Roof Design

Roof of Automobile Vehicles:

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.

ROOF CRUSH TEST :

Roof crush test is the design given by the IIHS ( insurance institute of highway safety ) . After analyzing the many accidents IIHS has then fixed some regulations , that how to perform the crush test .

IIHS gives the rating based up on this test . For this they consider two points while giving the rating

• How fast the car can reforms to its original shape after the roll over and
• How deep is the protrusion after the roll over
  
  

  GOAL OF ROOF CRUSH TEST :

  To minimize the protrusion into the occupant compartment , so that the seat belts and air bags can do there job in protecting the occupant

  CONDITIONS TO FOLLOW FOR ROOF CRUSH TEST :

  There are two conditions that should be followed for the roof crush test , they are

  INITIAL CONDITION :

  • Close and lock all the doors
  • Close all the windows

  SECOND CONDITION :

  Fix the body sill or chassis frame on a hard lever surface horizontally

  METHOD OF APPLYING THE FORCE :

  The load is applied in such a way that 50 is tilted from the front end to the rear end and the load will be in 1800 mm in length and 750 mm in width . The load is applied at the position of 250 from the flatness of the roof . The load is applied on the roof for almost 120 sec and the crush speed at which the load applied is 13 mm/sec or less than that

  
  
  
  
  
  
  
  
  
  
  Components used in the Roof design :
  
  

  • 1. OUTER ROOF
  • 2. FRONT ROOF RAIL
  • 3. BOW ROOF 1
  • 4. CENTER ROOF
  • 5. BOW ROOF 2
  • 6. REAR ROOF RAIL
    
    
    
    
    
    OUTER 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.
  
  
  
  
  
  

  • FRONT ROOF RAIL:

  Front roof rail is the one which joins the wind shield glass , body side outer and the inner panel also. Here the front roof rail is designed based up on the master section given
  
  

  • BOW ROOF :

  The bow roofs are give to improve the torsional stiffness and load bearing capacity of the roof structure . The number of bow roof present is depends on the overall size of the roof . Presently in this project two bow roofs are added.
  
  
  
  
  
  
  

  • CENTER ROOF :

  Central roof rail helps in providing effectively support to the flat area of the roof as it is more susceptible to failure under the action of load . generally central roof rail is placed at the center of the roof which is connected to the B-pillar support structure.This central roof rail helps in adding the strength to the roof during the rool- over test.
  
  
  
  
  

  REAR ROOF RAIL :

  Rear roof rail is the one which joins the back door and the body side outer

  
  
  
  
  ROOF OUTER PANEL:
  
  
  
  
  
  
  Roof With roof Rails :
  
  
  
  
  
  

  Bow–Roof Prediction Formula(Heat Distortion 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]

  Judgment Condition

  OK< 2.7

  Calculating the Heat Distortion criteria:--

  • To calculate the Heat distortion criteria, we have to take a note of few values and note it down.
  • To note down the values, first, we need to create a sketch.
  • Create a line at the center of the roof part in the 0-Y axis and then draw another line with a distance of 300mm to the O-Y line.
  • Now create lines at a distance of 100mm on both sides to the 300mm line.
  • Create a new sketch in which we need to Project the Roof Rails curves lines between the bow roofs and rails coming at the Edge. These lines need to be created in X-direction.
  • Using these Edge line create lines at a distance of 100mm on both sides.
  • Now To find Rx and Ry we have to take the intersection points and meassure them
  • so project the points on the surface and use Arc/Circle Command to meassure the curvature
  • Now since we got all the values for calculating the Heat Distortion, substitute these values to the below equation.
  • W=[1.73×10-3×L]+[1.85×10-8 ×R2t]+[1.10×10-3×l]-2.68">W=[1.73×10−3×L]+

  
  
  

  Calculating the Snow Load Criteria:

  • To calculate the Snow Load Criteria, we have to take a note of few values and note it down.
  • To note down the values, first, we need to create a sketch.
  • Create a line at the center of the roof part in the 0-Y axis.
  • Now using this O-Y line as a center create lines with a distance of 100 on both sides.
  • Create a new sketch in which we need to create lines between the bow roofs and rails coming at the center. These lines need to be created in X-direction.
  • Using these center line create lines at a distance of 100mm on both sides.
  • Now intersect sketch 1 (lines in Y-direction) and sketch 2(lines in X-direction). This result will give us some points where the lines (X & Y)are coinciding with each other.
  • Extract the required points and project them on the roof surface. Now using these points create a 3 point arc or circle and note the radius of the arc in the X direction as Rx">Rx and in the Y direction as Ry">Ry.
  • Now since we got all the values for calculating the Snow Load Criteria, substitute these values to the below equation.
  • Qr=Iy×t2α×s×[Rx+Ry2]2×10-8">Qr=Iy×t2α×s×[Rx+Ry2]2×10−8