Roof Design

Title- Design of Roof

Objectives-

1. For the Given Roof styling, Develop the essential flanges and reinforcements, provide appropriate dimensions, check for Draft analysis, and submit your section modulus report on the 0-Y section.
2. Start with the creation of a roof ditch area the tool opening angle is only 3 degrees.
3. Do a curvature study on the roof and perform calculations to determine the position of the Bow-roof

Introduction-

An automobile roof or car top is the portion of an automobile that sits above the passenger compartment, protecting the vehicle occupants from sun, wind, rain, and other external elements. Because the earliest automobiles were designed in an era of horse-drawn carriages, early automobile roofs used similar materials and designs.

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Types of Car roofs-

• Convertible roofs
• Hardtops
• Sunroofs
• T-tops
• Targa tops
• Vinyl roofs

Safety point of view vehicle's roof plays a very crucial role especially rollover kind of accident, in which the vehicle tips over onto its side of the roof. And vehicle rollover crashes are the cause of many fatalities and several head, neck, and spine trauma around the world. Therefore, passenger safety is also a very important parameter in front of OEMs. It is not only a marketing strategy but also it is an obligation stipulated by international standards that are now placed in several countries, as well as a governmental requirement.

Rollover crashes, especially in the country, are usually very destructive events. Vehicle damage often includes the deformation of the roof and its supporting structures. Head and neck injuries are common and associated with roof deformation. Strengthening the roof is suggested as an appropriate countermeasure for such injuries.

Types of Rollovers

1. Tripped-NHTSA data show that 95% of single-vehicle rollovers are tripped. This happens when a vehicle leaves the roadway and slides sideways, digging its tires into soft soil or striking an object such as a curb or guardrail. The high tripping force applied to the tires in these situations can cause the vehicle to roll over. E.g., Soft soil, Guardrail, Steep Slope
2. Un-Tripped -Un-tripped rollovers are less common than tripped rollovers, occurring less than 5% of the time, and mostly to top-heavy vehicles. Instead of an object serving as a tripping mechanism, un-tripped rollovers usually occur during high-speed collision avoidance manoeuvres.

For this reason, strength is a very important criterion for designing vehicle roofs.              

FMVSS 216 Roof crush standards-

FMVSS 216, Roof Crush Resistance, establishes strength requirements for the passenger compartment roof of passenger cars, multipurpose passenger vehicles, trucks, and buses with a GVWR of 2722 kilograms or less. The purpose of the standard is to reduce deaths and injuries due to the crushing of the roof into the passenger compartment in rollover accidents. The standard does not apply to school buses and passenger cars that conform to the dynamic rollover test requirements of FMVSS 208, Occupant Crash Protection, and S5.3 by means that require no action by passenger car occupants. It also does not apply to convertibles, except for optional compliance with the standard as an alternative to the rollover test requirements in S5.3 of FMVSS.

The prescribed static loading device is a rigid unyielding rectangular block 762 millimetres by 1,829 millimetres. It shall not move more than 127 millimetres to achieve the specified resistive load when applied to the forward edge of a vehicle’s roof – see Figures 1 and 2. The resistive load to be achieved is 1½ times the unloaded vehicle weight (UVW) of the test vehicle or 22,240 Newtons, whichever is less.

The force shall be applied in a downward direction perpendicular to the lower surface of the static loading device at a rate of not more than 13 millimetres per second until reaching the compliant resistive load. The test shall be completed within 120 seconds. The static loading device shall be guided throughout the test so that it moves, without rotation, in a straight line with its lower surface oriented as follows and as shown in Figures

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Following are the design considerations of the roof-

1. Visibility criteria
2. Head clearance
3. Heat distortion and snow load criteria
4. Draft analysis
5. Safety parameters

INPUT DATA FROM STYLING TEAM-

We will be having the following data which is provided by the styling team

1. A- the surface of the roof along with the railing rack

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2. Master sections for various rails

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a. Master section for Rear roof rail

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b. Master section for Front roof rail

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c. Master section for Centre roof rail

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d. Master section for bow roof rail

3. Design concept sheet which will have details of parts (e.g., Component name, the material of component, manufacturing details, thickness details, vehicle variant, etc)

DESIGN OF FRONT ROOF RAIL

For designing the front roof rail, we need to consider some parameters which are as discussed below

a. Visibility of the driver and passenger

We always keep in mind while designing the front roof we do not reduce the visibility available to the driver. While designing the front roof one must stick to the master section dimensions because a little change in dimension will have an impact on the visibility of the driver (e.g. small change in angular dimension will lead to a large change in linear dimension)

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b. Headroom

There should be enough space between the roof rail and the head position of the driver so that when an accident will happen head will not hit the front roof rail.

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5. DESIGN OF BOW ROOF RAILS

A bow roof is a sheet metal component used to add more structural strength to the roof. Based on the curvature of the roof bow roof is provided.

To justify the position of the bow roof there are two criteria are used-

a. Heat distortion criteria

b. Snow load criteria

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BOW ROOF 01

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                                                                           BOW ROOF 02

Bow roof rail calculations-

1. Heat Distortion calculations

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

 Judgment Condition: OK< 2> 3.1

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]

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Snow load criteria calculations

Snow load criteria are useful to justify the bow roof rail position in snowfall regions. Due to snowfall, snow will get collected on the top roof which will tend to bend the roof. The bow roof will be at such a position it will provide more strength to the roof against bending.

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

Note: The Qr value given over here is correct. There was a typo error in the formula given in the video.

Where

α = My x Lx2 x 10-12 , My = Y(Ly-Y)

Judgement condition = Qr ≥ 3.1

                250 ≤ s ≤ 380

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 centre point between Roof rail Front /Rear as the reference point of the front and the rear.

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

        Width of the roof panel 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

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DESIGN OF CENTER ROOF RAIL

 

Following the same design process as the front roof rail and master section we design the centre roof rail.

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DESIGN OF REAR ROOF RAIL

For designing the front roof rail, we need to consider some parameters which are

<!-- [if !supportLists]-->1)     <!--[endif]-->Opening and closing of back door

<!-- [if !supportLists]-->2)     <!--[endif]-->Drivers’ visibility for rear area.

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DRAFT ANALYSIS

FRONT ROOF RAIL

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BOW ROOF 01

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BOW ROOF 02

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CENTRE ROOF RAIL

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REAR ROOF RAIL

 

 

 

 

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ASSEMBLY IMAGE

 

 

CONCLUSION:-

 

<!-- [if !supportLists]-->1.    <!--[endif]-->Using all input data, we have successfully designed Ditch area flanges, Front roof rail, Bow roof rails 1&2, and Rear roof rail as per the requirement

<!-- [if !supportLists]-->2.    <!--[endif]-->As per heat distortion criteria we come to know all bow roof positions are OK

<!-- [if !supportLists]-->3.    <!--[endif]-->As per Snow load criteria we come to know there is improvement required

<!-- [if !supportLists]-->4.    <!--[endif]-->All roof rails draft analyses are found OK.