Shift of emphasis

Simplified gear technology replaces synchromesh to give drivers the freedom of an automatic with all the benefits of a manual. Siobhan Wagner explains.

An automatic gearbox that allows gears to be changed without torque interruption promises smoother rides and better fuel efficiency in everything from passenger cars to heavy trucks, motorcycles, boats and buses, its developers claim.

The technology, from UK automotive company Zeroshift, works by replacing the synchromesh within a manual transmission with a pair of interlocking rings. These allow the next gear to be pre-engaged while retaining drive in the existing gear. This means that gearshift takes place in zero time and engine torque is not interrupted.

The gearbox gives users the freedom of driving an automatic car with all the benefits of a manual. When comparing vehicles with conventional manual and automatic transmissions, manuals lead to lower fuel consumption and convert more of an engine’s power to moving the vehicle. However, every gear change wastes energy and causes a ‘vrooming’ engine surge that increases fuel emissions.

The Zeroshift gearbox not only has the efficiency of a manual, but also produces instantaneous gear changes, which eliminates the vroom, reduces fuel emissions and wastes less energy.

The company estimates that, in a typical mixed drive cycle, the system should generate a fuel economy saving of at least two per cent compared with a manual transmission, and seven per cent compared with a six-speed planetary automatic.

It also reckons that the reduction of emissions between a Zeroshift automatic and any other kind of automatic is about 10 per cent.

The technology is the brainchild of New Zealand-born mechanical engineer Bill Martin, who founded the company in 2002. His R&D team, which is based in Milton Keynes, is spending the next year perfecting the design of the gearbox so that it is ready for mass production.

His technology has already been demonstrated and proven to industry leaders. According to Martin, he is in discussions with 11 of the 12 largest manufacturers of transmissions by volume.

Zeroshift transmission has been an evolving technology for the last five years. The first test model of the gearbox in 2002 used three metal ‘bullets’ to engage the drive and required manual clutch and shift operation. Later this was replaced with pneumatic gear operation to create a fully-automated gearbox model.

In the version released for commercial use this year, the bullets have been replaced by a pair of interlocking rings, each incorporating three drive elements in a single component and operated by shift forks.

Martin explains the driving elements as ‘drive faces’. ‘On the sides of the gears there are three dogs,’ he said. ‘These are essentially square tube-shaped lugs that come off the side of the gear, and they create a face on either torque direction for driving the power.’

When shifting from neutral, ring one is engaged to take up drive, while ring two is engaged within a few degrees of revolution to take up backlash. The next shift is made with ring two taking up the drive and ring one taking up the backlash. As ring two is unloaded during the change, it requires less than one 20th of the axial force needed by a conventional synchromesh. The control system co-ordinates gearshift actuation, engine management and clutch operation to provide full control over the driveline during gear shifting.

In addition to the innovative drive ring system, Martin said his company recently had another breakthrough —in gear damping to remove the ‘clunk’ sound when gears engage.

Martin’s ambitious timetable for Zeroshift envisages it in production vehicles as early as 2009.

When it does hit the market, he said it will be ready to take on competing technology like the dual clutch. ‘Zeroshift is less expensive to produce, lighter, smaller, more efficient and has lower emissions,’ he claimed. ‘It has stronger acceleration and the shift quality is equal to, or better than, a dual clutch.

‘We are of the opinion that even if somebody is in production with the dual clutch, they are likely to cease and change over to Zeroshift,’ said Martin.