Saving up to 100 kg in weight is a complex task, especially in the compact class. The fact is that not every carmaker is pursuing the route of lightweight design – searching for every last gram – as methodically or thoroughly as Volkswagen. The reason is clear: intensive research and development work costs money. And yet, the base price of the seventh generation Golf, which has not gone up by a single cent despite its higher specification, is a reflection of the innovative power of this brand
Overall vehicle – how savings add up to 100 kg
If you partition the Golf up into the primary areas of electrical, engines, running gear and superstructure, an analysis yields - depending on model, specification and type of engine - the following split for the weight reduction:
Up to -6.0 kg - Electrical
Up to -40.0 kg - Engines
Up to -26.0 kg - Running gear
Up to -37.0 kg - Superstructure
In purely mathematical terms the total potential saving is thus even as much as 109 kilograms. Due, however, to the configuration options that can be implemented in practice, the maximum achieved in any one vehicle is 100 kg. The greatest weight reduction is achieved from the engines and superstructure. It is particularly interesting to look into the details of the superstructure (car body and interior) and the 37 kilograms saved here, as it shows how lightweight design that is compatible with large-scale production can be achieved in 2012.
Superstructure – how savings add up to 37 kg
-0.4 kg - Dashboard
-1.4 kg - Module cross-member (beneath dashboard)
-2.7 kg - Air conditioning
-7.0 kg - Front and rear seats (depending on version)
-23.0 kg - Body
-2.5 kg - Miscellaneous.
Dashboard. 0.4 kg does not sound like much. But this is where perfection in the details comes into play. If 0.4 kg is overlooked, then ultimately a 100 kg will never be attained. Volkswagen not only succeeded in making the dashboard 20 per cent lighter thanks to a new thermoplastic foam injection process – the load-bearing, sandwich-like structure beneath the elegant surface consists of this material – but also in making it 20 per cent more rigid at the same time.
Module cross-member. The 1.4 kg saved here also contributes towards overcoming the upward weight spiral. Mounted on the module cross-member are both the steering gear and the dashboard. Altogether the cross-member weighs 5.8 kg. The reduction in weight was achieved with a lightweight design approach utilising steel components. Based on an analysis by Finite Element Method (FEM) computations, the structure of the module cross-member was designed to be as light as possible and as strong as necessary. Optimal steel wall thicknesses and structural design measures, such as specially worked-in corrugations, improved the rigidity of the cross-member, while also reducing its weight by the noted 1.4 kg. Utilising methods such as the Finite Element Method, engineers at Volkswagen are essentially emulating examples found in nature, where the natural world is able to attain an astonishing ratio between the cross-section of a part's structure and its rigidity – e.g. in a stalk of grass or grain. That is the right way to go.
Air conditioning. The Golf's entire air conditioning system has been redesigned and, as noted, is 2.7 kg lighter. Independent of its weight, all of the Golf air conditioning units with their highly efficient refrigerant cycles set standards in terms of comfort and efficiency. That is because they run very quietly (up to 5 dB(A) lower), they reach the desired temperature significantly faster and are very energy-efficient (up to 4 Amperes less) due to a new type of blower control with intelligent climate control. The 2.7 kg weight reduction is achieved by such design modifications as optimised wall thicknesses of various system components, reduced diameters of pressure lines, a new fastening system and a weight-optimised high-performance heat exchanger
Seating system. Along with numerous minor modifications to the seats, weight was reduced in other areas especially in the rear backrests to save a total of up to 7 kg. Once again, the Finite Element Method (FEM) and high-strength steels combined with laser welding made it possible to optimise wall thicknesses and profile geometries. Engineers achieved weight savings of over 15 per cent in this way and by using lighter backrest latch mechanisms.
