tHe new golf BODY

STRICTLY ENFORCED LIGHTWEIGHT DESIGN For the new Golf, body lightweight design is the key to reversing the spiral of increasing weight for the whole vehicle. At Volkswagen, it goes without saying that the Golf still fulfills the increasing demands in terms of safety, comfort, production quality, and customer advantages.

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AUTHORS

dr. mArKus KleimAnn

is Head of the Body Design Engineering Department at Volkswagen AG.

tomAs scHorn

is spokesperson for the Body Engineering Group at Volkswagen AG.

body structure

Increasing awareness of the finite nature of oil resources and the pressing discussion for a reduction in CO2 emissions gave an even greater meaning to the issue of lightweight design in the development of the new Golf. The result is the Golf with the modular transverse kit (MQB) as a basis, in a lightweight steel design with significant weight savings of 23 kg in the body structure as well as reductions in material costs and production time. This means: Lightweight design without additional costs. mQb

The MQB is a cross-class concept, which means that variability in the wheelbase is governed by the length of the floor panels. In this process, one tool is able to produce the five floor panels of different lengths. Width variability is ensured solely by the inner sill and the strut tower. In this way, vehicles from different vehicle classes (Golf, Passat, etc.) can be covered. The basic structure of the rear end is designed such that the same side members and cross-members can be used for November 2012

The New Golf

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The New Golf BODY

❶ Left: Different gearbox connections for the PQ35 versus the MQB, right: Profile section for the side member comparison in front, PQ35 versus MQB

all three axle variants – torsion beam suspensions, multi-link suspensions with front-wheel-drive, and multi-link suspensions with 4MOTION. Because all powertrains of the MQB have the same installation position, also the main bearing structures in the front end are all identical. This is a tremendous advantage for vehicle manufacturing in factories worldwide. Due to ever-increasing requirements for the front side members as a result of overhang shortening and occupant load criterion (OLC) reduction, the height of the side members has been increased by 25 % and the cross-section has been significantly harmonized in comparison to its predecessor, ❶. The partition plate, as the drive train element of the bumper system into the front side member structure, is spot-welded in the MQB tolerance-free after the body structure is finished. Today, the side members are designed in the front area as a C-profile and include an end plate of the same grade. By embed-

❷ Closed torsion ring around the bulkhead in the MQB

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ding the transmission mount in the side member, we have been able to increase local stiffness and still reduce weight. The transition area from the side member to the area below the front floor is made of press-quenched steel. The extended heel crossmember features two-staged thickness, designed as a tailored blank component. The whole front end, but in particular the components around the bulkhead, have been optimized in terms of global and local dynamic stiffness. An allaround, self-contained torsion ring provides global basic stiffness, ❷. Arrangement of components

The side member forces in the transition area from the front end to the passenger compartment are distributed by the profileforming upper and lower footwell crossmember. The likewise press-quenched, one-piece tunnel is responsible for force distribution in the vehicle center; towards

the outside, the press-quenched inner sills fulfill this function. At the transition from the front to the rear floor assembly, the hot-worked heel part assumes the loaddistributing function for a side crash. The customized sheet thickness distribution by tailor-rolled blank technology facilitates deformation zones at the proper positions and leads to weight reduction. This alone amounts to 2 kg in comparison to a component with a uniform wall thickness. In order to fulfill all requirements, also the crossmember below the trunk floor panel between both wheel housings is hot-worked in one piece. The seat position is comparably lower than in the Golf 6. We were able to save 1.2 kg as compared to multi-piece, cold-worked variants. The press-quenched side members form the closing end to the rear. In order to permit deformations only in the rear part of the side member in the event of a rear crash, it is only partially hardened – that is, the rear part remains unhardened. The sheet thickness of the trunk floor panel has been reduced, while simultaneously achieving an increase in quality. Through the targeted swaging of the spare wheel well, it was possible to omit the star bracket of the predecessor while increasing volume by 8 l. Hat

A consistent lightweight design was also used for the hat. The A-pillar, with the inner and outer profile of the upper roof frame, together with the hot-worked inner sill, forms the lateral frame made of pressquenched steels. The system is terminated by reinforcement of the B-pillar, which is manufactured from a hot-worked tailorrolled blank in the new Golf, ❸. In doing so, the thinner upper and lower areas are connected by a thicker transition area in the center. They are nested on the blank in such a way that a material utilization ratio of over 70 % is achieved. A “laser collet chuck” is used for the first time to join the sheet metal parts. This means that so-called “wobble seams” are possible, ensuring the component joining on short flanges. These wobble seams are located in the front quarter glass as well as on the side panel and on the base of the B-pillar reinforcement, ❹. In the pro­ cess, sinusoidal laser welding connections are produced. These connections are able

