Page 1

A MODULAR AUTOMOTIVE ROOF SYSTEM DESIGN CONCEPT BASED ON POLYURETHANE COMPOSITE TECHNOLOGY

D. Stratton, P. Platte and D. Rocco, Bayer MaterialScience LLC

Abstract

There is a growing trend in the automotive industry to offer more “non-traditional” roof configurations to the consumer. In many cases the non-traditional roof contains glass, guides, drives and other hardware that increase the cost and weight of the vehicle. Consequently, suppliers are being challenged to offer designs that use lightweight materials, integrate or eliminate components, while maintaining or improving overall structural and dimensional performance of the vehicle. Based on a standard "body in white" roof structure, the innovative concepts described in this paper use molded polymers and composite materials that allow a vehicle to be fitted with a wide variety of roof “modules”, each having customized performance, content and value. The modules are designed to integrate components, eliminate post painting, increasing vehicle rigidity, and reduce weight. Conceptual designs illustrated in this paper will include two different vehicle architectures and two different roof module constructions. Three different composite materials will be reviewed for their suitability in the roof module. Detailed section views are included to illustrate important part design features, attachment methods, performance considerations, and general composite “know-how”. The concept’s value proposition is examined in four areas: cost, weight, safety and assembly. Technical and economic benefits to the value proposition include weight reduction, design and styling freedom, in-mold features, attachment points, color options, fixed or moveable window design, and improved roll-over safety due to the lowered center of gravity. Since the modular roof system starts with a component that is ready to assemble it offers a path forward for the supply chain, which enables OEMs to decrease capital expenditures and reduce labor hours required to manufacture a vehicle. The backbone of the value proposition is a recently conducted case study, comparing a traditional vehicle to the same vehicle fitted with a composite polyurethane roof module. The two piece roof module examined in the case study is constructed using long fiber technology, and results in a vehicle that is lighter, stiffer, has a lower center of gravity, while offering greater design freedom and integration flexibility than traditional roof materials and design solutions. In addition to polyurethane composites, the paper includes references to adhesives, coatings, co-extruded polycarbonate and polycarbonate/acrylonitrile film, and polycarbonate thermoplastic glazing.

Page 2

Background

In 2005, in response to the growing trend in the automotive industry to offer more “non-traditional” roof configurations to the consumer, Bayer MaterialScience (BMS) introduced a basic modular roof frame design concept. It was for a generic medium-sized vehicle that could be manufactured in three variations: a base roof, a sunroof, or panoramic roof module. Each variation could be made with single, double, or triple panel versions. It was concluded materials and process technologies to implement an integrated roof module on a production scale were available. A commitment was made to further develop engineering solutions and knowledge toward polyurethane composites for roof system structural components [1]. New roof system polyurethane composite structural components are in production. The Opel Zafira roof manufactured by Webasto in Europe is made from BMS Baydur polyurethane composite (PUR) with the long fiber technology (LFT) processed behind a polycarbonate (PC) based film [2]. It is a Class “A” finished module ready for assembly by the automotive original equipment manufacturer (OEM). This application is a good example of the emerging material and design technology based on PUR composites and PC film that enable component integration, eliminate post painting, increase vehicle rigidity, reduce weight, and improve vehicle safety. Figure 1 shows an exterior view of the Zafira. Figure two shows the roof from an interior perspective.

Figure 1: Opel Zafira (photo courtesy Opel) Figure 2: Zafira Roof Module (photo courtesy Opel) Encouraged by the industry trend and commercial implementation, Bayer furthered its design initiative by establishing two different architectures and two different roof module design constructions. Three different composite materials were reviewed for their suitability. Detailed section views were developed to illustrate important part design features, attachment methods, performance considerations, and general composite knowledge. The concept’s value proposition was also developed and examined in four areas: cost, weight, safety and assembly. Technical and economic benefits to the value proposition include weight reduction, design and styling freedom, in-mold features, attachment points, color options, fixed or moveable window design, and improved roll-over safety due to the lowered center of gravity. The backbone of the value proposition is a recently conducted case study, comparing a traditional vehicle to the same vehicle fitted with a composite polyurethane roof module. The two piece roof module examined in the case study is constructed using LFT, and results in a vehicle that is lighter, stiffer, has a lower center of gravity, while offering greater design freedom and integration flexibility than traditional roof materials and design solutions.

