Ultra-Quick Shift Concepts Challenge DCT
Two new super-fast AMT shift mechanisms presented in recent weeks threaten to challenge dual clutch transmission as the gearbox of choice for ultra high performance super sports cars such as the Bugatti Veyron and Ferrari 458 Italia.
Italian super sports car maker Lamborghini claims that its new ISR transmission can shift ratios in little more than half the time taken by a DCT. Race car transmission maker Xtrac, for its part, has revealed details of its new IGS, or instantaneous gearchange system, that also provides torque interrupt-free shifts at lightning speeds. Developed on the racetrack, IGS is expected to have important road car applications, too, and may even help facilitate the introduction of multi-speed transmissions that shift frequently to minimize CO2 emissions.
Both systems rely for their speed on the near-simultaneous disengagement of one ratio while the new ratio is being engaged. But, though the promised end results may be broadly similar, the two differ fundamentally in the way they approach the challenge of super-fast shifting.
Super-Fast Lamborghini
An all-new V12 engine and the replacement of its mighty Murciélago in 2011 has given Lamborghini the opportunity to develop an innovative robotized gearbox, designed “. . .to guarantee the emotional gearshift that customers expect from a super sports car at the very top of the premier league,”and which it claims is able to shift almost twice as fast as a dual clutch transmission.
While the new powerplant is both lighter (at 235 kg) and, at 700 hp, more powerful than the unit it replaces, it continues Lamborghini’s tradition of large, high-revving V12 engines for its top extreme-performance model. And, as on past models, the unit is placed directly behind the passenger compartment, with the gearbox bolted onto the front and the drive then taken back through the crankcase to the differential and rear wheels. In contrast to most other mid-engined vehicles, where the gearbox is in the free space behind the engine, Lamborghini’s placement of the gearbox effectively between the driver and passenger means packaging is more of a challenge.
The major change comes in the architecture of the gearbox. An automated manual with seven forward speeds, the ISR transmission uses a novel system of independent shifting rods. The two-shaft design places adjacent ratios on opposite shafts; an independent shifting rod is able to disengage one ratio while the next ratio is about to be engaged by a second such rod. By performing these actions simultaneously, rather than sequentially, the high-pressure hydraulic actuators are able to shift gears at a much higher speed – an estimated 40 percent faster than the company’s previous and already fast e-gear system.
A 60-bar electric hydraulic pump and seven valves control the actions of the four independent shifting rods, and the whole transmission assembly weighs 70 kg.
Three driving modes are offered: Strada is for comfort-oriented street driving, including the option of automated shifting. Sport and Corsa are for track use, with the inclusion of Launch Control for maximum acceleration.
Other than stating that shift paddles will be fitted, Lamborghini has not revealed details of the other transmission controls available to the driver. The new flagship super sports Lamborghini using this powertrain will be revealed in 2011 and is expected to be influenced by the Sesto Elemento concept first shown at the Frankfurt IAA in September 2009.
Xtrac’s Instantaneous Gearshift
Best known for its race and rally car transmission systems, Xtrac used the forum of the 2010 CTI Transmissions Symposium in Berlin to present its design for an instantaneous gearchange system (IGS) aimed at road cars as well as competition vehicles.
The IGS is a race car-like automated manual using dog rings and gear-face dogs instead of synchromesh. It achieves seamless, torque interrupt-free gearshifts by engaging the next gear an instant before the current one disengages. This would spell catastrophe on a conventional box but, says Xtrac technical director Adrian Moore, is turned to advantage on the IGS where each gear is fitted with a pawl between the gear and the shaft. The ratcheting effect of the pawl takes care of any overspeeding between gear pairs. As soon as the first gear is disengaged, the pawl on the second ratio re-engages, taking up the drive and enabling the shift to be as near-instantaneous as possible.
The system has been tested in world championship race series with some success, and telemetry tests comparing IGS with a conventional transmission cluster in the same race car show a spike in acceleration (as opposed to a drop) during each upshift. On the track, this corresponds to a speed advantage of 3 km/h over a 450-meter straight.
Moore says IGS has significant advantages over DCT for road vehicles, including lower weight and an architecture that has much more in common with a conventional transmission. With suitable calibration of the engine and transmission, it could be as refined as DCT, too, he notes.
Xtrac is initially producing a two-speed demonstrator concept in an electric vehicle. Moore declined to comment on the clutch arrangements for this concept, but said the race cars used a clutch for initial launch only. Road car applications could help reduce CO2, also, as gearboxes get more gears. “I could see seven, eight or nine ratios, and you wouldn’t be wasting time shifting,” he commented.
Story Filed: 1/26/2011
By Tony Lewin, managing editor DCTfacts.com