Roof Design

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.

The Automobile roof consists of the following parts:

• The outer panel
• Front roof Rail
• Bow Roof
• Centre Roof Rail
• Rear Roof Rail
  
  

  FRONT ROOF RAIL:

  The front roof rail is created at the front side of the roof to provide strength to the roof. Headroom clearance and the driver visibility are the two important factors to be considered while designing the front roof rail. the front roof rail is connected to the roof outer panel with the help of mastic seal.

  
  
  
  

  BOW ROOF:

  It is used to give strength to the area between the front roof and the centre roof rail. Also it is created in the area between the centre roof rail and the rear roof rail to provide enough strength. It can be created in any numbers depending upon the roof length but the position of the bow roofs is to be justified by curvature study.

  
  
  
  

  CENTRE ROOF RAIL:

  It is created at the centre of the roof. It is connected to the roof by mastic seal.
  
  
  
  
  

  REAR ROOF RAIL:

  It is created at the rear end of the roof. The fitment of the backdoor is to be considered while designing the rear roof rail.
  
  
  
  
  
  
  Moment of inertia-
  
  1.Front roof Rail -
  
  
  
  2.Bow roof 1-
  
  
  
  
  3.Centre bow roof-
  
  
  
  
  4.Bow roof 2-
  
  
  
  
  
  5.Rear Roof Rail-
  
  
  
  
  
  
  

  Draft analysis-

  Before we give the part for manufacturing we have to some analysis ourself to check all the constraints and to check if we have any negative draft on a part .
  
  
  Front roof rail-
  

  
  Bow roof 1-
  
  
  
  Centre roof rail-
  
  
  
  Bow roof 2-
  
  
  
  Rear roof rail-
  
  
  
  Roof-
  
  
  
  
  

  Heat Distortion Curvature Study-

  This study is used to find out and predict the heat distortion temperature at where the material starts to soften when exposed to a fixed load. So in order to avoid bending or damage of the roof based on this calculation we will decide the position on the roof bows on the roof.
  
  
  

  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 Criteria-

  We predict the snow load in this of the roof bows and then place and change the design of the load accordingly to satisfy the condition.
  
  
  

  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