Page 3

Architectures & Design Concepts Fundamental assumptions were developed and used as the basis for the new “non-traditional” roof concept:

• The roof module is provided “whole” by a tier-one supplier or system integrator • The module drops onto the roof frame, aligns using dowel pins, and is attached permanently

using glue • If different car platforms use the same roof system they can use the same modules • The modules can have any glazing style: none, panoramic, fixed, moving, etc. • The module integrates typical passenger compartment options: dome light, HVAC, sun shade,

electronics, air bags, etc. • The module is supplied to the OEM with the headliner attached • The OEM must provide “trim” pieces of headliner to finish the perimeter of the interior (outboard

of the roof module) • The trim pieces can be installed before the roof module, possibly from outside/above • The roof frame must be re-designed as part of this roof system

Figure 3 depicts the “traditional” roof systems that consists of a sheet metal roof skin spot welded to the roof frame and to cross-car braces. In this system the roof is installed before e-coating or painting.

a Traditional Roofsheet metal roof skin,spot welded to roof frame and to cross-car braces, installed before E-coating or painting

Bayer Concept

Bayer Concept

Figure 3: Traditional Roof System Definition (Bayer MaterialScience) Figure 4 shows a “traditional” roof frame structure featuring conventional geometry standard on a production SUV. This structure was used as the baseline upon which to develop the two basic architectural approaches for the “non-traditional” concept.

Page 4

conventional (baseline) roof frame geometry is a standard production SUV roof frame

Figure 4: Traditional Roof Frame Structure The first “non-traditional” architectural approach was named “Over-the-Top” because the roof module overlaps the roof frame. The second approach is named “Recessed” because the roof module fits into the roof frame opening. Figure 5 illustrates the two basic architectural approaches designed to offer the OEMs design and styling choices.

“Over-The-Top”(roof module overlaps roof frame)

“Recessed ”(roof module fits into roof frame opening)

Gives OEM Design/Styling Choices

Bayer ConceptBayer Concept

*Bayer Concept*Bayer Concept

Figure 5: Two Basic Architectural Approaches

Page 5

Figures 6 and 7 show details of the respective approaches and illustrate how the module appears when installed. Cross-sections A, B and C show the detail for the side, front header and rear header, respectively.

A

ACC

B B

module installed

Section A-Adoor

Section C-C

hatch back

Section B-B

windshield

roof module placed on top of roof frame

*Bayer Concept*Bayer Concept

Figure 6: “Over-the-Top” Architectural Approach

A

A

CC

B B

module installed

Section A-Adoor

Section C-C

hatch back

Section B-Bwindshield

roof module fits into roof frame opening

*Bayer Concept*Bayer Concept

Figure 7: “Recessed” Architectural Approach

Page 6

The concept involved offering two design options for either architecture. One option consisted of a single molded part and was named “One Piece Design”. The other option consisted of two molded parts glued together and was named the “Clam-shell Design.” Figure 8 illustrates the design options that could be used with either architecture.

“One Piece Design”single molded part

“Clam-shell Design”two molded parts glued together

either roof architecture approach can have the following (2) design options

*Bayer Concept*Bayer Concept Figure 8: Roof Module Design Options

Advantages of the “One Piece Design” include:

• The composite polyurethane substrate can be molded between the paint film and the headliner cloth in a single molding process, eliminating fasteners and reducing assembly steps.