❸ The sheet thickness distribution of the hot-worked B-pillar reinforcement of the Golf 7, manufactured in the tailor-rolled blank process

to withstand stresses many times more than individual weld spots, but can be manufactured in the same amount of pro­­ cess time. The complete door X-flange is laser-welded – as it was already done so in the predecessor model. The sheet thicknesses of the largest hat components – the side panel and the roof – have been reduced once again. This means a weight advantage of several kilograms in the blanks. Because of low material thicknesses, this also represents at the same time a large challenge for the Press Shop and Car Body Manufacture areas of the production plants. Component handling and laser soldering of these components is significantly more difficult, but has been resolved through efficient teamwork. The lower window frame of the windshield also presented a big challenge. On one hand, it has to ensure a stiff connection for the windshield. On the other hand, it has to be designed to be as resilient as possible for pedestrian protection. Our success due to the use of a crossmember in tailored blank technology with the resulting wall thicknesses distributed variously. The material quality distribution in the new November 2012

The New Golf

Golf demonstrates a marked increase in ultra-high-strength and hot-worked parts as compared to the predecessor model, ❺. Unlike its predecessor, 28 % of the components in the new Golf are made of pressquenched material. The front side members, seat cross-members as well as the outer sills consist of the highest strength grades (9 %). Moreover, the portion of high-strength steels remains almost

unchanged, as compared to the previous model. Soft deep-drawing steels only represent 20 % in the new Golf, unlike the 34 % in the Golf 6. By significantly increasing the material grades used, but in particular for the press-quenched components, it was possible to achieve weight savings of 23 kg, despite significantly more stringent requirements regarding performance and flexibility. The new Golf is therefore well-prepared for the future. This also applies to upcoming alternative drive train systems such as those used in electric drive or plug-in hybrid electric vehicles. In sum, the same weight of the body structure as in the Golf 4 has been achieved. This was based on the described use of high and ultra-high-strength steel grades, in particular hot-worked steels, and the reductions in sheet thicknesses this made possible – all this combined with tailor-rolled blank and tailored blank technologies, and a consistent use of optimization processes for profiles, nodes, and surfaces. With the add-on parts taken into the equation, the Golf 7 is even lighter than the Golf 4 with comparable engine types, despite increasing demands regarding comfort, safety, emissions, and equipment. For the new Golf, body lightweight design is the key to reversing the spiral of increasing weight for the whole vehicle. Lightweight design in the interior

The development of the cockpit carrier for the new Golf made use of a lightweight design strategy using steel components. Through the use of the finite element

❹ Left: Wave structure of the wobble seams, right: Base of the B-pillar reinforcement with wobble seams

The New Golf BODY

method (FEM) over the entire development process, it was possible to continuously optimize the cockpit carrier. As a result, wall thicknesses have been adjusted to real loads, among other things. Structural solutions such as bends and swages have been optimally positioned and di­­mensioned. The result is a weight reduction of 20 % with a simultaneous improve­ment in stiffness, ❻. Structure layout and stiffness

❺ The distribution of material quality, Golf 6 versus Golf 7

❻ Lightweight steel design in the cockpit carrier

❼ Rolling noise comparison at the driver’s ear

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Again, the focus of development for the Golf 7 aimed at building on its predecessor’s structural layout and maintaining a top spot in the competitive field in customer-relevant properties. This Golf will continue to set the standard within the class that bears its name. With detail optimizations of the body design, the foundations for various quality factors were laid. The spectrum extends from the best possible appeal through small gap dimensions all the way to structural durability in the presence of even the heaviest loads. With the modular strategy and the already outlined weight savings of 23 kg, the requirements for profile dimensions and the optimization of sheet metal areas gained center stage all the more. As an example, the local dynamic stiffness values of the suspension strut connections in the front end have been significantly increased by an optimal profile design in the bulkhead in the area of the plenum panel. Together with the design of the subframe connections, rolling noise has been reduced through targeted matching of stiffness values for structure-borne noise transfers from the force application points to the occupants, ➐. The noise-emitting surfaces in the area of the bulkhead have been provided with free swage forms as a result of numerical optimizations and with consideration of the available packaging space, ❽. The natural frequencies of the sheet metal areas were increased as a result, so that they are above the dominant excitation range of the engine. The foundations for a lower interior noise level are thus set on the body side. Excellent properties of the whole vehicle regarding comfort and vehicle dynamics already induce exceptional characteristic values for the body structure. 27,000 Nm/° made it possible to surpass the already very good values of the previous model in

