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2007 Jaguar XK Convertible


Also like the XK it replaces, the all-new XK will be available in both two-door Coupe and Convertible forms, each model in its own right developed in parallel under one umbrella program. The decision to give the Convertible version a classic soft-top rather than a folding hard-top means the open option offers exactly the same 2+2 seating layout, without compromising the elegant lines of the rear body, the strong, rising waistline or the light weight of the car.

Three-Layered Roof

The fully-lined triple-layer roof has exceptional wind and road noise isolation. It opens and closes at the touch of a button in less than 18 seconds, and when dropped it stows neatly below a rigid aluminum tonneau cover without unacceptable intrusion into the large luggage space. Furthermore, the loadspace can be increased by approximately 3 cu. ft. (83 liters) by stowing the retractable loadspace separator when the Convertible roof is up. The use of a soft-top has also allowed the exterior body to be designed with much cleaner lines and a relatively low deck, meaning the door waist line can be carried right through the vehicle from the front of the car to the tail.

The roof is constructed from three layers, which also insulate against wind and road noise. The outer layer is a completely waterproof cloth/rubber/cloth laminate, and the inner layer is a luxurious cloth lining which is taut and smooth when the roof is closed. The ‘sandwich filling’ is an insulation layer, using 3M Thinsulate material. This gives significantly better insulation for less than half the thickness of the previous XK soft-top construction. It is not only lighter, it takes up significantly less volume when the roof is stowed, allowing more space for passengers and luggage. The rear window is toughened glass, with a heating element, and is bonded into the roof. The door glass automatically drops slightly as the doors are closed, and rises again to seal inside the roof water channels. Additionally, the Convertible’s rear windows can be lowered even when the roof is up.

The soft-top is raised and lowered by a single press of a button, using hydraulic actuators and electronic controls. It will go from fully open to closed in under 18 seconds, which includes automatically raising the side windows and rear quarter glasses at the end of the cycle.

When the soft-top is up, the profile has sleek, elegant lines and the ‘C’ pillar area visually fits comfortably over the rear wheels. Attention to detail is continued with a chrome finishing strip fitted to the door capping and continuing around the soft-top base.

The new XK was created by Jaguar’s new design team under the leadership of Design Director Ian Callum, to push Jaguar deeper into the 21 st century. The new XK’s lines are bold and beautiful, powerful but elegant. In Ian Callum’s words, it looks “just like a Jaguar should – powerful and exciting. That power comes from a sense of tension, muscle and form and is very much part of the new design language we are creating.”

That new language begins with the proportions and stance, which are dramatically different from those of the previous XK. The new car sits on a longer wheelbase but it has markedly shorter overhangs, so it is very little longer overall. Its width, strong, high waistline and short, powerful haunches give an impression of a car hugging the ground, crouched, ready for action. With its dynamic hood and roof lines it looks much more compact, more contemporary, and extremely muscular and athletic - suggesting movement, power and agility even when it is stationary.

Although the new XK looks very compact, it has excellent luggage space, and the Coupe is designed to be able to carry two golf bags. Although the rear overhang is fully 4.8 inches shorter than on the previous XK, the rear luggage volume is only 0.28 cu. ft. less, or 0.78 cu. ft. more when the optional runflat tires are specified – and of course it has gained the enormous benefit of the all-new Liftback design, which provides excellent access to the loadspace area.

“I am very proud of the new XK,” says Ian Callum. “It is contemporary with wonderful modern proportions yet we have succeeded in integrating design cues from our heritage. The front grille, for example, is pure E-type, and makes the perfect statement that this is, first and foremost, a Jaguar.”

The Naturally Aspirated 4.2-liter V8 Engine

A key element in the character of a sports car is its engine. The new XK will be launched with a powerful four-cam naturally aspirated 4.2-liter AJ-V8 powerplant. This compact, lightweight engine is based on that fitted to the latest generation XJ saloon and has undergone significant development compared with the engine used in the previous XK, including new fuel-injection technology. The latest 4.2-liter engine satisfies stringent US ULEV II emissions regulations.

