Overview: Jaguar XJ

Jaguar’s new flagship XJ model made its global début at the Frankfurt International Motor Show on 15 September, 2009. According to Jaguar Cars Managing Director, Mike O’Driscoll, the new car was intended to ‘re-imagine’ the sporting luxury car.

On the surface, the new car’s styling is interesting, with echoes of old Bentleys (the nose), new Bentleys (the tail), and the Citroën C6 (the rear pillars). The design is a total departure, inside and out, from the former model, whose visual lineage back to the original XJ of 1968 was clear.

Technically, the new XJ is an interesting car — in the ‘virtual engineering’ technology used to design and develop it, and in its structure, which is notably free of steel parts. Here, we take a look at the most important aspects of the new Jaguar XJ’s design and execution.

Chassis and structure

The new Jaguar XJ is constructed largely from aluminium, with some magnesium and alloy sandwich components. There’s no steel used.

Bodyshell rigidity and lightness were priorities. The technology used for joining panels is inspired by aerospace practice, using bonding and riveting; to improve stiffness, the number of panel-joins is minimised by using large, relatively complex pressings in place of multiple smaller panels. Compared with the previous model, the new XJ uses 12 per cent. fewer rivets and 25 per cent. less adhesive. It also requires less energy to build.

Click here for more detail.

The aluminium bodyshell incorporates more than 50 per cent. recycled material, and Jaguar intends ultimately to increase this to 75 per cent. Body panels made from recycled material use only five per cent. of the energy required for new aluminium, giving a potential saving of three tonnes of CO2 per car. Aluminium is an energy-intensive metal to produce from its ore, but much less so to recycle; also, the metal can be recycled indefinitely without damaging its structure.

Novel high-strength aluminium alloys have been deployed at various points around the the XJ’s structure to improve stiffness and durability while also reducing the amount of material used. For example, a new material called Fusion — essentially a high-strength aluminium ‘sandwich’ — enables panel thickness to be reduced by 10 per cent. It is used for the wings, roof panels and boot lid.

The front-end carrier, which supports parts like the headlamps and grille, is a one-piece magnesium casting.

The decision to have a two-part glass roof meant that an unusual approach was needed for the structure of the roof and body-sides. A hydroformed aluminium tube section runs from the base of the A-pillar to the D-pillar, imparting considerable strength and rigidity to the bodyshell.

Jaguar
XJ 3.0D
Audi
A8 3.0 TDI
Quattro
BMW
740d
Mercedes
S 350 CDI
Length 5122 5062 5072 5096
Width 1894 1894 1902 1871
Height 1448 1444 1479 1485
Wheelbase 3032 2944 3070 3035
Front track 1626 1618 1611 1600
Rear track 1604 1605 1650 1606
Kerb mass 1796 1830 1950 1955
WB/L 0.59 0.58 0.61 0.60
Cd 0.29 0.27 0.30 0.26

In this table, we’ve taken a model at random from the new XJ range and compared its vital statistics with those of a handful of competitors. Comparing the kerb mass of the Jaguar with that of Audi’s aluminium A8 is interesting: the Audi is a fraction smaller and 34kg (two per cent.) heavier, but it drives all four wheels. The Jaguar is driven by its rear wheels only. How much would the Audi weigh if it were configured for rear-wheel drive? An impossible question.

So the XJ shell is light. Jaguar is also boasting about its strength. A combination of light weight and high torsional rigidity is a good route not only to decent efficiency but also to handling agility: the forces required to change a car’s direction are lower for a light car than for a heavy one.

The softness of aluminium is well understood. If you hit it, it not only bends but stretches, making aluminium body panels harder (or impossible) to repair after minor accidents. Jaguar has gone some way to addressing this in four vulnerable areas by bake-hardening the doors.

Like the very different McLaren MP4-12C sportscar we described recently, the new XJ is very much a product of virtual engineering — using detailed simulations to develop components and assemblies, and to gain insight into their long-term weaknesses.

Jaguar calls its virtual engineering techniques Virtual Process (VP) and Virtual Series (VS). The principle is easy to understand: designing a com­ponent, making a prototype of it, testing it, finding it inadequate, analysing its faults and creating a replacement takes a lot of time in the workshop and on the test-track. Additionally, analysing basic faults requires human engineering skills that would be better deployed in refining a system that’s almost right, where an engineer’s intuition is invaluable. But with enough com­puting power, you can create a virtual world in which a component can be designed and tested to destruction without the need actually to make it. This takes no workshop time or track time at all. Only when the basics are right, and the component or assembly is behaving well in simulation, is it created in the real world and tested on a real car. With the more basic problems sorted out in simulation, the engineers are free to use their instincts to refine the system.

In the case of the Jaguar XJ, the simulations apparently included roughly 40,000 quality-specific assessments, over a million virtual miles and 7000 crashes — before any physical prototypes turned a wheel.

Jaguar’s Virtual Reality Centre, tucked away at Jaguar Land Rover’s Warwickshire headquarters, is where it all happens. The four-walled virtual reality ‘cave’ allows engineers to visualise CAD models of vehicles and components as full-size 3D images, using eight high-definition projectors to create photo-quality images. Wearing 3D glasses, engineers can see their designs from any angle. This technology proved particularly effective at identifying potential conflicts with the routing of piping and wiring in the vehicle’s interior, allowing problems to be resolved very early in the design process.

