Stop/start for Jag V6 oiler?

Jaguar's new diesel V6 is an example of creative engineering in its own right, but it also hints at the way forward for diesel technology. That said, there are some limitations on how far and how wide the technology can be employed.

Initially available in the Jaguar XF, the new engine matches the NVH standards of a petrol V6 and the throttle response and output of a petrol V8. It's an impressive unit that relies on sophisticated control systems and lateral thinking to achieve this result.

The man overseeing the development of the XF -- and its diesel V6 variant -- is Jaguar's Chief Program Engineer, Kevin Stride. Stride, out here for the local launch of the upgraded XF (more here), has been employed by Jaguar since 1987 -- two years before Ford picked up the company.

His passion for the prestige brand reaches back as far as the age of seven, when he informed his parents that he was going to work for Jaguar one day. His aspirations -- influenced by an XK120, an E-Type and an early XJ12 owned by the father of a friend -- came to fruition when Stride commenced working with Jaguar as an engineering cadet, spending six months of the year studying and six months working.

The Carsales Network spoke briefly with him after the launch and asked what provided the inspiration for the radically different way of handling forced induction for the new 3.0-litre diesel.

"The original inspiration came from our diesel engines group -- at Whitley in Coventry -- working with Honeywell [Garrett, the turbocharger supplier] and PSA [Peugeot Citroen] to deliver this system…" answered Stride. "I think it's fair to say that the whole inspiration and concept came from our own engineers."

The engineers were possibly guided by Jaguar's own market research, which determined that drivers demand high torque below 2000rpm 80 per cent of the time and below 4000rpm in 95 per cent of all cases. In other words, modern drivers usually don't want or need the sort of high-revving output from engines powering cars they drive day-to-day. Both the diesel and the two petrol V8s -- including the supercharged V8 in the XFR -- have been developed with these needs in mind.

Given the involvement of PSA Peugeot Citroen in the development of the 3.0-litre diesel -- the company also co-developed the original 2.7-litre twin-turbo V6 diesel -- will we see the new engine powering cars developed by the two brands as well as Jaguar and Land Rover?

"No, I don't think you will, personally," Stride responds. "Two things to consider: As far as we know, we believe the set-up on that base engine is unique to us; the second thing is... if you think about the types of products that Peugeot Citroen... would want to put that into, [they] typically would be front-wheel drive. The reason that you do the turbocharging system that we've gone for is very high levels of torque and very fast delivery -- which is probably not something you'd want to do in a front-wheel drive car."

The new diesel induction system features a 'crossover' pipe to channel exhaust gases from one bank of cylinders across the V formation of the engine to the other side, where it merges with the exhaust gases from the other bank, to feed the 'primary' turbocharger.

This is a large turbine which, through use of variable nozzle geometry, can spool up with minimal lag. Unlike other diesel engines, the large turbine works at low speeds, and the smaller 'secondary' turbocharger only operates at higher revs and under higher loads. In conventional sequential turbocharging systems, it's the larger turbo that operates at higher revs, when there's already enough exhaust gas pumping through the engine to overcome the inertia of the heavier mass. The smaller turbo works at lower speeds, where lighter mass provides faster throttle response and reduced lag.

In the Jaguar set-up, control systems modulate the charge and the primary turbo's operation to skirt around the issue of turbo lag. When the secondary turbo joins the party, the primary turbo continues to operate, with the smaller turbo providing supplemental boost. The way the system operates, charge from the smaller turbo is gradually phased in. At slower engine speeds, a control valve ensures that no exhaust gases reach the secondary turbo. As the engine approaches the point where the secondary turbo needs to assist, the exhaust gases are diverted to the smaller turbo, but the charge from the secondary turbine doesn't reach the engine's combustion chambers until it can be introduced seamlessly.

According to Stride, it's the first time such a system has been used in a V-configuration engine.

Since the 3.0-litre diesel's forte is the ability to deliver high levels of torque on instant demand, it doesn't appear to be a natural candidate for an auto-stop/start system. Yet it's hard to imagine that such a recent development as this engine would have been formed in a vacuum and without the guiding principle in mind that it should lend itself to such a fuel-saving device.

"We wouldn't be able to confirm what we're doing on that [feature]," says Stride, who believes that the development of auto-stop/start -- for petrol or diesel engines -- is dependent on market demand. It's also dependent on finding a window of opportunity in an engineering schedule to introduce the development of this feature, perhaps in a micro-hybrid package with regenerative braking. Stride insinuates that hasty development of micro-hybrid technology -- without tailoring the drivetrain to suit -- could ultimately impact on the brand's improving reputation for build quality and reliability.

"Typically, you'd have to consider where [a project] is in its engineering life; ie: are we doing any other specific engineering actions which would allow us to bolt it on easier, because the system control is pretty complex for any stop/start system. You can't just do a six-month exercise to go and stick it in something that's already there -- and expect to do a good job.

"You could probably 'knife and fork' it in, but... it's been a long, hard road to set the standards where we've got to now -- and we're not going to step on that now."

The engineer agrees with the traditional view that allying the fuel-saving device to a diesel engine remains a challenging task -- "It's a current view, and it's a very accurate one," he says. Sister company Land Rover is shortly to introduce stop/start technology in the Freelander 2. However, the Freelander uses a manual transmission. For Jaguar, its dependence on automatic transmissions in its cars complicates the issue. 

"The next big challenge," Stride adds, "is to do a very refined micro-hybrid type of technology with a diesel automatic -- in the industry, we're not saying for Jaguar Land Rover.

"For a stop/start system, doing it for an automatic diesel is probably the hardest challenge out there, but if we choose to go down that route -- and we've got several options we're looking at -- I think we know how to do it."

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