Body. The body must be strong to guarantee optimal safety and maximum comfort. Nonetheless, its structure should remain athletically lean, so that the overall vehicle is light and efficient. Strong yet lightweight – harmonising these two parameters continues to be one of the greatest challenges in the automotive world. Especially when a car – like the Golf – needs to be an affordable car for millions of people. Highly expensive materials like aluminium, magnesium or even carbon-fibre are therefore excluded in this segment – at least when they are used in grand style. That is why Volkswagen relies on the synergies of the Modular Transverse Matrix (MQB), innovative utilisation of high-strength steels and advanced production methods. The success of this approach is demonstrated by realisation of a 23 kg reduction in weight in the car body structure - without additional costs while satisfying more stringent crash and rigidity requirements and implementing larger vehicle dimensions.
Body-in-white – how savings add up to 23 kg
-12 kg – Use of high-strength and advanced high-strength steel grades and reduction of sheet metal thickness
-4 kg – Only using materials where they are needed
-7 kg – Optimising profile and surface geometries.
High-strength and advanced high-strength steel grades. The share of high-strength steels has grown from 66 per cent to 80 per cent compared to the Golf Mk6. The decisive advantage lies in the fact that Volkswagen has built up extensive know-how in the development and production of ultra-high-strength, hot-formed parts since the Golf Mk6 and has invested in manufacturing facilities – more than any other carmaker in the world. The share of these parts that are up to six times as strong as conventional steel parts has grown from six per cent in the Golf Mk6 to 28 per cent in the new Golf. Moreover, new advanced high-strength steels are available on the market today that did not exist when the previous model was being developed. These represent another nine per cent in the new Golf. The advantage of these extremely strong steels: the finished parts made of them can be designed to be considerably thinner than before and still handle the stresses of a crash. Nearly the entire safety architecture of the new Golf consists of these steels, which effectively form the vehicle's backbone. And yet hot-forming also saves a total of 12 kg in weight.
Only using material where it is needed. The second lightweight design strategy – to only use material where it is needed – is an obvious one. Yet, it has been perfected in the new Golf. This effort even goes so far as to precisely vary the sheet metal thicknesses within a part; this is done at the rolling mill of the steel supplier, which delivers a tailor rolled blank (a rolled blank with variable thickness) to the hot-forming facility. One advantage compared to conventional tailored blanks is that eleven zones can be produced within a cross-member, each with optimal sheet thickness. The transitions between the different sheet thicknesses are uniform here and do not exhibit any abrupt changes in strength. The savings for just these parts: -4 kg.
Optimising geometries. Geometries of the load-bearing structure and surface parts have been optimised for many years. Continually improved virtual methods in the development process can be used to utilise existing installation spaces even more effectively. Take the example of the longitudinal frame member. Optimal utilisation of the mounting space between the engine and the front of the chassis enabled a 25 per cent increase in profile cross-section, which in turn enabled the use of thinner stock. Nonetheless, the entire front structure of the new Golf can absorb more energy in a frontal crash – thanks to geometry that is computationally optimised by FEM. In the case of surface parts such as the bulkhead and the floor, computationally optimised, acoustically effective corrugation patterns were introduced that also make the sheet metal more rigid and in turn lead to a reduction in sound insulating measures. Just these mentioned examples result in a weight reduction of seven kg.
New production methods. Welding processes and innovative tools also make a decisive contribution towards attaining high quality in body manufacturing. They are used to join and assemble all components – including the hot-formed steels and tailor rolled blanks. Some of them are making their debut in the new Golf. They include the laser clamp welder. This tool enables what are referred to as wobble welds, which are able to produce the joint between parts on a short flange. The ‘wobble' describes the sinusoidal path of the laser weld seam.
Hot forming. Hot-formed parts have an extremely high tensile yield strength of 1,000 MPa (Megapascal), which is over six times the strength of conventional deep-drawn steels and up to four times the strength of conventional high-strength steels. In the hot-forming process, a red-hot blank, heated to approximately 950 degrees Celsius, is inserted in the forming tool, formed in a work process and then quickly cooled in the tool. Excellent material properties are realised here.
