Date:31 August 2009
Tweel makes a comeback
Re-imagining the past
Two-stroke engines, like those found in many scramblers, are generally light and powerful. But in many sectors of the power-sport industry, these mighty mites have been replaced by cleaner and more effi cient fourstroke engines. The experimental Lotus Omnivore engine aims to deliver a better two-stroke with a host of new tech. The Lotus concept is still a piston port design, but there’s direct fuel injection and a computercontrolled exhaust valve – it allows precise control of fuel delivery and exhaust recirculation – that should reduce the two-stroke’s tendency to spit out unburned fuel. Most intriguing is the movable puck at the top of the combustion chamber that allows continuous compressionratio adjustments. Lotus says this provides an opportunity for lean mixtures and homogeneous charge compression ignition.
The NuVinci compact continuously variable transmission is poised to migrate from bicycles to cars. The working principle is similar to a planetary gearset; but here, the power flows across a ring of planet balls. Tilting the axis of these balls seamlessly changes the ratio between the input and output cases. Although it can be scaled up for automotive applications to transfer engine torque and doesn’t require power-robbing high-pressure oil like conventional CVTs, we’ll likely first see it running downsized accessories such as alternators. The system could also alter the speed and boost of a supercharger, which would allow an engine to take advantage of high-octane, alcohol-based fuels.
A car’s front bucket seats can weigh more than 20 kg each – especially if they are loaded with luxury features such as heating, cooling and, yes, even massage capability, as in the Mercedes S-Class. And this excess avoirdupois presents a juicy target for weight savings. French auto parts manufacturer Faurecia has developed the Sustainable Comfort Seat, 17 per cent lighter than conventional seats. It doesn’t use foam. Instead, a pair of dimpled, injection-moulded plastic forms cover a nylon and glass fibre frame. It’s about 3 cm thinner than most conventional seats, leaving more room for rear passengers.
Four years after its public unveiling, development continues on Michelin’s airless tyre, the Tweel. During a recent conversation with one of the inventors, Bart Thompson, we learned that the Tweel will fi rst be available for skid steers, ATVs and low-speed Third World cars such as the Tata Nano in as little as 24 months. According to Thompson, “It’s the bottom-of-the-market-type applications, where historically disruptive technologies have transformed industries.” The polyurethane-spoke design remains, but the company is working to reduce high-speed vibration that so far has made it unsuitable for upmarket cars.