• A perimeter seal can be molded onto the above, which will simultaneously seal the edges of the composite material, and provide sealing against the car body (roof line)

• Integration of assembled parts: dome light, wiring, etc. is possible • Simple design concept • Light weight, but stiff construction • Potential increase in vehicle rigidity & torsion • Potential increase in roll over resistance • Reduced parts inventory

Figure 9 illustrates the “One Piece” design approach. Note that structural steel spanning between the “B” pillars can be encapsulated into the polyurethane composite to maintain or increase roll-over integrity. Detailed cross-sections showing the sides of the module and attachment to the door were developed. Four distinct “One Piece” design concepts were developed for the “Over-the-Top” system architecture to represent various performance and economic solutions. The concepts were named: Traditional Look, Fixed Glazing, Robust/Metal Module Design, and Robust/ST Foam Roof Frame. Additionally, three distinct “One Piece” design concepts were developed for the “Recessed” system

Page 7

architecture to represent various performance and economic solutions. These concepts were named Integral-Wire-Way.

Substrate (SRIM) is moldeddirectly behind the paint film and the

headliner cloth-OR-

A traditional headliner system can bepost applied to the SRIM

Headliner

structural steel can be encapsulated (spanning between the “B” pillars)

to maintain or increase roll-over integrity

Paint film

Bayer Concept

Bayer Concept

Figure 9: “One Piece” Design Approach (Bayer MaterialScience)

Figure 10 is an example of the “One Piece” design concept for the “Over-the-Top” system architecture that represents the “Traditional” Look.

Multi layer film using Bayfol TP231

Baydur STR (glass mat, LFI) or Baypreg sandwich substrate

(molded behind the film)

Typical headliner system using Baynat foam.

-or-Substrate molded directly behind headliner material

Door

Locator / dowel

Assume this box section extends from “A” to “C” pillar

PU Elastomer seal(molded onto substrate)

*Bayer Concept*Bayer Concept Figure 10: “One Piece” Design Concept, “Over-the-Top” System, “Traditional” Look

Page 8

Figure 11 is an example of the “One Piece” design concept for the “Recessed” system architecture that represents one Integral-Wire-Way solution. Details of the other solutions are contained in the presentation that accompanies this paper.

Daedalus Concept #9Recessed

Section A-A with wire way detail

Isometric view of wire ways

Molded-in pathwayfor wiring

Molded-insnap-fits

for module assemblyonto roof frame

Baypreg(molded behind paint film)**

Metal paintedBody color

*Bayer Concept*Bayer Concept** active development

Figure 11: “One Piece” Design Concept, “Recessed” System, Integral Wire Way

The second option offered for either system architecture is the “Clam-shell” Design. Advantages of this design include:

• Best suited for applications requiring a higher level of parts integration into the roof module • Exterior piece/part is molded directly behind a multi-layer paint film, saving pos painting • Interior piece/part is molded directly behind the headliner cloth, eliminating the headliner foam • Interior piece can have molded-in features such as air ducts, wiring tracks, sun shade recess,

sun roof motor supports, other hardware supports, etc. • Interior piece, if constructed of BMS Baypreg PUR composite with a paper honeycomb core,

since it’s not exposed to the elements • All hardware items are easily mounted on to the interior piece • Exterior piece is glued on to the interior piece, after hardware mounting, creating a very rigid

structure • Potential increase in vehicle rigidity & torsion • Potential increase in roll over resistance • Reduction of parts inventory

Figure 12 illustrates the “Clam-shell” design approach with outer and inner panels. Notice the detail of wire ways and heating, ventilating and air-conditioning (HVAC) duct work that are formed into the inner panels. Five distinct “Clam-shell” design concepts were developed for the “Over-the-Top” system architecture to represent various performance and economic solutions. The concepts were named: Traditional Look, Rivet Attachment, Integral HVAC Ducts, Moveable Glazing, and Head Impact

Page 9

Protection. Additionally, four distinct “Clam-shell” design concepts were developed for the “Recessed” system architecture to represent various performance and economic solutions. Three concepts were named Robust Module, Integral-Wire-Way, and the fourth was a “Special” design concept named Integral Airbag.

Wiring harness

Detail of wire ways & HVAC ductwork

HVAC covers

Thermoformedmulti-layer film using Bayfol TP231

Dome light coverMakrolon / PC

Interior piece:Baypreg or LFI substratemolded behind theheadliner cloth

Bayer Concept

Bayer ConceptExterior piece: Baydur STR (glass mat, LFI) substrate(molded behind the film)

Figure 12: “Clam-shell” Design Concept, Outer and Inner Panels

Figure 13 is an example of the “Clam-shell” design concept for the “Over-the-Top” system architecture that represents the Moveable Glazing solution. Here Makrolon PC is the material of choice for the movable sun roof and the sliding shade is made with polyurethane composite with a paper honeycomb core and wrapped in cloth.