Quieter and more comfortable
Acoustics perfected. In professional circles, the sixth generation Golf was already considered the quietest car in the compact class. Volkswagen set out to solidify this position with the new Golf. Therefore, innovative simulation tools were employed in the development of the seventh generation Golf; these tools were used to very precisely evaluate conceptual and component layouts with regard to their comfort and acoustics early on. This type of evaluation analyses parameters such as vibrations and sound pressure, which are perceived directly by the driver and passengers in the car. As a result, it was possible to transfer the high level of acoustic comfort of the previous model to the new Golf, despite substantial weight savings.
Example of running gear: The screw fastening concept for the front suspension was simplified, while the joining points were optimised for the modular performance suspension that is used for all Golf cars from 90 kW. This makes it possible to attain the greatest effect for acoustic ride comfort compared to the usual stiffening measures that are taken. The structure in the vicinity of the chassis leg connection to the occupant cell and the entire area around the strut towers were designed to minimise acoustic noise transmission to the interior. Specifically, engineers achieved a 5 dB reduction in ride noise compared to the previous model here.
Along with minimising the noise caused by unevenness of the road surface and running gear compensation for this, the development group also focused on eliminating engine noises as much as possible. In particular, the transmission of engine noise was reduced to an excellent low level in the conceptual design of the front subframe, as well as the zones around the strut towers, windscreen and firewall.
Engine mounts. A considerable share of optimal ride and vibration comfort is based on the method used for engine mounting. The mount elements were completely redesigned, while retaining the pivot bearing concept. Despite reductions in component weights, performance of the engine mounting system was improved. Along with reducing the amount of structure-borne noise (from the engine), important improvements were made in vibration damping; they were achieved by optimising the geometries of the engine and gearbox bearings. The new engine mount system for the Golf results in smaller movements of the engine assembly; and that is precisely what optimises ride comfort.
Quieter engines. As already noted, the new Golf is also launching with a new lineup of petrol and diesel engines. In these engines, acoustic needs were already addressed in the early development phase. Consider the TDI: by considering requirements early in its development, specific engine-related acoustic measures were implemented in the package to reduce the air-borne noise emissions directly at the source. This also included measures for optimal acoustic integration of the oxidation catalytic converter, the charge air tube, oil sump and dampers on the crankcase on the firewall side. In addition, encapsulating the engine compartment in a sound-absorbent material ensures conditions remain quiet both inside and around the Golf.
Wind, environmental and background noise. Thanks to the good aerodynamics of the new Golf, wind noises are effectively reduced; meanwhile, environmental noises are absorbed for the most part by the elaborately sealed body. However, comprehensive noise insulation of the engine and chassis involved the risk that background sounds – e.g. from the blower, actuator motors, toothed belts or the turbocharger – might be perceived, while they were masked by engine noise in the previous model. This problem was solved as well: intensive detailed work reduced or eliminated background noises right at their sources. This largely avoided the need for additional, secondary acoustic measures in these areas.
Acoustic windscreen. Just as in the sixth generation Golf, an acoustically effective damping film is used in the windscreen of the new Volkswagen as well. This film especially reduces noise or sound waves in the frequency range from 2.5 to 3.5 kHz. In addition, the use of absorbers in the front doors and innovative design of the door seals has achieved a further reduction in the amount of environmental noise that finds its way into the interior. The complete package of all acoustic measures has made the new Golf one of the quietest cars in its class.
Notes:
TDI, TSI, DSG and Twincharger are registered trademarks of Volkswagen AG or other companies of the Volkswagen Group in Germany and other countries.
Features and technical data apply to models offered in Germany. They may differ in other countries. All fuel consumption and CO2 emissions data cited in this press kit refer to official vehicle registration values (combined values), which were determined under standard conditions in the NEDC cycle. Fuel consumption and CO2 emissions values for the Golf 1.4 TSI with ACT (103 kW / 140 PS) and the Golf BlueMotion 1.6 TDI (81 kW / 110 PS) are forecast values as of September 2012.