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Baby Jaguar blends technology and tradition

Baby Jaguar blends technology and tradition

What's the fastest growing automotive market segment? Well, according to Jaguar it's the entry-level luxury performance class-that is, small sporty sedans. But up until now, the company did not have a car that could compete directly with the likes of the BMW 3 Series, Audi A4, and Mercedes C Class.

Even during development of its successful S-Type midsize sedan (see DN 7/19/1999, p. 52), the company managers knew they needed a smaller car to remain economically viable in the future. So in June 1997, design began on what is the X-Type that hit world markets this year.

Main man. Once he heard of the company's commitment to build the "small sports saloon" (as it is referred to in the Queen's English), Jaguar engineer Colin Tivey pounded desks, jumping at the chance-which he was given-to lead the program from concept to highway. What followed was what many engineers would consider a dream assignment.

The design team sought to bring about a car that would excel in ride and handling. And, "It had to look like a Jaguar," Tivey adds, but be distinct from other cars the company makes. First off, after the company decided on the size of the car (106.7-inch wheelbase), many elements came together synergistically. Take packaging components for example. "We started with a clean sheet and saw that a transverse mounted engine [crankshaft running perpendicular to the length of the car] would give us the most trunk space," Tivey explains.

The result is a 16 ft3 trunk, larger than the competition Tivey claims, something that Jaguar was not noted for previously. The transverse layout offered the chance to improve driving dynamics with the benefits of all-wheel drive (AWD), especially under reduced traction conditions of rain or snow. To power the car, Jaguar engineers chose the AJ-V6 engine used in the S-Type, in 2.5- and 3.0-liter displacement versions.

A rigid body and stiff mount for the center drive shaft bearing help keep the viscous coupling's output shaft aligned with the rear axle shaft pickup-- cuting mechanical noise-producing hoop stresses along the shaft.

Heavy metal. At around 3,500 lbs, the X-Type is heavy for its size, but, according to Tivey, this results from exceptional torsional stiffness (22,000 Nm/deg; many other sedans are in the mid-teens range) to improve steering, ride, and handling. A specific rigidity benefit is with the rear drive shaft's central bearing, which had to be mounted to a stiff support to ensure keeping the shaft as straight as possible from the transmission into the rear axle pickup point. Such straight shaft alignment avoids rotating, out-of-balance inputs that pump vibrations into the body and suspension. Body stiffness also cuts any tendency for the instrument panel, bolted between the front A pillars, to vibrate and rattle.

Jaguar engineers designed a dual ball-bearing configuration at the top of the front suspension struts (left) to tune out vibrations from the struts into the body and ease steering effort. Previous front and all-wheel drive cars have only a single bearing above the spring (right) or at the top of the entire strut assembly, as in some performance cars.

The AJ-V6 engine has new technology, including a variable geometry three-stage air intake manifold. Opening or closing a combination of two intake tuning valves can optimize the length of the intake system for the engine's speed. A Denso-supplied 32-bit engine management system controls the intake geometry as well as continuously variable intake-valve cam phasing (timing to us Yanks), producing a wide torque band.

Shock treatment. To ensure the smaller X-Type matched the ride and handling Jaguars are noted for, engineers designed a new front-suspension strut upper bearing (see figure). A bearing at the top of the damper (shock) rod and one above the spring decouples engine power effects from the steering by making it easier to turn the steering wheel whether or not engine torque is bowing the strut. "With the older, single-bearing design, the spring and damper loads are along the same path," says Nick Clare, chassis team leader, producing a higher total load. The resulting load requires a stiff material in the top of the mount, which transmits vibration and noise into the body. The dual bearings in the new design, Clare adds, "Provide better isolation-a dual path-where you can tune each aspect by changing the compound and rates-of the damping material above each bearing."

The twin strut bearings are supplied by SKF, with the rod bearing mounted and supplied by ContiTech in a precisely formed damping material fitting. Clare notes, "We originally looked at needle roller bearings as being more compact, but with a slight angular misalignment, you get compression on one side and a gap on the other." Then SKF recommended axial loaded ball races (upper and lower races, rather than inner and outer) for smooth turning operation.