For refinement, the XJ’s body features a double firewall and laminated glass in all the main windows.

Driving dynamics

Technologies that we first saw on the XFR and XKR models have been adapted for the new XJ. The full list of control systems that fine-tune the car’s dynamics takes a bit of reading: an anti-lock braking system of course, Dynamic Stability Control (DSC), Cornering Brake Control (CBC), Understeer Control, Electronic Brakeforce Distribution (EBD), Electronic Traction Control (ETC), Emergency Brake Assist (EBA), Engine Drag Torque Control and, for vehicles fitted with Adaptive Cruise Control (ACC), Electronic Brake Pre-fill.

A two-stage Dynamic Stability Control system is used. This combines the normal on-off switchable DSC function, which reacts as soon as it detects slip, with Trac DSC — this allows more slip before intervening, to give the driver a little more sense of the road. Pressing and holding the DSC button for 10 seconds fully disables the system.

Click here for more detail of the Jaguar XJ interior.

The driver can tailor the driving experience to suit their mood or the prevailing conditions. The Jaguar Drive Control offers two alternative driving modes (apart from the default settings): Dynamic mode and Winter mode. Each mode defines the characteristics of engine mapping, transmission shifts, Adaptive Dynamics and Active Differential Control systems and DSC interventions. Dynamic mode delivers later gear-changes and stiffer damper settings — and, in questionable taste we think, a different colour for the instrument lighting. Winter mode sets the transmission to pull away in second and delivers a more ‘interventionist’ anti-skid régime.

The engine’s air intake system has been tuned to deliver an ‘inspiring engine soundtrack’ when it’s driven firmly, but as little noise as possible while cruising.

Inside, the seat belts draw you in to the seat under heavy braking or hard cornering, and when Dynamic Mode is activated.

Cars fitted with either of the two supercharged engines feature Active Differential Control (ADC), which was introduced at the beginning of 2009 on the XKR and XFR models. This system uses a computer-controlled differential to distribute (or ‘vector’) torque between the rear wheels, operating like a more subtle and sensitive limited slip differential. The effect is to improve traction and dynamic stability. ADC uses an electronically-controlled multi-plate clutch in the final drive unit to vary the degree to which the differential locks, and thereby the proportion of torque sent to each driven wheel. The system responds to slip, detected by ABS sensors and yaw-sensors.

The Jaguar’s xenon headlamps are available with an ‘intelligent’ high beam system, which switches high beam on and off automatically according to the presence or otherwise of oncoming traffic and the prevailing lighting conditions. This feature is combined with adaptive lighting, which swivels the headlamps to follow the road when cornering, and also provides additional LED illumination when manoeuvring at low speeds.

Adaptive Cruise Control — a system seen recently on the Volvo S60 — measures the gap between the Jaguar and the vehicle in front. If the gap shrinks below a predetermined minimum distance, the cruise control system adjusts the XJ’s speed. There is also a radar-based blind-spot monitoring system that alerts the driver to vehicles in close proximity on either side, and a monitor for the inflation pressures and temperatures of the tyres.

The XJ’s suspension system is a development of the set-up used on the XK and XF. The front wheels are located by unequal length wishbones with weight-saving forged aluminium components; the springs are coils. The front subframe is directly mounted to the body — rather than being isolated by rubber bushes — to keep the steering response and handling sharp. The system is designed to deliver good straight-line stability and strong anti-dive characteristics under heavy braking. The multi-link rear suspension features lightweight cast aluminium links and is mounted on a subframe; it is essentially the same design that’s used on the XK and XF — with the significant exception that the XJ uses self-levelling air springs at the back.

Jaguar’s automated system for adjusting damper rates is called Adaptive Dynamics. Like many other systems, it monitors road conditions and the way the car is being driven and adjusts the dampers accordingly. Adaptive Dynamics was introduced at the beginning of 2009 on the XK and XFR models.

The new XJ inherits the braking system that was developed for the current XK. Diesel and atmospheric petrol XJs are fitted with 355mm discs at the front and 326mm items at the rear; the supercharged V8s feature 380mm front discs — with lightweight aluminium twin-piston floating callipers — and 376mm rears. All brake discs across the range are ventilated.

The automatic electric parking brake fitted to the new XJ engages automatically when the engine is shut off, releasing when Drive is selected. At junctions and traffic-lights, you can apply and release the brake manually using a little chrome control on the centre console.

For the first time on a Jaguar saloon, wider wheels with lower profile tyres are fitted at the rear of the car.

Powertrains

One diesel and three petrol engines are offered, with outputs ranging from 275PS to 510PS. One gearbox is used for all of the power-units — a shift-by-wire, six-speed automatic with an adaptive shift pattern. The box can be controlled by the Jaguar Drive Selector on the centre console or by paddles mounted behind the steering wheel. All XJ models are fitted with the Jaguar Sequential Shift system for manual gear selection.