The naturally aspirated 4.2-liter V8 engine produces 300 bhp and develops maximum torque of 303 lb-ft at 4,100 rpm. Again, the spread of torque is an important ingredient in the XK’s effortlessly sporty character, and this engine delivers more than 85 percent of torque all the way from 2,000 to 6,000 rpm. Yet it still offers fine fuel economy and low emissions figures, with a drop in CO2 emissions of five percent.

The naturally aspirated 4.2-liter V8 XK Coupe has an electronically limited maximum speed of 155 mph (250 km/h) and a 0-60 mph time of 5.9 seconds, plus instant throttle response and broad flexibility for punchy performance across the range. With the new XK’s weight savings, the new naturally aspirated 4.2’s standing quarter-mile time of 14.4 seconds is less than half a second off the pace of the previous supercharged 4.2 XKR.

The latest AJ-V8 engine was developed to satisfy ULEV II, as well as strict European emissions requirements. That means a 50 percent reduction in hydrocarbons (HC) and oxides of nitrogen (NOx) and a 60 percent reduction in carbon monoxide (CO) emissions. It features Exhaust Gas Recirculation and the latest generation of catalyst cores with thinner coatings of higher density catalysing material – which reduces exhaust gas restriction and is more efficient.

The compact AJ-V8 engine has very stiff but lightweight all-aluminum construction, with eight cylinders in a 90-degree ‘V’. The combination of strength and lightness begins with a ribbed cylinder block and cylinder heads. The 4.2-liter version has bore and stroke of 3.39 x 3.56 inches for a capacity of 4196cc. The fully balanced four-throw, six-counterweight crankshaft is supported in five main bearings. The connecting rods use split-fractured big-end journals for strength with light weight and perfect balance. Each cylinder head carries two chain-driven overhead camshafts, which are hollow, to save weight and improve performance by allowing higher engine speeds. The camshafts operate four valves (two inlet and two exhaust) in each pentroof combustion chamber, around a central spark plug. An unusually narrow 28 degree included valve angle allows a compact combustion chamber shape and narrower heads, which benefits overall packaging.

Equally important for its new role in Jaguar’s sportiest cars, the 4.2-liter engine has been engineered to give the sound expected from a real sports car engine – especially under acceleration – but without being undesirably noisy. The new XK’s Semi-Active Exhaust system varies the flow of exhaust gases through the main, large silencer box depending on the pressure in the system, and features acoustically tuned tailpipes that eliminate low speed boom. There is also an underfloor resonator with two chambers (one for each cylinder bank) which balances the sound from the two banks. By tuning the sounds from the air-induction system and the exhaust system, Jaguar concentrated on both the solid, powerful low-frequency sounds and more technically ‘sophisticated’ higher frequency sounds, to give a feeling of power and performance.

The Transmission

The XK uses the latest version of Jaguar’s class-leading six-speed epicyclic automatic transmission, which is widely regarded as one of the best automatic transmissions in the premium, sports car market. It features Bosch Mechatronic shift – an electro-hydraulic shift mechanism whose adaptive shift strategy responds to both road conditions and driving style, to give the smoothest shifts with optimum performance.

The XK’s transmission introduces a new generation of automatic gearshift for Jaguar, replacing the familiar ‘J’ gate with the Jaguar Sequential Shift system with Park, Reverse, Neutral, Drive and Sport modes. The fully automatic Drive mode adapts to individual driving styles, while a Sport Auto mode can also be selected. This offers an even more responsive fully automatic shift strategy.

