Ry = Y curvature

t = Roof plate thickness [mm]

l = Bow Roof Span [mm]

Judgment Condition OK< 2.7

SECTION TYPE	RX (mm)	RY (mm)	R(mm)	L (mm)	t (mm)	l (mm)	W	Condition Statement
FRONT RAIL TO BOW RAIL 1	5636.8429	3350.1101	4202.546588	2023.5538	0.75	596.42	1.712295378	Pass
BOW RAIL 1 TO CENTER RAIL	4619.8706	7619.2526	5752.039669	2023.5538	0.75	325.9742	1.620465832	Pass
CENTER RAIL TO BOW RAIL 2	3872.7598	11112.5814	5743.794278	2023.5538	0.75	311.7155	1.603517427	Pass
BOW RAIL 2 TO REAR RAIL	3308.947	14399.4131	5381.288218	2023.5538	0.75	316.7117	1.555241116	Pass

Snow Load Prediction Formula

Qr = [Iy x t²] / [α x s x [(Rx + Ry)/2]² x 10^-8]

Note: The Qr value given over here is correct.

α = My x Lx² x 10^-12 , My = Y(Ly-Y)

t = Roof plate thickness [mm]

Ly = Distance between the front and rear roof Rails on the Vehicle along with 0Y[mm]

Length of Roof panel with the center point between Roof rail Front /Rear as the front and rear reference point.

Lx = Distance between the Left and Right end of the roof on the Roof BOW [mm]

The width of the roof panel is exposed on the surface.

Y = Distance front Front Roof Rail to Roof BOW[mm]

s = Distance for which Roof BOW bears divided load [mm]

s = L1/2 + L2/2

Iy = Geometrical moment of inertia of Roof BOW (Y cross-section )[mm4]

Rx = Lateral direction curvature radius of roof panel Y cross-section on Roof BOW [mm]

Roof panel curvature Radius of the Length Lx in Front view

Ry = Longitudinal Direction curvature radius of the Roof panel X cross-section on Roof BOW [mm]

Roof panel X curvature radius of length s in Side view

Judgment condition

1. Qr ≥ 3.1
2. 250 ≤ s ≤ 380

Section modulus

CONDIION	Ix (mm^4)	t (mm)	Rx (mm)	Ry (mm)	L1 (mm)	L2 (mm)	Lx (mm)	Ly (mm)	Y (mm)	S (mm)	Qr	Judgement Condition
FRONT RAIL TO BOW RAIL 1	1043.610747	0.75	6036.2314	2209.3278	690.5915	406.945	1085	1935.9262	690.5919	548.76825	0.621619958	Fail
BOW RAIL 1 TO CENTER RAIL	1218.36184	0.75	5502.5872	52564.443	406.945	392.6425	1060.2	1935.9262	1097.5368	399.79375	0.019661792	Fail
CENTER RAIL TO BOW RAIL 2	1049.196347	0.75	6384.3085	97693.4674	392.6425	445.7469	1045.4	1935.9262	1490.1793	419.1947	0.007161692	Fail

Draft Analysis & Component parts

Roof Outer Pannel

Front roof rail:

Center Roof Rail:

Bow Roof Rail 1:

Bow Roof Rail 2 :

Rear Roof Rail:

Roof Assembly

Analysis & Conclusion :

Here the test results of the Roof Design in the Heat Distortion and Snow load criteria is performed and it passes the Heat Distortion in all conditions and fails in the Snow load conditions . so that the Emboss are provided in the outer roof pannels to provide the adittional strength to it. The Emboss are provided in the Flat surface of the Front and Rear roof rails for the additional support.