Jaguar revises XF diesel, uprates XKR

  • 11-Jul-2011 04:54 EDT
JAG7-11 XF  3.jpg

Jaguar's midlife update of the XF includes a new diesel and a reprofiled hood, a larger and more upright grill, and slimmer headlamps.

The figure 2.2 is becoming established in the European premium-car market as an essential part of a diesel-engine downsizing equation that indicates the route toward achieving a satisfactory level of power, performance, positive emissions levels, and parsimonious fuel consumption.

The Mercedes-Benz 250CDI's 500-N·m (369-lb·ft), 150-kW (201-hp) bi-turbo engine (classed as a 2.2 L in Germany but actually slightly smaller at 2143 cm³) is a leading example and is fitted to C-Class, E-Class, and even S-Class models. It can be linked to a seven-speed 7G-Tronic Plus automatic transmission.

Now Jaguar has decided to fit a 2.2-L diesel beneath the freshly sculpted hood of its latest XF.

Producing impressive levels of torque and power, but with only one turbocharger (an additional low-inertia turbo would improve the car’s step-off time), the engine, designated i4D, is the third generation of a power unit that is based on fundamental architecture that came initially from PSA Peugeot Citroën for lateral installation. When Ford partnered with PSA on diesel-engine development, it was used by Land Rover (then a Ford-owned company), although Jaguar’s now defunct X-Type was offered with Ford-sourced 2.0- and 2.2-L units.

Now, at last, Jaguar has taken the PSA unit, turned it through 90 degrees for longitudinal installation, and extensively re-engineered it for greater efficiency, lower noise levels, and stop/start operation. Mated it to an eight-speed ZF automatic transmission, the company expects it to overtake its V6 diesels in terms of market share.

Power output is 140 kW (188 hp) at 3500 rpm and maximum torque 450 N·m (332 lb·ft) at 2000 rpm; NEDC (New European Drive Cycle) combined CO2 emissions and fuel economy are 149 g/km and 5.4 L/100 km, respectively. Zero to 100 km/h (62 mph) takes the XF 8.5 s and top speed is 225 km/h (140 mph).

As XF Chief Program Engineer Andrew Whyman had the task of overseeing the engine’s installation as the most significant aspect of the midlife update of the XF range. “It had to reflect the Jaguar DNA found on all other models in our range," he said. "Jaguar characteristics include very good performance, refinement, low cabin noise levels under all conditions, and thorough refinement, now including stop/start operation, which is a first on a car of this type.”

Weight saving, enhanced combustion efficiency, and new materials have all played a part in achieving required targets.

The stop/start operation on a diesel with automatic transmission was a particular challenge, and Jaguar worked with Denso to meet it. “There must be no unusually complex information exchange with the end user other than the indication, via a green icon, that the system has gone into stop/start operation," said Whyman. "When the engine restarts, the icon is extinguished.”

To make the system as smooth, quiet, and unobtrusive as possible, a tandem solenoid starter system is used. “It incorporates a flywheel ring gear starter motor, but the use of a twin solenoid system provides far greater control of speed of engagement of the pinion into the ring gear," explained Whyman. "Benchmarking work showed that our restart response times were the fastest—in only 300 ms. We ran 200,000 cycles to prove the system.”

The most difficult stop/start phase to tackle while providing required refinement was suddenly needing to move away again as the engine and vehicle stopped. “RPM has then dropped to a point where simply refueling the engine alone will not restart it because it has insufficient momentum—and there would be a nasty meshing noise as the starter pinion fired into the just rotating ring,” stated Whyman. “But our engine management has been modeled to match engine and pinion speed. We know the speed of the pinion and can engage it to the rotating engine, so the engine does not have to return to zero revs for a restart. It was very, very challenging.” The 2.2-L diesel’s restart time will never exceed 900 ms even when the most extreme restart demand occurs, added Whyman.

As the Jaguar’s engine switches off when the car is stationary, so the ZF transmission disengages drive without the driver needing to manually select Neutral or Park. It re-engages as the driver releases the foot brake. The transmission has 200-ms shift speed and multiple change capability (i.e., directly from fifth to second).