Movable sun roof (Makrolon PC glazing)

Sliding sun shade of Baypreg-F Sandwich orBaydur STR (glass mat)

The interior piece eliminates the molded plastic structure used to support the

motors/guides/cables etc.

Guides

Typical edge seal

*Bayer Concept*Bayer Concept Figure 13: “Clam-shell” Design Concept, “Over-the-Top System, Move-able Glazing

Page 10

Figure 14 shows the “Special” design concept for the “Recessed” system architecture named Integral Airbag. This design concept features an airbag package encapsulated in to the roof module with medium density polyurethane (PU) foam. Details of the other solutions are contained in the presentation that accompanies this paper.

Airbag boxencapsulated

Baydur STR (glass mat, LFI) exterior piecemolded behind paint film

Medium density PU foamis molded behind/onto the exterior piece,encapsulating any components desired,

including the headliner material

Wiresencapsulated

*Bayer Concept*Bayer Concept Figure 14: “Special” Design Concept, “Recessed” System, Integral Airbag

Value Proposition

The basis for the value proposition is the design concept’s universality and versatility that enables module interchangeability. Each module has its own customized performance, content, and economics. The concept allows the automotive OEM maximum flexibility in product planning and manufacturing. The various design concepts discussed previously in this paper are placed on an X and Y graph in Figure 15. The X axis is the module content from low to high. The Y axis is module performance, again, from low to high. The module design named “one-piece traditional”, closest to the point of origin on the graph shows the least content and performance, with presumably the least cost. At the other end of the spectrum is the “special integral airbag” design that features the highest level of content and performance, with presumably the most cost. In between could be and endless array of combinations for the OEM to choose from. At the product planning stage the OEM chooses several roof modules with different levels of merchantable content. Later the vehicle buyer considers the roof options, makes a choice and the order is sent to the factory for a specific module to be assembled for this customer. In each case the roof module is delivered to the OEM sequentially and ready for assembly. The roof module could be assembled inside the main vehicle assembly operation in a feeder line owned by the OEM or “co-located” with a system integrator or other tier-one supplier. The roof modules could also be assembled in a separate facility within close proximity to the main OEM assembly operation for just-in-time (JIT) delivery.

Page 11

The value proposition also offers the opportunity to address vehicle safety. An average of 3,700 deaths and serious injuries occur annually in rollover accidents in which the victims are belted and the roof is crushed, according to the National Highway Traffic Safety Administration (NHTSA). No subset of rollover statistics is under greater scrutiny by NHTSA, which may propose tougher, new roof-strength standards to replace the current ones enacted in 1971 [3]. Appropriate modular roof designs could effectively address this issue with the customer ultimately deciding the cost/benefit solution right for them.

Figure 15 Value Proposition (Bayer MaterialScience)

The basic value proposition was coined in the new phrase “uni-versital” body-in-white (BIW) header. The concept enables module interchangeability; each module having customized performance, content, and economics. The uni-versital BIW header is illustrated in Figure 16.

CustomizedContent

CustomizedPerformance

Uni-versital

BIW Header

Bayer Concept

Bayer Concept

Features Benefits

((((

roll-overside intrusion

occupanthead impact (homogeneity)

Differentiation

Assembly

(((

lower specific gravity materialsreduced piece count

(((

((

piece count / inventoryintegration

material selection

((interchangeability of modules

(interior assembly thru roof

Safety

Weight

CostTierOEM

Figure 16 Uni-versital BIW Header Concept Features and Benefits (Bayer MaterialScience)

Page 12

Value Proposition – DaimlerChrysler Dodge Caravan Case Study

A case study was used to examine the value proposition in four areas: cost, weight, safety and assembly. The analysis was based on the comparison of an existing “beam/skin” construction to a “structural plate” construction made from PUR LFT. The scope was a comparison of the existing Dodge Caravan to the same vehicle fitted with a PUT LFI roof module. The attributes that were studied included:

