Design of Automotive Roof
Roof Design
Objective:
- Creating the ditch area
- Doing a curvature study on the roof and perform calculations to determine the position of the Bow-roof
- To perform section modulus analysis
- To perform draft analysis
Design considerations:
- Head clearance
- Visibility
- Curvature study
- Material Thickness
- Heat distortion and snow load criteria
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. It shields the passenger compartment with connections to body side and roof reinforcements which includes front, center and rear rail roofs with 1 or 2 bow roofs depending upon the length of the vehicle.
The main components of an automotive roof:
1.Front roof rail: It is the roof reinforcement near the A-pillar and front region of the car. The opening angle is kept at 3 degrees and following master section is followed to develop the reinforcement. Thickness of 0.65mm is maintained. A gap of 2mm is provided on the left most side for provision of headliner. It can have provision for front cabin lamp.
2. Bow roofs 1 and 2: They provide extra support from roof bending and one of important structure to prevent roof crush and rollover tests. Mastic sealant provisions are given on bow roofs where spot welding is not possible and also mastics improve strength locally and reduce the NVH. Thickness of 0.65 mm is maintained.
3.Center roof rail: Center roof rail supports the roof and B-pillar together and is one of the most important structure to carry the weight of the roof being at the center. Thickness of 1.5mm is maintained. The following master section was used to develop center roof rail. Emboss is given to improve strength locally.
4.Rear roof rail: It is located near the rear end of the car. Thickness of 0.65mm is maintained. The following master section was used to develop rear roof rail.
Draft analysis:
The draft analysis of all members is done at 3 degrees.
Theoretical prediction of positioning bow roofs:
1. Heat distortion criteria:
In order to verify the value of W is within the limits following formula is used:
The following information has been captured for calculation of W value:
As we can see W value is less than 2.7 mm the heat distortion criteria is satisfied.
2.Snow load criteria:
This evaluation is performed in cold regions where snow occurs. Roof design must pass through these calculations to ensure that it has sufficient stiffness to withstand the load due to accumulation of snow over the roof.
The formula for snow load is given by:
For calculating the value of Qr following info has been captured:
As we can see that the value of Qr is less than 3.1, its a NG condition which means we can either send feedback to styling team to change the radius of curvature near that section or move the bow roof so that the value of Qr is greater than or equal to 3.1.
Conclusion:
Thus from the roof design challenge, I have understood the design methodology and also understood various theoretical prediction formulas for positioning of Bow roofs.
Drive link for the model:
https://drive.google.com/open?id=17Bj8n93tyHzMY599dD3higDKtPPDD6EM