Currently reading: 50g/km Jaguar XJ driven
Autocar drives the Jaguar XJ Limo Green, which has average CO2 emissions of 50g/km

Think the future looks bleak for big executive saloons? Steve Cropley did too – until he tried Jaguar’s taken on a greener, leaner XJ.

The concept

It is obvious that all cars must become dramatically more frugal and emit far less CO2 in future. New moves are showing that the luxury saloon can last.

In fact, there are signs that it can have an extremely bright future – if it adopts the latest plug-in hybrid technology demonstrated by Jaguar’s new ‘Limo-Green’ saloon, the result of a £4.2 million project to build an ultra-clean big car.

The first prototype, exclusively driven by Autocar last week, is the first fruit of a two-year programme run by a consortium comprising Lotus Engineering, the MIRA research organisation and Caparo, the giant components supply group, and is part-funded by the government’s Technology Strategy Board.

The first Limo-Green prototype – one of an eventual three – is already getting close to targets set for top speed (112mph), has beaten targets for acceleration (0-60mph in 8.0sec) and is demonstrating a range of close to 30 miles in electric-only mode. It can also easily exceed an initial CO2 emissions target of 120g/km – with a real-world figure closer to 50g/km.

Limo-Green’s powertrain consists of a home-charged 360-volt lithium ion battery bank – weighing 93kg and housed in the spare wheel well – feeding a 200hp brushless DC electric drive motor with two-speed gearbox, located down where the original ZF automatic used to be and driving the rear wheels.

There’s a featherweight 60bhp, 1.2-litre, lean-burn, three-cylinder Lotus engine mounted back to front in the nose, configured by clever electronics to start automatically and drive an on-board generator when the battery bank needs more charge, as it will on any journey greater than about 30 miles.

However, because the consortium’s research indicates that anything up to 80 per cent of an average XJ owner’s journeys fall well within EV range, hence the estimated 50g/km CO2 output (not including power station emissions) in real-world use, although the figure is 120g/km when the engine is running.

The test drive

We came away deeply impressed from our drive in the prototype, not because the performance was different from a normal petrol or diesel-powered XJ, but because it was so very similar.

This prototype, more frugal than a Ford Fiesta and with a touring range of well over 600 miles, could be driven in just the same way as any conventional XJ. It had the same strong acceleration (0-62mph in 7.5sec) and the same easy-rolling cruise for which Jaguars are famous.

It feels powerful, because electric motors develop full torque from standstill. The ‘throttle’ pedal is a little more sluggish than in a standard XJ, but Limo-Green engineers have made it so; a car like this gets driven by dozens of people, including heavy-footed politicians, without much in the way of mechanical sympathy. The drive is exceptionally smooth and if you want to go faster you just press harder.

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Sure, it had a few jerks and rattles, and its top speed was restricted to around 90mph by the transmission’s two gears, but it was instantly clear that the next two prototypes, nearing completion at MIRA, will banish most of these glitches. Jaguar’s plan is to have around 100 Limo-Green prototypes running globally by 2012.

What’s next?

Limo-Green project boss Steve Nicholls points out the essential versatility and simplicity of his car’s layout. “This is a pure electric vehicle,” he says. “The electric motor is its only form of propulsion. The petrol engine’s function is to drive the generator. It is carefully specified to be small enough to be efficient, but big enough to keep you going.

“The generator, which works as a starter for the engine, switches polarity as the car stops to provide regenerative braking and recover some battery charge in the process.

“As time goes on, the engine could potentially be replaced by a diesel, an engine running on CNG, a gas turbine, a fuel cell or whatever makes sense for the future.”

The verdict

The project appears to demonstrate that lighter, quieter and much more frugal XJs are coming to tomorrow’s showrooms. Which means the major happiness is coming to the big Jaguar owners of the future.


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Straight Six Man 9 June 2010

Re: 50g/km Jaguar XJ driven

MrTrilby wrote:
Straight Six Man wrote:
Frankly, it's a rather half-arsed effort compared to some of the other things under development.
Like what? It sounds rather comparable to the Volt/Ampera, and I mean that in a good way.

The Volt/Ampera has hub motors, thus doing away with the diff. The US turbine supercar has hub motors and a turbine (so it's vastly more efficient than this Jag). Jag themselves are developing a turbine-and-hub-motors version of the Limo Green (what a naff name!). Just plain XJet, or XJ-T, please, Jag... and make it a turbine. Alternatively, XJ-E, E for Economy, Eco credentials and Efficiency, if it's got an IC engine...

The problem with the hub motor idea is unsprung weight. However, it does also do away with the very significant frictional losses of the differential and transmission. Anyway, as I understand it, modern series hybrids with hub motors have the motors actually a bit inboard of the hub, fixed to the floorpan of the car, th some sort of universal, ball or constant velocity joint between the motors and the wheels, so the motors actually are no longer unsprung. This aids the ride and handling.

Of course, even the very best internal combustion engines are fatally flawed: there are huge reciprocating masses, and a heck of a lot of friction. They're just not that efficient. This is why the aerospace industry moved away from the internal combustion engine towards the turbine for a hell of a lot of applications... instant torque, smoothness, simplicity, reliability.

gathome 8 June 2010

Re: 50g/km Jaguar XJ driven

CambsBill wrote:
According to AutoExpress "The arrangement is similar to the system in Vauxhall’s Ampera – but in the Jaguar, the 1.2-litre engine provides power directly to the rear wheels. In the Ampera, the unit only charges the battery." So who is correct? The Autocar article implies it's the same set up as the Ampera (engine only charges the battery) but AE suggest otherwise.

I'm with Cambsbill on this matter; I only have the information provided in the articles, but there are two reasons to belive the Autocar version.

Firstly the picture in Autocar shows a layout with the small engine separated from the gearbox and propshaft by the electric motor. It suggests visually an electric drive with the ic engine there to power the generator.

Secondly, by using an optimal set up with the petrol engine being used to drive only a genrator it can be "tuned to operate at peak efficiency, not needing to cope with running over a wide rev range. This can simplify engine management needs and avoid running at inefficient speeds.

An earlier post commented on a crude electric motor >gearbox >propshaft > diff > driveshaft > wheel arrangement; preferring the use of hub motors. Quite elegant, but my concern would be over high unsprung weight, an enemy of ride and handling.

Another post mentioned that the power of the little Lotus engine would limit performance. In some ways it could, but given a large poweful engine, in real world driving conditions how often is it actually going to be rquired to run at peak power for long periods. The ability to maintain a sustained high speed cruise is frequently restricted by driving conditions. The article suggests a 120 mph max. The Lotus engine can run at peak charging level when needed, Performance is limited by the charge in the battery. If the battery holds charge the performance is available. So over an average journey at times the charge will be building, because the engine provides more than is needed, at other times it will be depleted.

My feelings are that this is the right approach. Electric drive, with a battery storage capacity and an ic engine to generate power en route. By using the ic engine only as a generator it can gain efficiency benefits by operating at best speed, and a smaller lighter engine is needed which brings benefits in all areas. The best fuel for the small engine is a matter for further consideration.

CambsBill 8 June 2010

Re: 50g/km Jaguar XJ driven

smarttony wrote:
According to AutoExpress "The arrangement is similar to the system in Vauxhall’s Ampera – but in the Jaguar, the 1.2-litre engine provides power directly to the rear wheels. In the Ampera, the unit only charges the battery." So who is correct? The Autocar article implies it's the same set up as the Ampera (engine only charges the battery) but AE suggest otherwise.

Auto Express are wrong. The engine is designed to run at a constant speed, optimised for economy/charging.