• Performance, FEA simulations:

1. knee load 2. wind load 3. torsion stiffness 4. modal analysis

• Weight • Value

The FEA results and conclusions showed that in the knee load simulation, the PUR LFT roof was 82% stiffer than the steel roof. The analysis measured the deflection simulated by one knee at a 115 kg load at the temperatures of 23° C and 85° C. In the wind load simulation done at 100 mph at 23° C and 85° C, the deflection results were considered almost identical. The roof torsion loading was measured at 23° C and 85° C with results showing the PUR LFT roof was 40% stiffer than the steel roof. The modal analysis was done with the roof only from the beltline up, 1st mode. The analysis showed that further optimization was possible. The results and conclusions from the FEA simulations are shown in Figure 17.

7.4 mm85 ºCsteel roof

Modal Analysis(“roof only” from beltline up, 1st mode)

36.8 hz23 ºCsteel roof29.4 hz23 ºCBaydur/LFT roof

+29 / -3085 ºCBaydur/LFT roof+29 / - 3023 ºCBaydur/LFT roof+ 47 / - 5223 ºCsteel roof

Roof Torsion Loading(left / right (mm), see loads & restraints)

6.9 mm85 ºCBaydur/LFT roof, Makrolon glazing

0.73 mm23 ºCBaydur/LFT roof, Makrolon glazing0.18 mm23 ºCsteel roof

Wind Load Simulation(100 mph)

4.2 mm85 ºCBaydur/LFT roof3.9 mm23 ºCBaydur/LFT roof

21.9 mm23 ºCsteel roof

ResultTempKnee Load Simulation(1 knee @ 115 kg load)

exceeds yield, permanent dent

82% stiffer than steel roof

almost identical

40% stiffer than steel roof

rev1, further optimization possible

Figure 17 FEA Results and Conclusions (Bayer MaterialScience)

Page 13

A weight comparison showed the vehicle installed with the PUR LFT roof module is 5.6 kg lighter than the existing vehicle with the all-steel roof. Figure 18 summarizes the details of the weight comparison analysis.

existing all-steel roof (from beltline up, featureless) ......... 102.4 kgBaydur/LFT roof module (i.e. PC glazing, steel pillars & roof frame) … 96.8 kg

2 molded Baydur/LFT parts only …………………….… 12.5 kg4 Makrolon windows ……………………………………… 2.5 kgremaining steel structure, pillars, and roof frame ……. 81.8 kg4 tempered glass windows (reference only) .................. 3.6 kg

Materials’ Details:Baydur/LFT composite includes 45% glass @ 75 pcf molded densityall surfaces are 3.0 mm thickMakrolon windows are 5 mm thick (could be optimized to be thinner)existing roof sheet metal is 1.55 mm thickexisting steel cross-car beams are 0.77 mm thick

vehicle installed with Baydur/LFT roof module is 5.6 kg lighterthan existing vehicle with all-steel roof

Figure 18 Weight Comparisons (Bayer MaterialScience)

The case study summary and conclusions showed that the PUR LFT structural plate compared to the existing construction resulted in:

• At lower weight and higher performance, the PUR LFT solution enabled more features and value

• At equal feature count and value, the PUR LFT solution offered lower weight and higher performance

• The PUR LFT solution enables “structural plate” constructions and more design freedom compared to the beam/skin designs.

Page 14

Figure 19 shows details of the case study summary and conclusions of the PUR LFT structural plate compared to the existing construction.

≤?n/a≥?System Cost

=>>=Cross-Model Value

=>>=Feature Value of Roof

≥≥>Performance

<<<<Weight

case study

1

2

3Existing Roofnot in case study

Steel w/ Windows

Baydur/LFT Roofper case study

PUR w/ Windows

Existing Roofper case study

Steel w/o Windows

Baydur/LFT Roofnot in case study

PUR w/o Windows

Summary Baydur/LFT vs. Existing

1 2 3

Baydur/LFT enables “structural plate” constructions and more design freedom vs. beam/skin designs.