static stiffness characterized by the bodywork. The dynamic stiffness values of the body structure increase to over 48 Hz for the natural torsional frequency and to over 50 Hz for the natural bending frequencies. This includes the dynamic properties of the equipped body for the subjective and objective criteria of drive comfort, particularly on uneven roadways. Furthermore, the natural torsional and bending frequencies of the “trimmed body” ensure excellent behavior for the new Golf with substantially greater 30 Hz. With the use of high and ultra-high-strength steel grades, the sheet thicknesses for components with loads relevant for stability could be reduced. Despite the reductions in sheet thickness, the stiffness effect associated with this has been more than compensated by profile-intensive lightweight design. Overall, the design of profiles has been optimized, combined with a use of materials matched to the respective load. Thus, the Golf is and remains the standard in the competitive environment, ❾.

rolled blank technology, as described in the previous section. In a side crash, this facilitates the purposeful design of deformation zones in an optimized footwell package. The press-quenched inner sill is supplemented by a rolled profile of ultrahigh-strength steel, upon which the reinforcement of the B-pillar is mounted. This is also designed in tailor-rolled blank technology. Along with weight reduction, this has the benefit of permitting a load-contingent adjustment to the bending moment occurring in the barrier load scenario. Thus, the necessary degree of flexibility is given to set the desired kinematics of the B-pillar. The same holds true for the geo-

metrical design that promotes deformation in the foot area of the B-pillar. This is also supported by the sill, designed to be flexible in terms of torsion. In addition to the B-pillar, also the roof frame on its interior and exterior is made of press-quenched steel. Because of the high strength of the material, the wall thicknesses were able to be reduced here as well. To connect highly resilient components with one another, wide areas are joined by laser welding. In highly-stressed zones, the shape of the lines has been diverted, following instead a wave-like shape that allows for a maximum joining area. In addition, adhesive bonding is increasingly

Crash safety

The platform of the new Golf, characterized by a frame structure made of pressquenched components, leads to a significantly stiffer platform structure, comparably. This manifests itself with an increase in survival space in the load scenarios for a front, side, and rear crash. In a front crash, the front side members, which are made of dual-phase steel, are particularly noteworthy, ❿. In the event of a crash, purposefully integrated swages allow this side member to buckle at defined points. With the emerging buckling modes of both side members, the crash energy is successively reduced so that a stable passenger compartment and thus a safe survival space is ensured at the end of the crash phase. The part of the side member that is diverted in a targeted manner under the floor assembly is made of pressquenched steel and transfers the incoming side member forces into the footwell crossmember. This is a crossbar located in front of the floor structure, and is also made of press-quenched steel. Deformation elements of the bumper system matched to the force level of the side member complete the deformation zone for a front crash. The heel plate has different wall thicknesses due to the tailorNovember 2012

The New Golf

❽ Bulkhead with free swage forms

❾ Comparison of body stiffness by competitors

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The New Golf BODY

❿ Front side member made of dual-phase steel

being used, which is suitable especially for press-quenched components since there is no entry of heat. Both rear side members are designed as partially quench­­­ed and tempered components with a defined transition zone. In this way, the side members meet the requirements for a rear crash. The unquenched and untempered section is located at the rear end of the side members and deforms in a specific way during a crash. In contrast, the press-quenched section is an extremely stiff structure and permits only slight deformations, whereby the survival space of the rear seat passengers is maintained. Newly designed panoramic tilt/slide sunroof

The objective defined the development of a roof system for the new Golf that provided extensive customer advantages and a large degree of inspiration at the same time. Therefore, high demands were placed on this roof system, including for example: :: enhancing the sense of inspiration :: creating a roof system for vehicles with smaller packaging dimensions

