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Engineering - (Global)

August 28th, 2007





Underlying the new visual design language, the XF is the product of a new generation of design technology, materials and manufacturing opportunities, as Phil Hodgkinson, Jaguar Programmes Director, explains:

"The engineering disciplines behind the XF are as ground-breaking as its new design language. New development processes and computer tools allowed us to work through the programme at a quicker pace than anything previously; new technologies and materials combine strength with lightness; and Jaguar craftsmanship, too, has explored new, exciting contemporary avenues."

Virtual Process (VP) and Virtual Series (VS) are the cutting-edge technologies used by Jaguar to take the XF from concept to reality. These techniques use massive computing power and sophisticated modelling programmes to create components and even whole vehicles in the virtual world, before building physical parts and perfecting the systems and processes to manufacture the car. The XF represents the first time that VP and VS tools have been used by Jaguar throughout a complete vehicle programme - from vehicle development, to production feasibility studies, to build planning.

But VP also dramatically improves overall quality, by allowing rapid sign-off of component designs, and eliminating the early physical prototype stage. With VP, when prototypes finally are built, they are intended only to validate what is already known, not to develop areas that are still unresolved. Fully representative vehicles are used for physical evaluation, including on-road testing, crash-testing, hot and cold climate testing, and durability testing. At the same time, the VS programme is working on everything that is needed eventually to build the car - leading to significant improvements in craftsmanship, efficiency, even long-term serviceability.

New technology is also key to the XF's construction. It was the first programme within Jaguar to use the next-generation CAD programme C3PMG, which combines an all-new CAD-modelling software package with an all-new data-management package - opening the way to exceptional strength without unwanted weight. The design is led by safety needs, especially by the latest side intrusion and SUV over-ride requirements. The reinforced passenger safety cell incorporates new thinking from the lower side rails up.

The XF adopts the latest generation steels, especially in the upper body - including high carbon steels, dual-phase, hot-formed boron steels, and bake-hardened steels to form a vertical safety 'ring' around the occupant cell. As well as combining strength with lightness, these steels improve corrosion resistance, by making best use of zinc and improving e-coat paint flow - and new thinking means that in spite of their strength, the XF's A and B-pillars are impressively slim, to the benefit of both visibility and accessibility. Similarly, the lower sills are the first component on any Jaguar to use incredibly strong, dual-phase DP600 steel.

Second-generation Pedestrian Contact Sensing System - the acclaimed safety system introduced by Jaguar on the XK - is included on the XF. This can mitigate pedestrian injury by firing actuators that deploy the bonnet, resulting in a cushioned space between the bonnet and engine hardpoints. The system builds on the technology proven in the XK, using higher resolution sensing and an active rear-hinged bonnet.

Every XF also comes with two-stage driver and front passenger airbags, side and curtain airbags and Seat Occupant Sensing systems to help ensure the airbags work precisely and only as needed in every circumstance. Front-seat occupants also have the added protection of an Anti-Whiplash System and 'soft-landing' technology in the seat-belt retractors to soften contact with the front airbags.

Other changes - many of them made possible by extensive use of the Virtual Process during the development programme - improve craftsmanship by optimising the manufacturing process. Close attention to optical quality creates the smallest, most consistent panel gaps and other new measures improve resistance to minor impacts, making accident repairs easier and less expensive, so contributing to significant cost-of-ownership benefits.

SUSPENSION

The XF's class-leading torsional rigidity has significant benefits for refinement and provides the perfect platform for a suspension system that is a further development of the XK sports car, and delivers a ride/handling balance and steering characteristics absolutely in line with the XF's sporting looks. Unequal length wishbone front suspension with weight-saving aluminium components, and multi-link rear suspension are both subframe mounted for maximum control, including excellent straight-line stability and strong anti-dive characteristics under heavy braking, with minimum road noise and vibration.