Clutch hit. To distribute engine power under normal traction conditions in a 60/40 split between the rear and front wheels, the designers selected a viscous coupling (VC). While an electronic-clutch coupling could have been used, Tivey explains, "We felt the viscous coupling gave us the best compromise between lateral (steering and handling) and longitudinal (acceleration and deceleration) maneuvers. The major [reason for] using the VC over an electronic clutch device was the compatibility with the ABS and dynamic stability control (DSC) systems." The VC is positioned just aft of the transmission, either a 5 speed automatic or manual gearbox made by Ford.

Gateway modules link the fiber-optic loop D2B data bus (green) to the SCP (blue) body- and CAN engine-control (red) electronic buses.

In the (fiber) loop. The X-Type also incorporates electronics innovations, including the first automotive fiber-optic loop data bus, the D2B Optical Network. Previous fiber applications involved just point-to-point connections. D2B is used for navigation, climate control, audio, TV, and coordination of voice-activated functions. Visible red LED light circles around the system in a 1-mm diameter plastic fiber, which is estimated to save up to 300 distinct wires and their connectors. The light is pulsed at 6 MHz and sent around the loop in a continuous series of data frames by the systems master Head Unit. The frames carry information (three audio channels and one control channel) from one module to any or all the others and are originated at a rate of 44 kHz, the same frequency as CD audio data.

With other data buses, Colin Tivey says it's a case of "horses for courses," with a higher speed CAN (Controller Area Network) bus used for powertrain applications and a lower speed SCP (Standard Corporate Protocol) bus working the body electronics (see figure). Gateway units integrate the bus systems. He says D2B developments underway include Bluetooth, to link future communications features, and minidisk audio.

In summing up X-Type development, Tivey notes the incorporation of new quality processes early in the program, design for manufacturing and robustness, and, even with computerized designs, getting engineers out on the road to test concepts. As to the latter, he highlights the first use at Jaguar of Ford's C3P design tool, a version of I-DEAS from SDRC, to model the car in three dimensions. "We were able to build the car virtually first and see if all the attachments lined up," Tivey goes on. "We could then dial in engine torque and full suspension movement to see if there were any clashes between components."

How did Tivey and his X-Type design team do? Well, some dealers are quoting a six month wait to get one.

A small cat you can love

Suches, GA-"She's a hugger," is how my driving partner describes how the Jaguar X-Type is holding the road as I toss it through the switchbacks on the back roads of northeast Georgia. While steering effort for the small sedan is not excessive, road control is precise. Jaguar engineers have tuned a suspension to the small platform that let's you feel the road while incorporating the traditional Jaguar "float" to smooth out any harshness.
With a 60/40 rear/front power ratio under normal driving conditions, the fact that this car has all-wheel drive is transparent to the driver. At Interstate cruising speeds, most of what little noise there is comes from the tires, with low wind noise and nothing excessive from all the whirling propulsive machinery underneath.

While the 2.5-liter (194-hp, 180-ft-lb) V6 is adequate, the car is a real kick to drive with the 3-liter, (231-hp, 210-ft-lb) version, especially with the manual 5-speed transmission-the first stick available on a Jag in many years. This gearbox is smoother and more precise shifting than the 5-speed on my BMW 528. I felt more decoupled or delayed in controlling the throttle input with the automatic, which just may be my bias against any hint of a time constant in driving!

Nice touches are the standard leather interior and the sport seats with extra bolstering on the sides. Unfortunately, the latter are part of a $2,000 Sport option (17-inch wheels, spoiler, stability control, sport tuned suspension, etc.) that requires the $2,500 Premium option (moonroof, split rear folding seat, power seats, etc.) first. The car itself starts at $29,950-and that for a Jaguar! The sport package also sports nifty British racing green instrument faces, but the instrument needles were rather thin to see with my aging eyes!

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