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:: providing a ventilation and opening function :: fortifying the “optical windshield extension” design trait :: designing the system as a top-load system. Beyond these requirements, the roof glass surface, the opening, and the visible light surface (molded headliner cutout) was expanded, as compared to the normal tilt/slide sunroof of the previous model. The molded headliner cutout (light opening), for example, was enlarged by 33 %, ⓫. According to a study by Professor Aldo Ferrara from the Medical University of Siena, Italy, roof opening systems contribute to general well-being. By improving the vehicle interior climate, they increase active safety. In addition to these climaterelated improvements, the light factor in the vehicle interior gains more and more importance. A light, spacious vehicle interior and the incorporation of the roof system into the exterior design increase the appeal of the whole vehicle. These in­­sights led to the development of this special roof system and to its use in the new Golf. An additional objective in the development of this roof system was the

reduction of installation costs. By means of a completely pre-assembled and tested roof system as a module (including sunshade system, glass cover, guide rails, mechanical elements, mounting frame, electric drive, and sealing system) and by implementing a top-load system, a significant reduction in production time has been achieved as compared to a traditional in­­stallation principle (for example, bottom-load system of a tilt/slide sunroof). The panoramic tilt/slide sunroof is first gathered by a manipulator in the production process and an adhesive bead is applied all-around. Then the module is aligned and fastened on the body flanges all-around by an adhesive joint. In addition, a new manual sunshade system is being used, an innovative further development among all current sunshade systems that improves occupant comfort, ⓬. The tinted, heat-insulating glass cover serves the same purpose, reflecting 99 % of UV radiation, 92 % of heat, and 90 % of light. Apart from the benefits in terms of the vehicle interior climate, room perception, and design integration, the new roof system of course also complies with legal requirements regarding an automatic reversal system.

Heated and heat-reflecting windshield – a global innovation in the Golf class as an option, the new Golf includes an all-season window, which is being offered for the first time in its class. The new windshield combines the advantages of wire heating with those of the laminated glass window into a “heated and heat-reflecting windshield”. This has been made possible through a sheer, electrically conductive coating, which can be heated in the window glass laminate. In the cold season, this window can prevent fog-up and be used as a defrosting aid, ⓭. In the warm season, it ensures only slight heating of the vehicle interior through the sheer coating reflecting a large portion of solar radiation. Along with an increase in thermal comfort, the environment is also less burdened, ⓮, since the air conditioning system does not have to provide as much power for cooling due to reduced heat. Vehicle fuel consumption also drops as a result. The new heated and heat-reflecting windshield thus makes its contribution toward a relaxed, environmentallyfriendly, and safe drive.

specially developed for this use ensures low release forces. At the same time, the required release path can be minimized because, due to the eccentric disk, the maximum speed-reducing ratio is only used when the highest force to unlock the swiveling system is required. Since the socket is already integrated in the ball neck, the trailer hitch of the new Golf is immediately ready for operation after swiveling out. It enables the customer to pull a trailer with a towing capacity up to 2 t and a trailer nose weight of 80 kg. With this strategy, Volkswagen is now offering the comfort of a swiveling trailer hitch at a favorable price in the compact class. Taillamp assemblies

The Golf’s newly designed taillamp assembly also carries the brand’s signa-

ture, introduced at Volkswagen with the w Polo, and which has been consistently implemented and further developed: The distinctive “L” design with the “eye” shows the rear position lamp and the brake light of the two-part bulb lamps with high precision and homogeneity at night. The sharpened contours of the styling bezel underline the brand identification image in a daytime design and dovetail seamlessly with the precision of the newly designed rear end of the vehicle, ⓯. A light-engineering challenge during development was the side panel lamp. Through maximal utilization of the avail­ able package for the reflector, an optimal result has been realized. Due to similar reflector depths – both in the side panel and also in the liftgate lamp – the intensities of both lamp parts are also very similar, even from lateral view angles. Below

Mechanically-swiveling trailer hitch

Customers can order the new Golf with a trailer hitch that features a swiveling ball neck. Particular attention has been directed toward the functionality of the release handle. This is integrated in an ergonomically beneficial and well-visible manner in the lock carrier cover. Even when the trunk is loaded, the handle can be accessed in an ideal way at any time. Since it is covered when the liftgate is closed, accidental misuse is ruled out. With the aid of a special torsion profile on the Bowden cable and an additional guide on the handle base, directed retraction and positioned storage of the release handle is ensured. This also fulfills the high requirements for the gap pattern in the ve­­ hicle interior. If the handle is pulled, the Bowden cable unlocks the swivel mechanism and the trailer hitch ball falls into the visible and easily accessible neutral position. If the system is in an unlocked status, the LED lamp next to the release handle flashes red as a security alert. In the locked operating or rest position, it is continuously green. The variable speedreducing gearbox with an eccentric disk November 2012

