Jaguar remakes XJ

  • 04-Mar-2010 06:06 EST
jaguar XJ 2 2-10.jpg

The new generation Jaguar XJ is being produced with a single worldwide body specification.

The new XJ sedan advances Jaguar's aluminum design and manufacturing philosophy.

With its new-generation XJ, Jaguar has taken the radical step of departing from a retro-based style that had visual cues reaching back to the Series I of 1968. But it is not just its external looks that have changed. Although incorporating elements of the outgoing model, the new car uses a raft of technologies not only to meet market needs and opportunities but also to achieve major manufacturing efficiencies.

Applying its lightweight vehicle (LWV) strategy, Jaguar hopes to strengthen its position in the premium sector via wide-ranging engineering solutions created to meet its design and manufacturing objectives.

Entering production now, the aluminum-bodied car will be built in regular 3032-mm (119.4-in) and long 3157-mm (124.3-in) wheelbase forms and offer a choice of three 5.0-L V8 gasoline engines: supercharged, 375 kW (503 hp), 625 N·m (461 lb·ft), 289 g/km CO2 emissions; supercharged, 346 kW (464 hp), 575 N·m (424 lb·ft), 289 g/km; and naturally aspirated, 283 kW (380 hp), 515 N·m (380 lb·ft), 264 g/km. A 3.0-L V6 diesel, with sequential twin-turbo technology, cam-profile switching, and variable cam timing, produces 202 kW (271 hp), 600 N·m (443 lb·ft), and 184 g/km.

The transmission is ZF’s 6HP28, now with an increased torque capacity, uprated hydraulic system with new valve body and a revised torque converter and torsional damper to improve lockup capability.

The XJ also gets a rear differential with increased torque capacity, reduced parasitic losses, and a four-point mounting system to enhance refinement and, for XJ higher performance Supersport derivatives, an active differential control, taking 0.25 s to transfer torque across the axle. Developed in-house by Jaguar, it makes the car more responsive but allows soft bushing rates to be used for refinement, and it should not be confused with ABS/brake-based systems, stressed the company.

Bilstein active damping is also fitted, predicting roll rates based on steering-wheel-sensor inputs. The new XJ gets a fast steering ratio from the Jaguar XFR.

Although in all forms a powerful, high-performance car, Jaguar is stressing the XJ’s environmentally responsible credentials in terms of its aluminum body shell. High-strength aluminum grades add torsional stiffness—to be confirmed but about 20,540 N·m (15,150 lb·ft) per degree—and brings a weight savings of about 40% compared to an equivalent structure in steel. Overall unladen vehicle weight for a diesel model is cut by 15% to 1843 kg (4063 lb) as are CO2 emissions. Jaguar now has 10 years’ experience with aerospace alloy technology.

Riveting stuff

Complementing its use of aluminum are more efficient manufacturing systems and processes, including an 11% reduction in the number of self-piercing rivets compared to the outgoing model, thanks to CAE (computer-aided engineering) optimization.

The use of adhesives (cured in the heat of the painting process) has been reduced by 10%. Steel is used only for hinges and reinforcements; over-molded glass-filled polyamide/ultrahigh-strength steel forms the B-pillar reinforcement. Some composites are incorporated, with GRP (glass-reinforced plastic) molding used to reduce NVH. The car’s front-end carrier is a one-piece magnesium die-casting, and the material is also used for the dashboard crossbeam.

The new XJ’s structure is an extrapolation of that of the previous generation. Some 90% of it comprises aluminum sheet, with castings (used for complex geometry in confined spaces and for high load applications) and higher strength, rivetable extrusions making up, in equal proportions, the remaining 10%.

No welding is used, Jaguar regarding cold forming and joining to be much the preferable solution. The structure includes a high-strength, hydroformed A-pillar/cantrail extrusion assembly to take the Webasto (for all versions) sliding, panoramic roof, which is fitted via an automated system including adhesive application. Extrusions are used for the upper door frames to achieve a slim package along the cantrail to meet design aesthetics criteria.

The new car contains 30-40% structural carryover from the old model but with improvements to help reduce NVH. The regular and long-wheelbase variants were designed together, and there are only about half a dozen parts unique to the latter.

The bodyside of the XJ is one-piece AA6111T4PD material with 1.2-mm (0.047-in) thickness, a reduction of 0.3 mm (0.01 in) vs. the old XJ. Weight and cost savings are each about 20%. It is suitable for all Class-A exterior panels and is compatible with deep-draw press lubricants.

The front door inner section now comprises 10 parts instead of the 14 of the previous-generation XJ. The door is 2.2 kg (4.9 lb) lighter, with a 10% cost saving. Overall parts count for the car shows a 15% reduction.

Detailed weights include 246 kg (542 lb) for body structure, 324 kg (714 lb) for the body plus closures; 26 kg (57 lb) for front doors; 17 kg (37 lb) for hood; and 11 kg (24 lb) for tailgate. Closure parts are produced in-house to cut costs. Roller-hemming is used for all closures.

The car is being produced with a single worldwide body specification.

The car's interior includes the use of virtual instrument displays that, when activated, look remarkably like conventionally designed and manufactured dials, even down to the “chrome” detailing circumference ring. The dials have a driver-attention-getting capability by highlighting the most salient information and prioritizing/reconfiguring for systems warnings such as low windshield-washer fluid.

