Optimum throttle response (a crucial ingredient in confirming the new Jaguar XK's sports car character) is delivered by full 'drive-by-wire' electronic throttle control, with no mechanical connection between the accelerator pedal and the throttle body. The response is based on the torque demand for every instantaneous driving situation. That is calculated by the electronic engine management control, based on parameters including the driver's accelerator input, and other vehicle factors such as road speed, engine speed and gear selection. The electronic controls then call up the required torque at any instant by adjusting throttle position, variable cam phasing, fuel flow and exhaust gas recirculation settings.

Equally important for its new role in Jaguar's sportiest cars, the 4.2 litre 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 Jaguar 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.


JAGUAR XK TRANSMISSION

The new Jaguar 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. Like the new XK's AJ-V8 engines, it is notably light and compact. 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.

Jaguar 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, also utilising an automatic blip of the throttle to maintain ultra-smooth downshifts.

For the first time in a Jaguar, drivers will be able to use steering wheel-mounted paddles to change gear. 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 power-on 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 Jaguar 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.

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