The New Golf

⓫ Panoramic tilt/slide sunroof (PASD)

⓬ PASD: installation position in the body

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Th e New Golf BODY

⓭ Visible resistance wires have been eliminated with the heated and heatreflecting windshield/windshield heater

DOI: 10.1365/s40111-012-0318-7

the rear position lamp and brake light function in the side panel lamp is the turn signal, which forms a visual unit with the two reversing lamps of the inner tailgate lamp. The reversing lamp feature has been integrated in both inner lamps, contrasting with the design of the Golf 6. By means of simulations, the available luminous flux has been optimally distributed. It provides the driver with adequate light in the pertinent areas. The rear fog lamp is located in the tailgate lamp next to the rear position lamp. As in all compact models of Volkswagen, it is designed as a one-sided function. The retro-reflector feature is positioned in the bumper and

⓯ Taillamp assembly

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⓮ With the heated and heat-reflecting windshield, only 40 % of solar radiation reaches the vehicle interior, in contrast to the usual 65 %

blends seamlessly into the overall rear design of the vehicle. Headlamps – greater selection

Within the range of the 7th generation Golf, the customer is able to choose among four different headlamp variants. In the basic version with an H7 (Longlife) low beam, the luminous flux was in­­ creased by more than 10 % as compared to the predecessor. The combination of high beam and separate daytime running lights, assembled in one reflector by means of one H15 lamp, well-known from the Golf 6, has been expanded by

⓰ Headlamps

the front position lamp feature. This triple functionality is achieved by dimming the separate daytime running lights coil via the electric system control unit. The result is a reflector appearance with clear structures, due to the fact that the formerly used, additionally required W5W lamp in the reflector, is no longer necessary, ⓰. For the first time at Volkswagen, three xenon variants of the headlamp are offered in the new Golf. They are equipped with mercury-free 35-W xenon gas-discharge lamps (D3S) and project light onto the street using a double-ellipsoid reflector and a plano-convex lens (bi-xenon module). The rigid xenon entry

variant offers a highly attractive customer price and provides the separate daytime running lights by means of a PW24W bulb. This same lamp also provides for the front position lamps via dimming. In addition, a static cornering light is integrated into the headlamp in a separate reflector, which dims down after the turn signal is set or when the vehicle turns at speeds of less than 40 km/h and illuminates the inner curve area, thus contributing to active driving safety. Compared to the previous model, in which this feature was arranged in the bumper in conjunction with the front fog lamp, a larger range and a higher luminous flux results due to the higher installation height and a design with a separate reflector. In the two top xenon variants, different light distributions are implemented depending on the driving situation, which are automatically activated. Along with the static corning light and the dynamic corning light, in which the light beam follows the curve shape, this feature also adapts to

specific circumstances during drives within and outside of city limits (city light or country light), as well as on freeways. In the highest equipment variant, continuous driving with the high beam outside of city limits is also possible through “Dynamic Light Assist” (DLA). With this feature, a camera behind the windshield detects vehicles in the front and relays their position to the headlamp electronic system. This controls a cylindrical beam shield in the xenon module, which masks the light segment that could blind the occupants of the ap­­proaching vehicle or the vehicle in front. This feature is available for the first time at Volkswagen in the Golf class. The separate daytime running lights in the top xenon variants are implemented in LED technology. If individual lights had already been used in the previous model, a uniformly luminous, threedimensional light body is now arranged around the xenon module. This is also used for the first time in a Golf. As the light source for this so-called “thick-

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walled optics”, 18 LEDs are used with 0.5 W power consumption each, which are arranged transversely to the direction of travel and use reflectors to feed their light into the optics. The complex thickwalled optics are made from PC (polycarbonate) in a 2-cycle injection-molding process. This process prevents the formation of sink marks on the surface that would otherwise occur in a single-cycle injection process. Due to the layout of the reflectors and the surface structure, also the lateral surfaces of the optics are illuminated so that a three-dimensional light body is formed. Not only does this increase the visibility of the separate daytime running lights from the side, but the light body also lends spatial depth and distinctive light graphics to the headlamp. After switching on the low beam, the LEDs are dimmed to the level of the front position lamps. In addition, a “light finger” is activated, which distinguishes the appearance at night from that during the day.

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Richtig schalten. November 2012

The New Golf

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