Developing a vehicle is a hugely expensive exercise and, without new models, manufacturers find themselves with a diminishing market share – as recently demonstrated so well by MG Rover. It is not surprising, therefore, that automotive manufacturers with multiple brands utilise common vehicle platforms in order to maintain development costs at a manageable level.
Taking one set of basic components and building variants is nothing new. The early motor industry was dominated by chassis manufacturers and independent coachbuilders that designed and constructed bodies to order, enabling customers to purchase very different vehicles, albeit with the same underpinnings. MG went a step further, taking Morris chassis and modifying them before tuning the engines and fitting lightweight bodies that resulted in highly competitive sportscars rather than the sedate saloons for which the chassis had originally been designed.
By the 1960s, monocoque construction made the production of alternative bodies a more complex process. So instead, companies such as BMC adopted what became known as ‘badge engineering’, with perhaps the best example being the 1100/1300 series cars. Owing a great deal to the popular but small Mini, the Issigonis-designed Morris 1100 was launched in 1962. This was soon followed by the MG 1100, Austin 1100, Vanden Plas Princess, Wolseley 1100 and Riley Kestrel. The main differences between these models related to the frontal styling and the interior trim.
A similar-looking range of 1300 models was introduced later, an estate car (Traveller) variant was also produced, and BMC’s operation in Australia developed the 1500 Nomad that was essentially a hatchback version with a larger engine. Other global developments included
a glass-fibre bodied MG 1300 built in Chile,
a mildly restyled Innocenti Morris and Austin,
a Michelotti-designed three-box Austin Apache based on the 1100 and built in South Africa, and a restyled 1300 version of this latter vehicle built in Spain by Authi and sold as the Austin Victoria.
Today the concept of a vehicle platform is somewhat more complex, incorporating a variety of systems shared between vehicles but with styling that disguises the parentage. In fact not even the floorpan is common across a platform, as significant alterations are usually required to suit the individual models. However, the subframes, powertrain, suspension, steering, braking, safety and electrical systems are often common, as is the HVAC (heating, ventilation and air conditioning), but detail variations can be considerable. In terms of the resultant vehicles, the manufacturers can instil vastly different characteristics, as in the Volvo S40/V50, Mazda3 and the European Ford Focus and Ford C-Max, all of which benefit from the acclaimed global C1 platform (Fig. 1). Indeed, it has been reported that this platform is so successful that a stretched version of it could be used for the next generation of Volvo S60 and V70, Land Rover Freelander, Ford Mondeo, Ford Galaxy and possibly even the replacement for the Jaguar X-Type. This is despite the fact that 0.8billion ($1billion) is said to have been spent already in developing the CD6 Mazda6 platform for this role.
Meanwhile, at the smaller end of the automobile market, the recently launched Toyota Aygo, Peugeot 107 and Citroen C1 are more obviously all built on the same platform, whereas it is not so apparent that the Opel/Vauxhall Corsa, Astra and Vectra are all part of a common platform strategy.
But for the Opel/Vauxhall Meriva, a slightly different approach was adopted, with the emphasis being on common parts rather than common platforms. Beyond the engine, transmission and braking system, few major parts are shared with the other models. Nevertheless, numerous components and assemblies are developments of their counterparts on the other models, such as the front seats, air conditioning and the front and rear axles. For this project, GM requested its suppliers to take responsibility for more of the development, thereby avoiding high engineering resource overheads.
While this approach and the platform concept are feasible for large-scale production, niche market vehicles are harder to engineer at an acceptable cost; either an entirely new platform has to be developed or an existing mainstream platform has to be used – which often compromises the resultant vehicle’s performance and/or design. However, Lotus Engineering has come up with a new concept that is said to offer several advantages.
Versatile Vehicle Architecture
Revealed for the first time at the 75th Geneva International Motor Show earlier this year, the Versatile Vehicle Architecture (VVA) understructure is constructed almost entirely from aluminium subcomponents. The structure uses high-pressure die cast corner nodes that are key to an architecture that additionally draws upon Lotus’ extensive experience with bonding, extruded aluminium, composite body engineering and vehicle systems integration (Fig. 2). This innovative technology offers a fast-to-market, cost-effective approach to differentiated niche products by spreading the development, investment and bill-of-materials burden across a range of niche vehicle variants, without the compromises that stem from conventional ‘platform sharing’.
The philosophy is based on the commonality and versatility of key elements of the vehicle structure and body systems across a ‘family’ of variants, with a combined annual production rate of up to around 50 000 units. Structural components common to the family members are arranged in different configurations in each variant around the ingenious corner nodes.
