Smooth Operators
New Models from BMW, Audi and Jaguar Demonstrate the Latest
Planetary Automatic Technologies
Much discussed by engineers for the last few years, ZF’s innovative, eight- speed planetary automatic transmission is now out in the market, equipping the Rolls-Royce Ghost and certain models within BMW’s 7 series, 5 series, and 5 series Gran Turismo ranges.
Arch-rival carmaker Volkswagen Audi has also made the move to eight speeds. Its top Touareg and Q7 SUVs, along with the Porsche Cayenne built on the same platform, use a new eight-speed automatic from Japanese supplier Aisin. However, for its new flagship model Audi is shopping closer to home. The A8 quattro sedan also uses the ZF 8HP, this time with four-wheel drive power distribution via an angled side shaft running forward from the tail of the gearbox.
Jaguar, meanwhile, has
chosen ZF’s second-generation six-speeder for its new, top-premium XJ sedan.
Jaguar engineers can be expected to incorporate the eight-speed with minimum
delay, once it becomes available. This could be sooner than many expected, as
the new eight-speed has just been announced on sister brand Land Rover’s latest
flagship Range Rover. In the meantime, however, a trip in the new XJ shows that
this installation of the six-speed is so good that it is hard to believe that
the eight-speed can possibly offer any improvement.
With over 500 hp ready to be unleashed from its supercharged V8 gasoline engine, the Jaguar’s gas pedal has to be treated with delicacy. At low speeds, it is impeccably smooth in Drive – selected using the very classy rotary knob that rises from the transmission tunnel when the engine is started. In Sport or Performance mode, though, it needs more caution if you want to avoid going much faster than intended.
While the Sport setting on the rotary selector brings quicker throttle response, more clearly perceptible gearchanges and a more pronounced rumble to the big V8, pressing the checkered-flag button behind the selector brings in all the sports systems, including those for the chassis and steering. To add to the effect, the background on the futuristic, solid-state instrument pack turns a racy red. In this mode the XJ is searingly powerful, with an angry bark from the exhausts and an instant kick in the back whatever the speed and whatever the gear – not that the driver is often aware of which gear is in use until he or she operates the steering wheel-mounted paddles.
Conventionally configured with upshift to the right and downshift to the left, these provide almost race car-like control over the drivetrain, transforming the big limousine into a formidable machine for fast, open roads – and even tighter terrain, too.
Part of the appeal of the Jaguar is that, despite its external size, it has an excellent driving position and a neat, intimate driver cockpit that is not as intimidating as those on most top luxury models. The Audi A8, perhaps by coincidence, generates a very similar feeling from the driver’s seat, also boasting a small steering wheel, a low top to the dashboard, and a neat, L-shaped gear selector on the tunnel just in front of the engine start button. The lever is a model of simplicity, with just P, R, N and D positions. Once in Drive, a slight press rearward on the lever is enough to select Sport; a repeat press brings the system back into Drive. The rest is handled with surprising ease via the Audi Drive Select function in the A8’s MMI interface. This offers the choice of comfort, auto, dynamic, or personal, each a collection of settings for the complete vehicle.
Dynamic, for instance, makes the suspension very firm and the steering firm to the point of heaviness, and puts the transmission straight into Sport, when its responses are faster and less blurred.
The 4.2 liter V8 diesel is a remarkable engine – very smooth, immensely torquey, and quiet, but with a hard-to-define, odd quality to its sound. The eight-speed ZF 8HP does an excellent job in coping with the huge shove that this engine provides. At high speed, for instance, it will kick down from eighth into fourth quickly and with relative smoothness – something a DCT would struggle to do. In Comfort mode, when the suspension is American-style soft, the transmission is able to make the most of the diesel’s great torque and settles into a high ratio at the first opportunity.
The ZF 8HP in the BMW 535i driven here must be one of the most eagerly awaited combinations the auto industry has ever seen. It has certainly been worth the wait, as this is one of the most impressive automatic applications ever seen on a premium car. It gives credence to the confidence shown by German automakers in the future of planetary transmissions for a combination of comfort, performance, and economy.
Comfort is especially well-handled on the BMW, with its potent but also torquey, 3 liter straight six. Thanks to twin small turbochargers which spin up quickly at low engine speeds, the 535i has very good low-down torque for a gasoline engine – and the automatic makes the most of this. Upshifts are so smooth as to be imperceptible; even under hard acceleration they are pleasantly blurred. Kickdown, likewise, is rapid, even across several ratios, and the gap is never big enough to cause a jolt.
For performance driving the 535i powertrain is equally rewarding, thanks in no small measure to the control systems installed by BMW. Alongside the gear selector lever is a rocker switch allowing the driver to increase the firmness and responsiveness of the whole vehicle, including the engine and the gearbox, in four steps from Comfort to Sport Plus. In all but the latter, the drivability of the 535i remains excellent. The top two settings are rewarded by much sharper engine mapping, snappier upshifts, and useful engine braking for bends when using the wheel-mounted shift paddles.
Yet, the transmission can play the opposite end of the scale with equal confidence, easing along at a relaxed pace with perfect smoothness. All in all, the highly accomplished 8HP is a tough target for a rival technology such as DCT to aim at, especially in a luxury car environment such as the BMW 535i where it can show the full breadth of its talents.
|
Jaguar XJ 5.0
V8 Supersport |
Audi A8 4.2 TDi Quattro |
BMW 535i SE | |
|---|---|---|---|
| Engine | 5.0 V8 gasoline, supercharged | 4.2 V8 turbo diesel | 3.0 liter gasoline six, twin turbo |
| Max Power | 510 hp | 346 hp | 306 hp |
| Peak Power | 625 | 800 Nm | 400 Nm |
| Transmission | Six-speed ZF 6HP gen 2 | Eight-speed ZF 8HP | Eight-speed ZF 8HP |
| 0-100 km/h Acceleration | 4.9 sec | 5.5 sec | 6.0 sec |
| Max Speed | 250 km/h | 250 km/h | 250 km/h |
| Fuel Consumption |
12.1 l/100 km 18.7 U.S. mpg |
7.56 l/100 km 29.9 U.S. mpg |
8.41 l/100 km 26.9 U.S. mpg |
| CO2 Emissions | 289 g/km | 199 g/km | 199 g/km |
| Price (UK) | £88,000 | £63,900 | £37,300 |
| Price (U.S.) | $127,000 | $92,600 | $54,000 |
Story Filed: 7/7/2010
By Tony Lewin, managing editor DCTfacts.comdiv