New XF moves to Jaguar's aluminum architecture

  • 09-Apr-2015 03:41 EDT
aei-jagXF-exterior.jpg

Jaguar XF moves to aluminum body, with a coupe-like look, but with increased rear passenger room, including up to 1.1 in greater headroom.

Jaguar's best-selling model, the XF, is moving from a steel body to the aluminum-intensive monocoque architecture used on the XE and XJ. It's one of the latest steps the luxury car maker has taken to meet regulatory and emissions demands in Europe and the U.S. The new car, scheduled for introduction in winter, was debuted to the public at the 2015 New York Auto Show. It's a midsize-plus model, fitting between the full-size XJ and the mid-size XE.

The car has a body-in-white that is some 75% aluminum, and much of that aluminum is RC5754, which is primarily scrap recycled with a small percent of new material. The recycled aluminum, which comes from Jaguar's press shops, constitutes much of the 5000 series wrought alloy (aluminum and magnesium) that is used on the XF, where specified to add stiffness (as for underbody reinforcements).

Steel used for weight distribution

Where steel is used, such as for the rear underbody, in the decklid, and rear-seat-area pan, it serves a number of specific engineering requirements, and it also contributes to a balanced front-rear weight distribution. The end result is a projected 51% front, 49% rear balance.

The steel applications pose an obvious galvanic-corrosion-protection requirement and Jaguar employs a five layer process based on aerospace techniques. First a zinc coating is applied to the steel. Then the joints are made with structural adhesive. Next, the entire body is electrocoated. Following that, seam sealer is applied, and finally the body is painted. There are no body welds, although self-piercing rivets are used.

The bodyside panels are stamped from single sheets of high-strength 6000-series aluminum alloy, which is a wrought alloy that contains magnesium and silicon. A panel weighs less than 6 kg (13 lb).

Jaguar uses specific high-strength aluminum alloys for front and rear crash structures and the A- and B-pillars. The front structure joint with the A-pillar is a large section shaped to distribute crash energy. The B-pillar also gets an ultra-high-strength (boron) steel reinforcement and is filled with high-density foam. The front suspension towers are high-pressure die-cast aluminum for added stiffness in that area.

Both the dashboard's cross-car beam and the hood crush beam are made of magnesium.

Precise riveting boosts rigidity

Assembling the side panels to the remainder of the body structure starts with precise locating of the rivets, so the overall result is a more torsionally rigid package. Jaguar claims up to 28% improvement, with the 2016 model specification at 21.7 kN·m (16,000 lb·ft) per degree.

Naturally a Jaguar has to be quiet and the best way is to ensure that is to design noise out. The crash structure behind the front bulkhead, for example, consists of sealed double-wall sections. Foam fillers are placed inside boxed aluminum sections, and when the body goes through the electrocoating ovens, the foam expands to fill. In other locations, sound deadening is a spray-on type that can perform the needed sound reduction with less added weight than mastic sheeting.

The XF is some 80 kg (176 lb) lighter than comparable competition, Jaguar claims, and 190 kg (419 lb) below the previous model with the steel body. Vehicle weight is 3902 lb (1770 kg) for the rear wheel drive model, 4145 lb (1880 kg) for the AWD.

Coefficient of drag was reduced from 0.29 to 0.26. An assist comes from vents in the front bumper that direct airflow smoothly over the front wheels, instead of becoming turbulent around the wheels and creating drag.

The new model is shorter than its predecessor at 195.1 in (4956 mm) long overall, on a 116.6-in (2962-mm) wheelbase. The wheelbase actually is 2.0 in (51 mm) longer, but overall length is 3.3 in (84 mm) shorter. Rear legroom is slightly greater, up 15 mm (0.6 in) to 951 mm (37.4 in). Despite the coupe look, headroom is greater by 1.1 in (28 mm).

There are two 3.0-L supercharged gasoline engines for the U.S. market, both using the same Eaton Roots-type supercharger. One is rated at 340 hp (254 kW) and 332 lb·ft (450 N·m), the other at 380 hp (283 kW) and 339 lb·ft (460 N·m). Both are bolted to the eight-speed automatic, which is required for pairing with all-wheel drive.

A six-speed manual is listed for rear-wheel-drive models and the 340-hp V6, but is not available at launch. A supercharged version of the 5.0-L V8 rated at 550 hp (410 kW) and 502 lb·ft (681 N·m) will be available with a forthcoming Type R performance model.

The electric power steering has been upgraded with improved sensing inputs, better damping steering response to both road irregularities and road camber. The AWD system transfer case is new, with a chain drive for lighter weight and smoother torque transfer vs. the previous gear-drive type.

Standard, optional suspension variants

The standard shock absorbers contain a second valve to provide velocity- and frequency- dependent damping. During moderate driving conditions, that valve is open and some hydraulic fluid passes through. This additional flow path reduces damping for a smoother ride. At increasing speed, the valve closes and all the fluid has to go through the piston valve, which firms up the ride for better control.

In addition, there's Jaguar's optional active damping system, which senses body movements 100 times/s and wheel movement 500 times/s. This electronic system has been improved for better control of damping at all speeds, and incorporates advanced algorithms for road texture detection to provide better traction. Like the F-Type, it can now be driver-configured at the control stack touch-screen.

The XF incorporates a standard advanced traction control system (All Surface Progress Control) that improves drive away on both rear-drive and AWD models in ice and snow. Also included with AWD is torque vectoring by braking, for which the vehicle's electronic stability control modulates torque-on-demand for varying weather conditions.

Integrated with AWD and the active damping system is Jaguar's Adaptive Surface Response. ASR employs algorithms for road-surface-texture detection and uses the information to modify steering response, transmission shifting, throttle response, and stability control operation.

The front suspension is an upgraded double-wishbone design modeled after the F-Type to improve cornering. The rear suspension drops the double-wishbone for a multi-link with an integral link that connects the toe link to the control arm. This separates vertical from lateral forces, so each can be tuned separately, for a better ride.

The XF has a full suite of optional safety features, including automatic emergency braking.   For connectivity, it offers the 10.2-in corporate capacitive touch screen with Incontrol Apps for a smartphone. This touch screen and the 12.3-in configurable TFT (thin film transistor) instrument cluster also are available on the Land Rover Range Rover.

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