Roof Design
Roof Design
AIM:
To develop the essential flanges and reinforcements with appropriate dimensions and checking draft by performing draft analysis, calculating section inertia, heat distortion and snow load on the roof.
ROOF
An automobile roof or car top is the portion of an automobile that sits above the passenger compartment, protecting the vechicle occupants from sun, wind, rain, and other uncontrol moments. In later years, many variations on the automobil roof developed.
COMPONENTS OF ROOF:
A car roof is a complex assembly of different element helping it to achieve the safety requirements established by various automotive regulatory bodies arount the world. Roof consists of structural members:
1. Outer roof panel
2. Front roof rail
3. Rear roof rail
4. Center roof rail
5. Bow roof rail 1
6. Bow roof rail 2
OUTER ROOF PANEL
The outer roof panel skin is given we need to create flanges. And give 0.75mm thickness and given a emboss to give strength for outer roof panel.
FRONT ROOF RAIL:
Front roof is very importon point to strength give to roof. Front roof design is followed by given master section. And give a 0.75mm thickness solid part.
RARE ROOF RAIL:
The Rear roof rail is give the strendth to the rear side of the roof its main function is to give strength to the roof. Also the back door rests on the rear roof rail. Its also joined the given roof using mastic section. With 0.75mm thickness of solid part.
CENTER ROOF RAIL
Center roof rail is center of the roof to give additional strangth with B piller and it also help to roof of the ends to used to connect with spot welded of flanges. Its created with given master section. And 0.75mm thickness for solid part.
BOW ROOF RAIL 1 AND 2:
Bow roof rail is an additional to avoid roof bend and increase the strength of roof. This bow roof is created by given master section with 5mm distance between with bow roof to outer panel. Both edges will spot welded with flange with 0.75mm thickness solid part.
DRAFT ANALYSIS:
The draft analysis is helps to analysis the all surface to check and currect the mistakes.
BOW-ROOF PREDICTION FORMULA:
RX and RY MESUREMENTS:
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
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. There was a typo error in the formula given in the video.
Where,
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
Qr ≥ 3.1
250 ≤ s ≤ 380
FRONT VIEW
ISOMETRIC VIEW
SIDE VIEW
TOP VIEW
CONCLUSION:
To pass the bow-roof prediction formula, W=<2.7 and to snow load formuls, Qr>3.1. failimg to meet these requirements symbolise that the roof does not has strength to with stand thermal and physical load and hence may lead to permanent deformation.
From the above data we can see the roof, To increase the strength of outer roof panel, creat large embosses. It not only helps to improving the structural propertied, but sometimes also help to improvement performance of the cars.