“Sport” is a much abused word in the automotive industry. Like “coupe” and “GT” together with other attempts at glorification through categorization, it is open to abuse.
So when Jaguar’s senior engineering executives wanted to demonstrate to Automotive Engineering that its new, mid-size, lightened, aerodynamically efficient, premium 2016MY XF really is a “sports sedan,” they illustrated the point not only on very demanding roads in northern Spain but also on the fast Circuito de Navarra racetrack.
With the supercharged 279-kW (374-hp) 460-N·m (339-lb·ft) 4.0-L V6 engine from the F-type tucked under its hood, the XF was able to show how to convincingly link, at high speed, the words “sedan” and “sport” even with this editor (with no race driver pretensions) in control. It tackled the task with a composed and tidy aplomb.
But the new XF (previously described at http://articles.sae.org/14038/) is also available with Jaguar’s new 2.0-L four-cylinder Ingenium diesel—using Bosch 1800-bar (26.1-ksi) common-rail injection system—with power outputs from 120 to 132 kW (161 to 177 hp), the latter offered in “R-Sport” configuration.
In engineering terms could that, despite its nametag, also be termed a sports sedan? The answer, with one caveat, is in the affirmative.
When Jaguar set out to create the new car, the “must” list of criteria that its engineers had to meet may have seemed daunting, but the result, explained Vehicle Engineering Director Ian Hoban, and Senior Manager Engine Planning and Strategy John Pepperell, is in line with expectations.
Compared to the outgoing XF introduced in 2007, these include a weight loss of up to 190 kg (419 lb) thanks to an aluminum-intensive architecture; torsional stiffness up by 28%; aerodynamic efficiency of 0.26 Cd; improved packaging on a 51 mm (2.0 in) longer wheelbase but 7 mm (0.3 in) shorter overall length; and external and internal design that marks it out as a premium product. The mechanical side includes integral link rear suspension; two- and all-wheel-drive versions; EPAS (electrical power assisted steering); and a very broad engine spread—there is also a 3.0-L V6 diesel with maximum torque of 700 N·m (516 lb·ft).
Of the car’s 3194 part numbers, 2669 are new.
“The new XF shares its fundamental chassis aspects with the XE," said Hoban. "Double wishbones front and aluminum integral link rear suspension we believe are the best combination for handling and premium-level ride comfort.”
Jaguar has accumulated 15 years’ production experience of aluminum throughout its vehicles. “We work at the limit of what is feasible in regard to design and manufacture using the material," said Hoban. "Aluminum skin panels are used for A surfaces, aluminum extrusions for sills, and aluminum castings of varying thicknesses for the foundations of the car such as its front suspension mounts. Technologically challenging aluminum bodysides are single panels, each weighing less than 6 kg.”
High-strength magnesium castings are used for the XF’s front-end carrier and cross-car beam, with ultra-high-strength boron reinforcement, in particular its B-posts for side-impact protection.
Pepperell begins his involvement with all the company’s new powertrains at a very early stage—as he did with those for the XF. That involvement concerns the embryo engineering programs in terms of production and manufacturing strategy.
“It includes technical target setting for the engines in terms of power, torque, refinement, economy, emissions—looking at what technologies there are and what we need,” he explained. “We have a team monitoring the external market place, assessing where we think competitors are going and where we consider we should be positioned. Then we have to translate that into an engineering specification, while considering aspects including complexity as we find the holistic, overall solution.”
That accomplished, Pepperell, who has 27 years’ experience across JLR, and his team hand over to a program delivery team who are responsible for the detailed engineering of the product: “Which for a brand new engine such as the Ingenium will take three to four years.” After that comes the serial development phase.
At Jaguar, another significant element in the development of a new engine is its aural signature, something that must never be subject to palliative action, insisted Pepperell. Much can be done by engineering the exhaust system but he admits that is difficult when developing a small diesel and there is a need for pragmatism: “Frankly, the base diesel will not achieve it.”
Could an active electronic sound system provide a solution; it is something that has been discussed within JLR. If it isn’t authentic it won’t happen, he explained.
Experienced in 132-kW form, the Ingenium diesel, with variable geometry turbocharger (Mitsubishi MHT), does sometimes sound a shade out of place in such a car as the XF, although maximum torque of 430 N·m (317 lb·ft) from 1750 to 2500 rpm helps. It is complemented by a ZF eight-speed auto transmission.
However, one of the XF’s diesel engine options is a V6 diesel. Developed from a Ford/PSA unit, it does make the “right” sound, and with 700 N·m on tap is a very impressive part of the new model’s powertrain repertoire. For the new car, the V6’s performance has been upped from 202 to 221 kW (271 to 296 hp). It gets the XF to 97 km/h (60 mph) in 5.8 s and achieves a fuel consumption of 5.5 L/100 km and 144 g/km CO2 emissions on the European combined cycle.
Ride and handling solutions that provide very high standards for both have been major selling points for most Jaguars for many decades, and the XF achieves that target far more convincingly than its predecessor.
John Darlington, Vehicle Dynamics Engineering Manager, regards the XF’s integral link rear suspension design (developed for the F-Type and also used in the XE) as “our jewel in the crown” with regard to ride/handling.
He also underlines the significance of the XF’s “next-generation” damper technology. For city driving, an additional valve permits some fluid to bypass the main valve in the piston, so reducing the damping force and smoothing the ride. As vehicle speed builds away from the city, the valve closes, forcing all of the fluid to pass through the piston to firm the ride.
On V6 versions of XF, a configurable dynamics system (tailored throttle mapping, transmission shift strategy, steering feel, and adaptive dynamics settings) is fitted and controlled via a touchscreen menu.
All of this is part of Jaguar’s determined aim to create a car that can carry convincingly the appellation: sports sedan.Continue reading »