At equal feature count & value, Baydur/LFT offers lower weight & higher performance.

At lower weight & higher performance, Baydur/LFT enables more features & value.Conclusions

Figure 19 Case Study Summary & Conclusions (Bayer MaterialScience)

An analysis of the case study comparing the existing Dodge Caravan roof to a PUR LFT design resulted in these key conclusions:

• PUR LFT enables a “structural plate” construction and improved design freedom compared to the metal beam/skin construction

• The PUR LFT “structural plate” design is over 25% stiffer in torsion rigidity that the existing metal beam/skin design

• The PUR LFT roof module is 5.6 kg lighter than the existing beam/skin construction of the Dodge Caravan

• At lower weight and higher performance, the PUR LFT roof solution enables more features and value

Page 15

Sample Application – Opel Zafira

The General Motors Opel Zafira roof is in production with a modular design. The structural carrier is made by Webasto with the PUR-LFT process. A black PC film is placed over the substrate material to deliver a Class A exterior appearance. Figure 20 shows the current construction.

Coextruded FilmCoextruded Film

Plan View

Interior View

PUR Baydur LFI Structural CarrierPUR Baydur LFI Structural Carrier

Courtesy of Webasto

Opel Zafira RoofCurrent Construction

Figure 20 Opel Zafira Roof – Current Construction

Page 16

Figure 21 illustrates an Opel Zafira roof concept based on a “Clam-shell” design. This concept features injection molded PC glazing and uses a PC and PC/ABS co-extruded film laminated with paint film to deliver a variety of custom colors to match the vehicle body. On the interior is a high level of integration featuring storage compartments and lighting.

Exterior piece:Baydur (glass mat, LFI) substrate molded behind paint film

Wiring harness

Interior piece:Baypreg Sandwich or Baydur (glass mat, LFI) substrate molded behind headliner cloth

Headliner cloth

Overhead storage compartmentsBayflex 110-80

Dome light coverMakrolon / PC

Makrolon / PC glazingFantasia colors

Multi-layer film using Bayfol TP231

Bayer ConceptBayer Concept

Figure 21 Opel Zafira Roof – Bayer Roof Solution Adaptation

Conclusions

The Opel Zafira is an example of a vehicle with a “non-traditional” roof system in production today. The carrier is made with a PUR LFT composite with PC film delivering black high gloss exterior appearance and performance. Paint film developments show the promise to open the pallet to a variety of custom colors with good adhesion and appearance on the PUR LFT composite. Future vehicles currently in the concept design and engineering phase incorporate PC glazing for panoramic roofs. These vehicles will feature advanced styling, integration and modular assembly. Fresh design and material concepts developed by Bayer MaterialScience show different vehicle architectures that enable component integration, post painting elimination, increased vehicle rigidity, and weight reduction. The value proposition’s “uni-versital” BIW header concept enables module interchangeability and allows the OEM to select a variety of customized roof modules with different levels of performance, content, and economics for a vehicle. Careful selection of merchantable content with assembly flexibility will provide an economic incentive to the OEM.

Page 17

Case study analysis demonstrated a PUR LFT based roof module system when compared to an existing vehicle roof offers:

• A “structural plate” construction with greater design freedom compared to the metal beam/skin construction

• The “structural plate” design is over 25% stiffer in torsion rigidity that the existing metal beam/skin design

• The roof module is 5.6 kg lighter that the existing metal beam/skin construction • More features and value can be offered at lower weight and higher performance

Bibliography

[1] C. Korson and D. Stratton, An Integrated Automotive Roof Module Concept: Plastic-Metal Hybrid and Polyurethane Composite Technology, Society of Plastics Engineers Automotive Composites Conference, September 2005. [2] A. Leroy and L. Schelisch, Dachmodul – am Beispiel des neuen Opel Zafira, VDI Society of Plastics Technology Plastics in Automotive Engineering Conference, pp. 161-179, March 2005. [3] W. Vlasic and J. Plungis, Seat Belts Not Enough to Save Lives in Rollovers, Detroit News: Special Report, April 2004.