Roof challenge
Roof
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.
Objective:
1. To design the car roof for which using the given input models.
2. Calculation for Heat Distorsion & SNOW LOAD CALCULATION is done wheather to check and withstand the standards,
Significant of design consideration are:
1. Visible criteria,
2. Head clearance,
3. Curvature Study
4. Heat Distortion and snow load criteria
5. Draft analysis.
Final Roof Design:
Isometric View (Outer Panel)
Front Roof Rail
The Front roof rail is the front part of the roof. It is designed considering the driver's visibility criteria. One end is joined using spot welding and other end is joined using mastics.
Bow Roof -1
The bow roof is a stiffner part which gives strength to the roof.
Center Roof:
The Center roof is the center most part in the roof it gives strength to the roof . It is located connecting the B Pillar. The Center roof is joined with the help of mastrics.
Reinforcement - Gives strengthen to Center Roof.
Center Roof and Reinforcemet.
Bow Roof 2 - It is stiffner part which gives strength to the roof.
Rear Roof Rail:
The Rear roof is joined with the back door of the roof. It is designed with the design consideration of the back door design.
Outer panel with rear roof rail:
Calculation for heat Distorsion.
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< 2.7
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]
Calculation of heat distorsion criteria(Rx)
Calculation of heat distorsion criteria(Ry)
I (value)
Calculation of Heat Distorsion
| Calculations for Heat Distorsion | ||||||||
| BOWS | RX | RY | I | L | T | R | W | OK/NG |
| FR - BR 1 | 5781.664 | 2375.548 | 374.364 | 2049.799 | 0.75 | 3367.479073 | 1.382846887 | OK |
| BR 1 - CR | 4916.735 | 6307.252 | 400.133 | 2049.799 | 0.75 | 5525.859334 | 1.588748443 | OK |
| CR - BR 2 | 3979.215 | 10503.134 | 399.799 | 2049.799 | 0.75 | 5771.747161 | 1.614077024 | OK |
| BR 2 - RR | 3248.617 | 2994.918 | 334.557 | 2049.799 | 0.75 | 3116.613114 | 1.324012785 | OK |
Calculation of 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)
Judgment 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 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
Snow load criteria
Moment of Inertia
Bow Roof 1 Moment of Inertia
Center Roof Moment of Inertia
Bow Roof 2 Moment of Inertia
| SNOW LOAD CALCULATION | ||||||||||||||
| BOWS | Iy | Y | Lx | Ly | L1 | L2 | My | Alpha | S | Rx | Ry | t | Qr | Determination |
| FR - BR 1 | 465.9 | 514.059 | 1203.728 | 2049.799 | 514.059 | 482.274 | 789460.9687 | 1.143898232 | 498.1665 | 4528.939 | 2603.06 | 0.75 | 3.616519185 | OK |
| BR 1 - CR | 2289 | 482.274 | 1152.198 | 2049.799 | 482.274 | 482.881 | 755976.5519 | 1.003604406 | 482.5775 | 3767.51 | 6171.07 | 0.75 | 10.7658917 | OK |
| CR- BR 2 | 745.6 | 482.881 | 1124.392 | 2049.799 | 482.881 | 511.379 | 756634.9308 | 0.9565812874 | 497.13 | 4270.192 | 11007.356 | 0.75 | 1.51143422 | NG |
| BR 2- RF | 511.379 | 1110.111 | 2049.799 | 511.379 | 786715.6812 | 0.969506263 | 255.6895 | 4031.211 | 16249.609 | 0.75 | 0 |
The snow load criteria is achieved (CR-BR2 - only gets low value otherwise all ok.)
Conclusion:
We were successfully able to design the roof with all the roof rails for better support and strength. We designed it so as to satisfy the norms and regulations by calculating the heat distortion criteria and the snow load criteria. While doing this we also understood about the methodology behind designing the roof of the car and what all we take into consideration while designing so.