Body language

The mildly evolutionary shape of the new seventh-generation XJ saloon disguises Jaguar’s most advanced body structure ever.

The car uses an advanced all-aluminium bodyshell, a first for Jaguar.

The launch, at the Paris Motor Show yesterday, comes 34 years to the day after the original XJ6, and coincides with the unveiling of Audi’s second-generation A8, also all-aluminium.

But Jaguar is claiming an industry first for its use of rivet-bonding joining technology for the whole body structure. The firm decided on the radical move to counteract the inexorable increase in bulk affecting cars in the luxury sector, as levels of equipment continue to grow.

The bodyshell is estimated to be 40 per cent lighter than the equivalent steel structure, which makes the new car up to 200kg lighter that the outgoing model. This has a knock-on benefit on performance and fuel consumption.

The body uses self-pierced rivets in combination with aerospace-sourced epoxy adhesive to join the aluminium pressings, castings and extrusions. The structure is primarily a conventional monocoque with castings and extrusions used locally to reduce the overall panel count. A magnesium cross-beam is included to support the facia and instrument panel.

The rivets are installed through the panels and the adhesive bead; the adhesive is heat-cured in the paint ovens during body painting. Jaguar says the cycle time for installing rivets is equivalent to spot-welding but the resulting joint has superior performance, for example against fatigue.

The result is a bodyshell that Jaguar says is 60 per cent stiffer than its predecessor, providing advantages in refinement and handling.

The new car will have self-levelling air suspension across the range, partly to compensate for the fact that the occupants represent a relatively higher proportion of the overall weight.

It also has an updated version of Jaguar’s computer active technology suspension to optimise ride and handling, traction control, and Dynamic Stability Control, which detects and responds to oversteer and understeer.

Adaptive cruise control maintains a safe distance from the car in front, and can provide an audible warning to the driver even when cruise control is switched off.

Sidebar: The Audi a8: ‘the lightest in its sector’

Audi’s A8 uses the third generation of its Audi Space Frame, which differs from Jaguar’s XJ in that the exterior panels are not part of the primary structure. Nonetheless, the company claims it is the lightest bodyshell in its market segment.

It builds on experience of the first-generation A8, introduced in 1994 after a 10-year development programme with Alcoa, and the more recent A2. The number of components has been reduced (from 334 to 267) from the previous A8, by greater use of castings and extrusions. A combination of riveting and various welding techniques, including a laser/MIG hybrid system, is used to assemble the structure.

Assembly of the simpler structure can be more automated, allowing Audi to increase annual output from 15,000 to 25,000, compared with Jaguar’s aim of at least 30,000.Audi also claims torsional rigidity is increased by 60 per cent, and like the XJ the A8 features electronically variable air suspension and adaptive cruise control.

A new feature is ‘one-touch personalisation’, in which a sensor pad can detect up to four drivers’ fingerprints and store them along with their preferences for positions of seats, mirrors, steering column and air-conditioning settings.

On the web