It is claimed that the great advantage of this technology is that it can be used by one OEM looking to develop a range of niche products or, alternatively, by a group of OEMs looking to share investment while still retaining a high degree of end product differentiation.
Steve Swift, head of vehicle engineering at Lotus Engineering, comments: “We believe it is a technology that provides solutions to a wide range of manufacturers. The worldwide vehicle market continues to sub-segment at a rate greater than its overall growth, leading to lower volumes per vehicle variant. OEMs are looking for architectures that give them a superior investment return with a high degree of product separation. VVA gives them that opportunity.”
The VVA understructure is aluminium riv-bonded, with high-pressure die-castings, stampings and extrusions, and uses advanced assembly techniques such as adhesive bonding, self-piercing rivets and flow-drill screws. Self-piercing rivets are used in a similar way to spot welding on a conventional steel shell, with flow-drill screws used for single-sided access on closed sections. Both hold the structure together during the bonding cure cycle, as well as preventing adhesive the joints from peeling in the event of a crash.
Nevertheless, the heat-cured, high-strength structural adhesive is the main joining medium and, used in combination with mechanical fasteners, it produces strong, durable joints and, therefore, a lightweight shell with exceptional torsional stiffness.
Lotus Cars has already stated that it will use the VVA concept for a forthcoming range of sportscars. The understructure shown at the Geneva Motor Show exhibited the principles by which Lotus will engineer its own products. Steve Swift said at the time: “I’m very pleased to be able to demonstrate how far we’ve come with VVA. The understructure proves the concept and we’re excited about the possibilities the technology brings to OEMs worldwide. We expect that the demonstration of this technology through a real understructure will stimulate yet more interest from OEMs or consortiums looking to produce exciting products utilising cost-efficient, proven architecture.”
Lotus Engineering gives the following examples of VVA families that could be constructed, with annual production volumes in brackets.
- Family A: front-engine, four-wheel-drive crossover (15 000), mid-engine, rear-wheel-drive supercar (5000), front-engine, rear-wheel-drive coupé (10 000) and front-engine, rear-wheel-drive saloon (20 000).
- Family B: front-engine, front-wheel-drive coupé (10 000) and front-engine, four-wheel-drive SUV (25 000).
- Family C: mid-engine, rear-wheel-drive coupé (5000), front-engine, front-wheel-drive saloon (25 000) and front-engine, four-wheel-drive crossover (30 000).
With over 20 000 built, the Lotus Elise has proved to be the most popular Lotus ever produced, illustrating how the company’s philosophy of ‘performance through light weight’ is a cost-effective alternative to the muscle-car approach. A more extreme development of this car has also found favour among customers in the form of the Lotus Exige (Fig. 3).
Building on this success, Lotus Cars has now developed the Circuit Car, an all-new lightweight and high-performance model aimed at customers wanting a car for track days and club motorsport (Fig. 4). Like the Exige, it is based on the Elise aluminium chassis, but it only weighs around 600 kg. The single-seater car (with an option of two seats) has lightweight composite open-topped bodywork that also generates high downforce due to cleverly engineered aerodynamics. Part of the car’s phenomenal performance results from a supercharged VVTL-i (variable valve timing with lift – intelligent) engine that is expected to propel the car from zero to 160 km/h (100 mph)
in 9.0 seconds.
An entry-level naturally-aspirated VVTL-i engine will also be available, yet this unit will still be capable of powering the car from zero to 100 km/h (62 mph) in under 4 seconds.
Tony Shute, head of product development at Lotus Cars, explains what he believes will make the Lotus Circuit Car a leading high-performance track car: “The new product has allowed Lotus to once again apply its key ‘performance through lightweight’ philosophy. This is in order to achieve an innovative product for the track day and club racing Lotus enthusiast whilst staying true to the key design attributes of the Elise and Exige products. They are considered to be amongst the finest existing road and track day cars by thousands of owners around the world, and the Circuit Car will build on this formidable reputation, helping to further underline Lotus as the ultimate driver’s choice.”
The Lotus Circuit Car is due to go into production at the Group Lotus Headquarters in Hethel, Norfolk, in December 2005, with a scheduled volume of approximately 100 units per annum.
While such high-performance vehicles will, unfortunately, only be enjoyed by a lucky few, the benefits of the Versatile Vehicle Architecture concept could be something that many more owners will be able to experience in the near future. m