For the first time in a Jaguar, drivers will be able to use steering wheel-mounted paddles to change gears. In either Drive or Sport modes instant access to manual operation is achieved via the shift paddles. In manual mode, the transmission controller uses an alternative parameter set to control gear shifts, enabling delivery of extremely rapid and responsive manual shifts, whilst maintaining class-leading Jaguar shift quality in automatic modes. Interaction with the torque-based engine management system allows for precise torque control during shifts – engine inertia is used to enhance acceleration during upshifts, and an engine torque increase (‘throttle blip’) is used to significantly shorten over-run downshifts.

The epicyclic geartrain utilises clutch-to-clutch synchronous shifting to ensure that a controlled amount of torque is always being transferred during power on upshifts. This makes the shift much smoother than in the automated manual gearboxes adopted by some of the new XK’s competitors, where the use of an automated clutch completely interrupts the flow of torque during shifts.

The extremely rapid shift times often quoted for automated manual transmissions relate solely to the duration of this torque interrupt. The true shift time is significantly longer, since the clutch must be disengaged prior to the ratio change, and re-engaged after. In contrast, the Jaguar Sequential Shift suffers no torque interrupt resulting in a smoother more powerful shift feel, and a very short total shift time of approximately 600 milliseconds from the driver touching the shift paddle to the completion of the shift event.

In fact, during development, comparison tests between Jaguar Sequential Shift and rival automatic transmissions in the class showed the new XK’s transmission to be the fastest system of all, changing gear at least 400 milliseconds faster than a standard automatic and 100 milliseconds faster than the best automated manual system.

Lightweight Vehicle Technology

Key to the all-new XK’s character is Jaguar’s industry-leading bonded and riveted aluminum monocoque body structure, introduced with the latest XJ saloons. The aluminum body incorporates the latest thinking in epoxy bonding and riveting techniques to produce a chassis that is very safe, as well as very light. In fact the new XK’s aluminum chassis is significantly lighter and stiffer in both Coupe and Convertible form than the steel model it replaces – over 30 percent stiffer and an impressive 50 percent stiffer respectively.

As a consequence the new XK accelerates faster, uses less fuel and produces lower emissions than the model it replaces, while offering high levels of safety, reduced noise and vibration intrusion, and improved ride and handling characteristics thanks to improved suspension dynamics.

Jaguar’s Lightweight Vehicle Technology is unique in the industry as a complete aluminum monocoque body structure as distinct from an aluminum spaceframe with separate aluminum panels. Developed from aircraft industry methods, where strength is critical for huge temperature variations and very high stresses during take-offs and landings, Jaguar’s manufacturing process produces a massively strong but very light structure. The new XK takes the concept a step further with extended use of lightweight aluminum castings and extrusions as well as the pressed aluminum panels. Its strength and light weight come from the way the shell is constructed, using new jointing technologies developed by Jaguar and its suppliers.

There is only a single welded joint in the new XK Coupe body, the one ‘cosmetic’ joint on the roof. That also has an environmental benefit in that the body construction needs no high electrical current, produces no welding sparks or fumes, and needs no water for cooling. All the other joints in the new XK shell are formed using Jaguar’s unique combination of riveting and bonding. Most joints are produced using self-piercing rivets applied by hydraulic pressure against a fixed tool. Where access to only one side of the joint is possible, as in some of the new extruded box sections, a new riveting process has been developed; and where particularly high stiffness is required in a joint, a combination of riveting and bonding is used – with the adhesive bond in effect creating a continuous joint which is stronger than a similar, riveted-only joint. All visible exterior panels are bonded to the underlying structure, and a new automated seam-sealing process seals all relevant areas of the shell before painting, to ensure that no gaps are missed.

In the new XK, a secondary front bulkhead of aluminum and composite materials helps reduce transmission of noise from the engine compartment and provides a dry area under the hood for accommodating electrical components. The new structure also has benefits in refinement; castings are used for the mounting points for the engine, transmission and suspension make those points significantly stiffer, further reducing transmitted noise and helping to improve suspension dynamics. In terms of long-term strength, Jaguar’s all-aluminum shell has durability approaching twice that of a traditional spot-welded steel body.

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