A further link between stop/start and transmission is the introduction of “Easy Off.” A possible danger with stop/start systems is when a driver halts the car and exits it without pushing a stop button and leaves the ignition key fob in the vehicle believing the engine has stopped (which it has), but it may restart as the battery needs recharging. To overcome this, the XF monitors seatbelt buckle unlatching, door handle operation, and door opening to confirm that the driver has vacated the vehicle. The system's management then shuts down the ignition system and puts the transmission into Park.

“We believe we are the only company to do this. It is all about software, there are 10 key modules involved, and it’s patented,” said Whyman.

As for other significant changes to adapt the powertrain for use in the XF, they include engineering the crankcase and engine-mounting strategies for longitudinal installation. All ancillary mountings are re-engineered and optimized, including structural and acoustic damping. Piston mass and piston ring loads are reduced, and low-voltage glow plugs are used. Bearings are optimized for reduced rotational friction. The engine has an unusual combination of a stainless steel exhaust manifold and water-cooled variable geometry Mitsubishi turbocharger plus closed loop exhaust gas temperature control augmented by exhaust gas recirculation (EGR). Replacement of cast iron camshafts with hollow steel ones incorporating sintered cam lobes saves about 1 kg (2.2 lb). The double-walled sump has internal rubber sound deadening and internal honeycomb structure within the front timing cover. Some 75% of the engine’s radiating surfaces have been re-engineered or modified to reduce noise.

The result of all this is an impressively quiet solution but with sufficient aural feedback under hard acceleration to the cabin to mark it out as a premium sports sedan.

The car has received extensive detail changes including a slimmer headlight design with LED DLR (daylight running lamp) strips; a larger, more upright grill; and a lower, reprofiled hood and air vents at the side of the front fenders. Interior changes include redesigned seats. The 5.0-L XFR gets triple front air dams and hood vents.

In other Jaguar model news, the XKR has gotten an upgrade to XKR-S status. The supercharged Jaguar XKR is a very quick car, but the new XKR-S with 10% more power and torque is even more so.

“We wanted to turn up the volume of all aspects of the car: performance, dynamics, and visual, both external and internal," said Russ Varney, Chief Program Engineer, Jaguar Cars. "It’s no use just turning up one of those because you spoil the overall harmony and it will feel ‘disconnected’.”

Power output is 405 kW (543 hp), maximum torque 680 N·m (502 lb·ft), and top speed 300 km/h (186 mph), with a 0-100 km/h time of 4.4 s and 0-160 km/h (0-99 mph) in 8.7 s. CO2 emissions are 292 g/km. EU curb mass is 1753 kg (3865 lb).

Ride height is reduced 10 mm (0.4 in); front and rear spring rates upped; adaptive dynamics tuned for reduced pitch and roll, and front suspension gets new, stiffened uprights and revised geometry.

A CFD-developed aerodynamics package sees overall lift reduced by 26% with improved lateral aerodynamic stability.The car also gets an active exhaust system.

“In the five years since the aluminum-bodied XK was introduced, it has been steadily evolved. We had some technology headroom at the beginning of the program, but we have been surprised at just how far we could go with design and engineering enhancements," said Varney. "We have not had to do anything with regard to body stiffness, which remains at 21,000 N·m per degree. With the XKR-S, that stiffness is being exploited to its full extent. Front suspension spring rate is much stiffer (about 28%) and we achieve enhanced steering response. The front upright (knuckle) has been redesigned with greater camber stiffness. Its mass has been increased, but this is fully offset by lighter wheels and tires. Geometry changes give keener turn-in and response.”

Engine changes were relatively modest. “There was some latent performance in the XKR engine," said Varney. "It’s been recalibrated by playing with the ‘noughts and ones.’ We do have different spark plugs and have increased the fueling, but we have not increased the supercharger speed. The calibration is now cut off at 300 km/h rather than 255 km/h.” The car has been tested at speeds above 300 km/h.

The current XK range’s successor is now in development. Although it is expected to have a different architecture, as would be expected, there will be some sharing of technology with other Jaguar models to support the business case. Aluminum remains Jaguar’s material of choice, although others would be used “where appropriate,” explained Varney. “We have spent a lot of time improving our use of aluminum; it was not the easiest of materials with which to work, but we are through that and are now expert in its use." The XKR-S’s body shell weight is 285 kg (628 lb).

Commercially constrained by what he can reveal about future models, Varney said that hybridization had potential but that it was a question of what level was apposite to a Jaguar.

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