The entry-level three-litre V6 diesel looks like the best all-rounder. Its 275PS seems rather modest next to the vaguely absurd outputs of the supercharged petrol engines, but the AJ-V6D’s twin sequential turbochargers provide 600Nm at 2000rpm. Jaguar claims the XJ diesel will reach 100km/h from a standing start in 6.4 seconds — there’s nowt wrong with that.

Jaguar’s AJ-V6D deploys two turbochargers that operate sequentially. This is not particularly unusual with inline engines, but it’s unique on a V-engine.

For most day-to-day driving, including motorway cruising, boost pressure is generated by a single variable-geometry turbocharger. Its companion — a smaller, fixed-geometry unit — is dormant. When the engine revs rise above 2800rpm, exhaust gases are fed into the smaller blower to increase boost.

Observant readers will have spotted that this is the reverse of the sequential turbocharging arrangements used by other manufacturers, which use the smaller turbine of the pair first.

The AJ-V6D’s common rail fuel-injection system delivers up to five injection pulses in each cycle at the commendable pressure of 2000 bar — common rail systems really are approaching unit injector territory now.

Conventional oxidation catalysts and particulate filters are used. NOx levels are controlled well enough by the exhaust gas recirculation system to render after-treatment unnecessary.

The three petrol engines are all directly-fuelled five-litre V8s. Jaguar’s new direct-injection 5000cc AJ-V8 engine was introduced at the beginning of 2009. It features a compact and lightweight all-aluminium design, and Jaguar claims that it suffers very low levels of internal friction. The engine features an industry-first: a centrally-mounted, multi-hole, spray-guided fuel injector, which delivers fuel at a pressure of up to 150 bar (15.0MPa) directly from the centre of the combustion chamber.

The V8s feature a new variable camshaft timing system. Rather than being operated by oil pressure, Jaguar’s VCT system is activated by the positive and negative torques generated by opening and closing the intake and exhaust valves. This has allowed a smaller engine oil pump to be used.

The 510PS and 470PS supercharged engines are fitted with a sixth-generation, twin vortex supercharger. This is a Roots-type unit, with counter-rotating, interleafing blades. Its high-helix rotor design increases the unit’s thermodynamic efficiency by a claimed 16 per cent. over its predecessor; it is also quieter.

Infotainment

We’ve long been concerned that upmarket cars are acquiring more control systems than can be dealt with safely on the fly. The previous Jaguar XJ dashboard was a magnificent throwback to the late sixties original, but with far more buttons. Even with familiarity, the middle bit of the dashboard was best approached with the car parked.

Previous XJ dash had a lot of heritage and a lot of buttons. Click here for more detail of the Jaguar XJ interior.

The new XJ features the kind of control system we see on most executive cars now: a touch-screen display on the dash for vehicle functions and navigation. But there is something very odd about the Jaguar’s command screen: what the driver sees displayed can be completely different from what the passenger sees.

It’s called Dual View, and it is a Bosch creation. The driver gets a navigation display or vehicle system settings, while the passenger can watch a DVD or control an i-pod.

The touch-screen ‘head’ unit in the Jaguar XJ communicates with other vehicle systems and functions using a central MOST network (Media Oriented System Transport) and a CAN bus (Controller Area Network). The unit makes it possible to prioritise the screen contents according to the current driving conditions. This should make operation more intuitive.

Bosch head unit can display two things at once. Click here for more detail of the Jaguar XJ interior.

For example, the navigation menu will appear if the GPS issues a route instruction. Any other display information will be suppressed during that time, with the exception of incoming phone calls.

Jaguar XJ 3.0D V6 275 5.0 V8 385 5.0 V8 470 5.0 V8 510
Swept volume 2993 5000 5000 5000
Compression
ratio
16.0 11.5 9.5 9.5
Valves 4 4 4 4
Bore/stroke 84.0/90.0 92.5/93.0 92.5/93.0 92.5/93.0
PS/rpm 275/4000 385/6500 470/6000 510/6000
PS/l 92 77 94 102
Nm/rpm 600/2000 515/3500 575/2500 625/2500
Nm/l 200 103 115 125
Combined MPG
(l/100km)
40.1
(7.0)
24.9
(11.4)
23.4
(12.1)
23.4
(12.1)
Cd 0.29 0.29 0.29 0.29
The new Jaguar XJ has a certain elegant brutality about it.

Whole-life energy auditing

Jaguar is one of the few car manufacturers to have embarked on a life-cycle energy audit for one of its cars. The Company submitted the new XJ for certification through the U.K. Vehicle Certification Agency; it has achieved its aim, in the process gaining insights into how future Jaguars could achieve improved environmental footprints.

The certification process looks at every element of a car’s life: development, manufacture, use over a defined lifetime — in this case 200,000km — and finally disposal and recycling. Every detail is examined, including the transport of components during the manufacturing process.

The auditing process takes account of the principles, requirements and guidelines for life-cycle assessments as set out in the international standards ISO 14040:2006 and ISO 14044:2006. It also too account of evidence of the integration of environmental aspects into the vehicle’s design and development as described in ISO TR 14062:2002.

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