The Aluminium Performance Crossover - APX

APX is a 7-seater (in reality a 5 + 2 with the two rear seats being occasional) four-wheel drive -Crossover' vehicle with a front mounted 300 hp supercharged V6 petrol engine. Weighing in at just 1570 kg and with a power to weight ratio of 191 hp per tonne, the APX has sportscar like performance of 5.4 seconds to 100 km/h (5.0 seconds to 60 mph) before reaching a top speed of 245 km/h (152 mph). These performance figures are as good as the highest performing 4x4 -Crossover' vehicles from other brands with up to 195 hp per tonne. Crucially though, whereas those vehicles need higher output engines to compensate for heavy weight, APX does not. Combined fuel consumption for APX is estimated to be 8.7 litres / 100 km (or 32 mpg) - impressive on its own and more so when compared to its production rivals which often consume more than 13 litres per 100 km (22 mpg).

APX is manufactured predominantly from aluminium in the form of high-pressure die-cast corner nodes, stampings and extrusions. It uses advanced assembly techniques, including adhesive bonding, self-piercing rivets and flow-drill screws for construction - joining techniques that Lotus calls Riv-Bonding. Lotus has optimised the use of these technologies thus significantly reducing the number of mechanical fixings within the monocoque structure. This has reduced the level of investment required in manufacturing equipment.

APX is not just a Lotus Engineering concept, but a feasible prototype close to production.It is a brilliant demonstration of VVA and the skills of the team from Lotus Engineering. It is production feasible as all the components can be made cost effectively and in high niche volume (up to around 30,000 per year).

APX is powered by a V6 engine has been designed by Lotus Engineering. The engine is a supercharged 3 litre (2996 cc, Bore: 88 mm, stroke: 82.1 mm) V6 DOHC engine, mounted longitudinally in the front of the vehicle.Performance of the engine is maximum power of 224 kW (300 hp, 304 PS) at 6250 rpm and a torque of 360 Nm at 4500 rpm.

The key to the VVA architecture is the high-pressure die cast corner nodes that are combined with bonding, mechanical fasteners, extruded and pressed aluminium. Lotus Engineering is a world leader in aluminium, steel and composite body engineering, joining techniques, and vehicle systems integration. The innovative VVA 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 compromise that stems 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 niche vehicle variants, with a combined annual production rate of up to around 50,000 units. Structural components common to each family member are arranged in different configurations in each variant around the ingenious corner nodes.

Traditionally OEMs seeking to gain competitive advantage through exciting niche vehicles have to either design a new platform or share one already available. Engineering a bespoke low-volume platform is an expensive, time-consuming solution, whilst sharing a mainstream chassis normally results in compromises in performance and design.

Exciting products are needed to allow vehicle manufacturers the freedom to differentiate. Lotus Versatile Vehicle Architecture (VVA) was conceived to allow versatility across a variety of product types. This enables you to exploit the benefits of producing niches vehicles at medium volumes, profitably.

Lotus Versatile Vehicle Architecture (VVA) has been developed to bridge a gap in the investment-volume curve to exploit the benefits of producing at medium volumes but for niche markets, thereby giving the best chance of business case success and favourable returns. The great advantage of this technology is that it can be used by one OEM looking to develop a range of niche products, or by a group of OEMs looking to share investment, but still retain a high degree of end product separation.

Aluminium was selected for the VVA for the following reasons:

• Light weight typical 40% mass saving over steel for body structures
• High specific strength of certain grades
• Technology image
• Utilise processes infeasible for traditional materials i.e. thin wall Al castings and extrusions.

Why Extrusions?

• Reduce tooling investment
• Improve part integration
• High strength compared with sheet material for crash applications
• Reduce lead and optimisation times
• No joints to unstitch - improved collapse mode
• Weight reduction (optimised profile gauges & removal of flanges)

Aluminium vacuum high pressure die castings have been adopted throughout the vehicle structure to meet the following criteria:

• Improved part integration - achieve complex form only feasible as complex assemblies
• Improved dimensional tolerances and repeatability
• Increased BIW stiffness targets
• Local suspension point stiffness
• BIW torsional and bending stiffness
• Tailor and minimise gauge, material added where required

Joining Technologies

• Self pierce rivets used in combination with heat cured single component epoxy adhesive
• Compared with other similar joining methods the Lotus route places more reliability on the adhesive for structural performance, therefore reducing the number of rivets required with associated lower capital equipment investment
• Adhesive is robotically applied for production and cured during the ecoat process. Ejot fastners used where single sided access is infeasible

The V6 engine in the APX is an example of extensive research into -engine downsizing' by Lotus Engineering . Engine downsizing is the concept of using advanced technologies to enable a small engine to produce the power and torque of a much larger engine, with the obvious reduction in fuel consumption and emissions.

The directive for the project was to produce a high performance prototype engine without the need for exotic materials or manufacturing technology, allowing manufacture around the world.

The production-feasible supercharged V6 is part of a family of normally aspirated and supercharged high performance engines which includes 2.2 litre and 3.0 litre derivatives.

APX's engine is a supercharged 3 litre (2996 cc, Bore: 88 mm, stroke: 82.1 mm) V6 DOHC engine, mounted longitudinally in the front of the vehicle. It uses a Rootes-type supercharger with a compact air-to-water Laminova-type charge cooler with separate parallel coolant system using its own water pump and heat exchangers.

Performance of the engine is maximum power of 224 kW (300 hp, 304 PS) at 6250 rpm and a torque of 360 Nm at 4500 rpm. 80% of peak torque is between 1500 rpm and maximum revs of 6500 rpm.

Like all products from Lotus, it follows the adage of -performance through light weight', in that the engine weighs just 171 kg (fully dressed, dry weight). This gives a phenomenal specific output of around 1.31 kW/kg (1.7 hp/kg). Specific performance is 74.6 kW / litre (100 hp / litre, 101.3 PS / litre).

The light weight comes from using cast aluminium alloy cylinder block (with thin wall iron liners), an aluminium cylinder head, and an aluminium structural oilpan, able to support the front drive shafts. Even the pistons are lightweight with each one weighing just 454 grams!

The construction of the V6 engine is arranged around the two banks of cylinders at an angle of 75 degrees with a compact cylinder offset of just 32.5 mm. This allows the engine to be compact, with good vibration characteristics, eliminating any requirement for balance shafts and the related extra cost, weight and complexity.

The Engine Management System uses a 32 bit ECU processor and is Euro IV / E-OBD and LEV/OBDII compliant.