The only suspension variations on the XF are between the V6 petrol, V6 diesel and V8 naturally aspirated models, which all use finely tuned passive suspension, and the SV8, which uses Jaguar's Computer Adaptive Technology Suspension (CATS™). The latest CATS™ is a sophisticated system shared with the new Jaguar XK sports grand tourer. It uses electronically controlled, two-stage, adaptive dampers whose characteristics are automatically adjusted within milliseconds in response to road conditions and driving inputs, for the optimum balance between comfort and control.

BRAKES

The XF uses large 326mm x 20mm vented front discs on all naturally aspirated models and 355mm x 32mm vented front discs on the SV8 model for powerful, balanced braking performance. The rear discs on all versions measure 326mm x 20mm.

An extremely stiff pedal box contributes to a particularly solid pedal feel, and the brake assistance is tuned to give a very progressive feel, while softening the initial response.

The XF uses Jaguar's Electric Parking Brake, with a small and neat, chromed release in the centre console. As the XF's braking system communicates electronically with the shift-by-wire technology of the JaguarDrive Selector™ function, so the Parking Brake is released automatically as Drive is selected - although the Parking Brake can also be engaged and disengaged manually if appropriate, through the release.

STEERING

Variable ratio power-assisted steering is standard on every version of XF, for reduced parking effort at low speeds and greater precision and feedback at higher speeds - and especially for positive weight to the on-centre feel, which is part of the new dynamic flavour. Steering effort at manoeuvring speeds is also reduced on diesel models.

The new XF adopts an electronic steering column lock - for compatibility with passive entry mode and the Jaguar Smart Key System™.

The XF's steering wheel includes cruise-control, JaguarVoice™ (where fitted) and audio controls - including volume, and radio channel pre-sets. The source button toggles through AM/FM/CD, plus any external device functions. The select buttons allow features such as CD track change, radio channel pre-set selection or iPod® or MP3 track change if such a device is in use.

WHEELS AND TYRES

The XF is available with 18, 19 or 20-inch wheels; the SV8 being the only car in its class to have 20-inch wheels as standard. All are cast in aluminium alloy and every design combines maximum strength with minimum weight. All cars carry the same specification of 18-inch diameter alloy mini-spare.

DRIVER AIDS

The XF's main control module governs many key safety functions including Emergency Brake assist (EBA), Electronic Brakeforce Distribution (EBD), Anti-lock Braking System (ABS), Traction Control through engine and brake intervention, Dynamic Stability Control (DSC), Cornering Brake Control (CBC) and Engine Drag Torque Control (EDR). And for the first time, the XF adds Understeer Control Logic, which has been designed to mitigate understeer by intervening through the engine management and braking systems to decelerate the car and help restore grip to the front wheels.

A two-stage DSC system similar to that featured on the new XK is standard equipment. It combines the normal on-off switchable DSC function, which reacts as soon as it detects slip, with Trac DSC, which allows more slip before intervening - better for a more sporting driving experience. It also allows a degree of wheel overspin on deep soft surfaces, which is essential for running with snow chains. The system defaults to normal 'DSC on' with each ignition-on sequence.

In Dynamic Mode (SV8 only), pressing and holding the DSC button fully disables the system, allowing an experienced driver to exploit fully the capability of the chassis, where conditions allow. Mode selection is confirmed on the instrument cluster display.

Also new on XFs fitted with Adaptive Cruise Control (ACC) is Electronic Brake Prefill. This senses any rapid throttle lift-off and initiates a small brake hydraulic pressure build-up in anticipation of the brakes being applied, to give better pedal response and slightly shorter stopping distances.

JaguarDrive Control™ offers different modes that interact with the DSC system, engine and gearbox, to change the characteristics of engine mapping, transmission shifts and brake interventions depending on driving conditions and circumstances. On naturally aspirated cars JaguarDrive Control™ has Normal and Winter modes, on the SV8 model there are Normal, Winter and Dynamic modes - the last of these to allow a more purposeful driving style.


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