Roof Design

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. Because the earliest automobiles were designed in an era of horse-drawn carriages, early automobile roofs used similar materials and designs. A roof module is a complete top for a convertible. Such tops can be a soft top or a retractable hard top which is produced by specialized convertible top suppliers and supplied to the OEMs. The OEMs finally are completing their cars in their own production lines with these tops to a convertible. Depending on the OEM it is possible that these suppliers are working as a full-service vehicle supplier and are producing the complete cars are not full-service vehicle suppliers and are delivering just the top to the OEMs.

ROOF CRUSH TEST:

         Roof strength evaluations are conducted on a quasi-static test system manufactured by MGA Research Corporation. The system consists of an upright assembly and an attached loading head that can be fixed at varying heights from the ground and at pitch angles ranging from −5 to +5 degrees to accommodate testing on the driver or passenger side. The roll angle is permanently fixed at 25 degrees. Four hydraulic actuators control the movement of the platen along two linear guides. The entire system is mounted on a T-slot bed plate anchored to the floor of the test facility. Two I-beams are mounted on the bed plate perpendicular to the longitudinal axis of the platen. The vehicle, with the attached rocker panel support system, is placed on these beams.

The vehicle is adjusted so that:

      The longitudinal centreline of platen is within 10 mm of the initial roof contact point. The yaw angle of the vehicle relative to the longitudinal axis of the platen is 0 ± 0.5 degrees. The midpoint of the platen’s forward edge is 254 ± 10 mm beyond the most forward point of the roof (including the windshield trim if it overlaps the roof) lying on the vehicle’s longitudinal centreline. To minimize the potential for loading the edge of the platen during the test, there should be a minimum clearance of 150 mm between every point along the forward edge of the platen and the structurally significant body components, when measured normal to the platen’s face body components include the roof, roof pillars, and any glass(windshield, side windows, roof glass) but not the side mirrors, trim, removable roof rails, roof mounted antennas, and generally any component that consumers can remove. If the 150-mm clearance is not achieved, then the vehicle is moved rearward longitudinally until the 150-mm clearance is achieved at the front edge of the platen, or an equal measure of clearance (±20 mm) less than 150 mm at the front and rear edges of the platen. The pitch angle of the vehicle matches the on-road angle, while also accounting for any difference between the platen’s pitch angle and the nominal −5 degrees. The maximum combined difference of the vehicle and platen pitch angles from their targets is ±0.5 degrees. (For example, if the on-road vehicle pitch angle is −0.2 degrees and the platen pitch angle is −5.2 degrees, the target sill angle for the test is −0.4 ± 0.5 degrees.) If necessary to achieve this angle, shims are inserted between the rocker panel supports and the W10x88 I beams attached to the bed plate.

Master section of Front Roof Rail:

Master section of Rear Roof Rail:

Master section of Bow Roof Rail:

Master section of Centre Reinforcement Rail:

Master section of Centre Sun Roof Rail:

Objective:

                The project is to design a Front roof rail, bow roof rail, Centre roof rail (inner and outer), Rear roof rail and roof reinforcements from the styling surface received. After the design is done, heat load and snow load calculations will be done and Draft analysis.

Design Consideration:

                      Roof design used on NX CAD software from the given styling surface. Sheet thickness is considered as 0.75 mm for all components and clearance is 0.2mm. Depend on length consider to apply on Two bow roofs are provided for the more strength of the roof.    

• Front Roof Rail
• Bow Roof 1
• Bow Roof 2
• Centre Roof Rail (Inner Roof)
• Centre Roof Rail (Outer Roof)
• Rear Roof Rail

Front Roof Rail:

                Front Roof Rail which connects the wind shield glass body side outer and the inner panel. Here the front roof rail is designed based up on the master section given data follow the dimensional. Initial support of front roof rail outer roof rail. It is fixed to BIW with spot welds and roof surface is attached with the help of mastic sealants. Draft analysis five degree is also done on the section to check its manufacturing process.

Bow Roof Rail:

                Bow Roof is an additionally add reinforcement to improve the strength of the roof. It is fixed with roof body with mastic sealants. It is fixed to BIW with spot welds and outer roof surface. Presently in this project two bow roofs are added. If minimum length mean used on bow roof in case maximum length is to use on two or three the number of bow roof. Draft analysis five degree is also done on the section to check its manufacturing process. Distance between outer roof rail and inner roof rail 6.5mm. Overall length of centre roof rail is 75mm and angle is 7deg all edges. Draft analysis five degree is also done on the section to check its manufacturing process.

Bow Roof Rail 1:

Bow Roof Rail 2:

Central Roof Rail: (Inner and Outer Roof)

        Generally central roof rail is placed at the centre of the roof which is connected to the B-pillar support structure. This central roof rail helps in adding the strength to the roof. The cross section of this is more since it needs to provide more strength to the roof. Here both are ends are joined together using mastic sealants. To BIW by spot welds. Distance between outer roof rail and inner roof rail 6.5mm. Overall length of centre roof rail is 90mm and angle is 7deg all edges. Draft analysis five degree is also done on the section to check its manufacturing process.

Master section of Centre Reinforcement Rail:

Master section of Centre Sun Roof Rail:

                 To combine centre reinforcement rail and sun roof rail. Here both are ends are joined together using mastic sealants. To BIW by spot welds. Distance between outer roof rail and inner roof rail 7.25mm. Overall length of centre roof rail is 90mm and angle is 7deg all edges. Draft analysis five degree is also done on the section to check its manufacturing process.

Rear Roof Rail:

            Rear Roof Rail to joins the back door. It is the reinforcement provided at rear side of the roof. Backdoor and bodyside panels are attached with this part. It is also attached with mastic sealants and BIW by spot welds. Distance between outer roof rail and inner roof rail 6.5mm. Draft analysis five degree is also done on the section to check its manufacturing process.

Draft analysis:

Front Roof Rail:

Bow Roof Rail 1:

Bow Roof Rail 2:'

Central Roof Rail:

Rear Roof Rail:

Section Modulus of The Roof:

                       The section modulus (S) is geometric property of the cross section used for designing beams and flexural members. It does not represent anything physically.

Front Roof Rail:

Bow Roof Rail 1:

Bow Roof Rail 2:

Central Roof Rail:

Rear Roof Rail:

Roof Design:

Heat Distortion Curvature Study

             This study is done to check how the sheet metal components perform in the extreme heat conditions. Sheet metals have tendency to change its shape in high temperatures. To avoid any failure of sheet metal components this study is done to determine its capacity.

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

Judgement Condition: OK< 2.7> 3.1

Were, 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]

CALCULATIONS:

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 (t^2)] / [α x s x [(Rx + Ry)/2]^2 x 10^8]

Were

α = My* (Lx)^2*10^-12, My = Y(Ly-Y)

Judgement 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 centre point between Roof rail Front /Rear as the reference point of the front and the rear.

Lx = Distance between the Left and Right end of the roof on the Roof BOW [mm]

Width of the roof panel exposed on the surface.

Y = Distance 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]

CALCULATIONS:

CONCLUSION:

Hence the roof, front roof rail, bow roof rails, central roof rail and the rear roof rail is designed by following the master sections and the moment of inertia and draft analysis are carried out to check feasibility manufacturing.