Like the XF, the XJ gets a rotary gear selector. The company believes that a majority of customers prefer this to a conventional configuration. It frees up space and design options for the interior. The J-gate shifter, used for many years in XJ models and very much in keeping with a sports sedan, has been abandoned, which some may regret. Steering wheel-mounted paddles for manual shifting are standard on all models.

Body building

The XJ is being built at Jaguar’s Castle Bromwich plant. The site's first major use was for the production of World War II Supermarine Spitfire fighters and, later, four-engined Avro Lancaster heavy bombers. It was subsequently used for automotive manufacture.

Extensive improvements have been instituted for manufacture of the new car, including a redeveloped BIW (body-in-white) and trim and final assembly area facilities.

Production is more highly automated, with body assembly robot population upped from 88 to 110. Linked by an ethernet control system, the robots apply structural adhesives and install SPRs (self-piercing rivets).

Jaguar stated that the robotic application of SPRs presented a physical challenge when compared to a spot-welding head at the end of a robot arm. An SPR gun is larger and its cycle time can be slower at about 3 s per rivet, so their use required manufacturing engineering teams to establish a different strategy for the “choreography” of robot movements. The use of simulation tools and a prototype prove-out program were necessary to achieve the necessary efficiencies.

The standard-wheelbase XJ contains 3118 rivets and the LWB 3153. The SPR guns use about 10% of the electricity required for a spot-weld gun and do not need fume extraction or cooling. Decibel levels are lower too.

The underbody construction of the new Jaguar is completed in three stages. Firstly, front floor, main floor, and rear floor are joined as the first major subassembly of the body structure. The bodyside assemblies are then constructed and joined to the underbody on the framing line, followed by front and rear headers and the rear fenders.

Quality checks by laser

Jaguar carries out what it terms “intensive quality checks” during these automated assembly processes and, on completion, 141 laser measurements are automatically performed to check the dimensional precision of each shell. These are subject to real-time statistical analysis.

As at every workstation at Castle Bromwich, if a quality issue occurs, an operator simply presses a button and a member of the plant management team is alerted. A process control board indicates the workstation that has made the alert. The boards also display monitored plant efficiency, again to alert management to any quality issues.

On completion, each BIW is washed at 40°C (104ºF) via an automated system, the structure being cleaned of any dust and residue prior to painting.

Jaguar’s aluminum body assembly has involved close partnerships with several companies, including Steelweld, Kuka, and Laepple providing automation equipment for the bodyshop; Henrob and Tucker, rivet and fastener specialists; SCA, manufacturers of robot-mounted complex sealer dispensing equipment; and Kawasaki and ABB, supplying robots.

The enhancement of lean manufacturing at Jaguar has led to the space required for bodyshop manufacturing to be reduced by some 35%. Extensive virtual modeling was used to design the new XJ assembly facility simultaneously with the engineering of the car.

The XJ’s entire bodyshop layout and equipment existed in a virtual world prior to its installation, including the movement of each robot. The computer tool facilitated the configuration of the outgoing XJ bodyshop to test aluminum assembly processes before start of production of the new car. The use of such techniques has led to a shorter assembly line with fewer workstations.

Pressing matters

Adjacent to the body assembly hall is an aluminum press shop covering 11,366 m² (122,342 ft²). It houses three press lines and 13 presses with a capacity ranging from 400 to 2000 t (440 to 2200 ton). All XJ parts are stamped there as are 30% of those for the Jaguar XF. The shop produces 138 major aluminum stampings for the XJ on two flexible lines having a closed-loop scrap collection system with segregation of alloy type. The Schuler presses are hydraulically driven for maximum control during the press cycle.

A total of 86 diesets (348 dies) are used in the manufacture of the new XJ. More than 20 of these were modified from the previous XJ. They are designed to last eight to 10 years. Supplier partners in this area include Laepple, Kuka, and Ogihara. The shop includes an LK coordinate measuring machine.

Novelis provides the XJ’s aluminum sheet. Working with the company, Jaguar has piloted the use of fusion alloys for future skin panel applications. The alloys used for the XJ include NG5754 for body construction for general forming parts. AA5182 is used for the inner sections of the door panels and other closures; 6111 for exterior body panels and high-strength reinforcements (it is bake-hardenable, increasing strength during the paint shop process). AC170 is used for skin panels for added formability and to reduce panel count, such as for the one-piece trunk lid outer panel. AC300T5, a new high-strength formable alloy was developed for crash/crush applications, having good age-hardening characteristics.

An oil-based lubricant is used for pressings of exterior panels, a wax-based type to achieve reduced friction on more deeply drawn parts, including the intricate floor sections.

Trim and final assembly at Castle Bromwich includes the fully automated panoramic roof glazing cell, where the entire process, including adhesion application, takes 160 s; in-house door and instrument panel assembly; just-in-time sequencing of components to meet individual customer specifications; and powertrain and suspension marriage with the body shell.

The new XJ has been verified by the VCA (Vehicle Certification Agency) as the first Jaguar product to have completed a full life-cycle analysis to demonstrate its environmental impact—including manufacturing and end-of-life phases.

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