Roof Design

Aim: For the given roof styling, develop the essential flanges and reinforcements, provide appropriate dimensions and check for draft analysis and to perform roof curvature study

INTRODECTION:

ROOF

An automobile roof or car top is the portion of an automobile that sits above the passenger compartment, protecting the vehicle occupants from:

• Protecting from weather (Sun, Wind, Rain) and another external element.
• The important role in the roof is safety (in case of roll-over accidents).

Reinforcement:

If the roof is flat surface it will be very weak and cannot be able to with stand the forces like snow in order to increase the strength of the roof these reinforcements like front roof rail central roof rail and the bow roofs are introduced and joined to the flat surface of the roof wit different join process

The required tool opening angle is minimum 3 Degrees.

Factors which are considered before creatin Ditch area.

Headroom clearance

Visibility criteria

Back door assembly

Windshield assembly

BOW-ROOF PREDICTION FORMULA

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]

JUDMENT CONDITIONS

CASE	L	RX	RY	R	l	T	W	RESULT
FRR-BR1	2032.85	5740.02	202.259	390.7493085	375.267	0.75	1.253390431	PASS
BR1-CRR	2032.85	6150.236	4982.952	5505.400749	434.625	0.75	2.062550789	PASS
CRR-BR2	2032.85	10133.19	4065.43	5802.78571	332.446	0.75	2.033105043	PASS
BR2-RRR	2032.85	14223.965	3334.918	5403.049489	452.779	0.75	2.054980013	PASS

SNOW LOAD CRITERIA

This test is done to know how the roof behaves when there is snow over. Normally due to the snow weight the dent will happen. But the roof should be designed in such a way that when the snow is removal the roof should go it its original position. These are the basic requirements for snow load criteria.

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

10 = 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

ROOF RAILS	ly(mm)	Lx (mm)	Ly (mm)	L1(mm)	L2(mm)	Rx(mm)	Ry (mm)	t(mm)	Y(mm)	s	My	α	Q	RESULT
FR-BOW 1	190.608	1075.253	2032.46	445.28	419.65	4357.37	2875.2	0.75	1434.48	422.4	860089.1	0.993432	20.75	PASS
BOW1-CRR	456.98	1062.96	2032.46	419.56	319.8	379.4	6705.34	0.75	514.14	369.65	779541.14	0.871905	13.81	PASS
CRR-BOW2	220.78	1055.28	2032.46	318.52	289.25	4310.106	11249.6	0.75	424.5	309.5	670135.11	0.746125	7.81	PASS

Front Roof Rail

The front roof rail is located on the front of the roof where the wind shield joins with the roof. The visibility criteria and the head room clearance of the passenger are taken into consideration for the bottom flange. One end of the rail is joined using spot welding while the other end is joined with the roof using mastic sealants for increased strength.

Bow roof 1

Bow roof is an additional stiffening member for the roof to increase the strength and so that it can satisfy the norms. Both the ends are joined together using mastic sealants to increase strength and since this would not affect the styling of the roof.

Centre Roof Rail

Centre Roof rail or the reinforcement center is located at the center of the roof. The cross section of this is more since it needs to provide more strength to the roof. Here both ends are joined together using mastic sealants.

Bow roof 2

This bow roof also has the same purpose as that of the first one. This one is located between the center bow roof and rear roof rail.

Here one end is joined using spot welding while the other end is joined using mastic sealants.

Rear Roof Rail

This roof rail joins the back door and the roof. Inputs from the backdoor are taken into consideration for designing this roof rail.