Non-pneumatic tires (NPT), or Airless tires,
are tires that are not supported by air pressure. They are used on some small vehicles such asriding lawn mowers and motorized golf carts. They are also used on heavy equipment such as backhoes, which are required to operate on sites such as building demolition, where tire puncture is likely. Tires composed of closed-cell polyurethane foam are also made for bicycles and wheelchairs. The main advantage of airless tires is that they cannot go flat, but they are far less common than air filled tires.
Airless tires generally have higher rolling friction and provide much less suspension than similarly shaped and sized pneumatic tires. Other problems for airless tires include dissipating the heat buildup that occurs when they are driven. Airless tires are often filled with compressedpolymers (plastic), rather than air.
Michelin is currently developing an integrated tire and wheel combination, the “Tweel“, that operates entirely without air. Automotive engineering group of mechanical engineering department at Clemson University is developing a low energy loss airless tire with Michelin through the NIST ATP project.
Resilient Technologies and the University of Wisconsin–Madison’s Polymer Engineering Center are creating a “non-pneumatic tire”, which is basically a round polymeric honeycomb wrapped with a thick, black tread. The initial version of the tire is for the Humvee and is expected to be available in 2011.
TOKYO MOTOR SHOW-2011
This week at the Tokyo Auto Show in Japan, Bridgestone showed off its latest development – puncture-less air-free tires. The tires are still in the concept phase, but have been successfully tested on single-person vehicles in Japan traditionally used for elderly people.
The 9-inch wheels have thermoplastic-resin spokes that radiate from the rim to the tread, curving to the left and right for maximum structural support. The tires’ solid design doesn’t require air, and consequently can’t be punctured – so, no more flat tires.
Also interesting is the material the tires are made of, which is entirely recyclable.
Still in the testing phase, Bridgestone plans to heavily evaluate the tires’ performance on traditional cars before making them available to the general pubic.
While certainly interesting, Bridgestone’s tires aren’t the first we’ve heard of to go air-free. Airless tire technology has been under investigation for years, with Michelin’s airless Tweel tires even winning the Intermat Gold Medal for Innovation in 2006.
April 29, 2005 Michelin has showcased a potentially disruptive technology with significant ramifications for the future for mobility: an airless, integrated tyre and wheel combination dubbed the TWEEL (i.e. Tyre/WhEEL) . The Tweel promises performance levels beyond those possible with conventional pneumatic technology. The first commercial applications of the Tweel will be in lower-speed, lower-weight vehicles such as the iBOT mobility device and Segway’s Concept Centaur. Designed by Segway-inventor Dean Kamen, the iBOT mobility device has the ability to climb stairs and navigate uneven terrain, offering mobility freedom impossible with traditional wheelchairs. Additionally, Segway’s Concept Centaur, a prototype that applies self-balancing technology to a four-wheel device, has also been equipped with Tweel to increase its performance potential.
Benefits of the Tweel
The heart of Tweel innovation is its deceptively simple looking hub and spoke design that replaces the need for air pressure while delivering performance previously only available from pneumatic tires.
The flexible spokes are fused with a flexible wheel that deforms to absorb shock and rebound with ease. Without the air needed by conventional tires, Tweel still delivers pneumatic-like performance in weight-carrying capacity, ride comfort, and the ability to “envelope” road hazards.
Michelin has also found that it can tune Tweel performances independently of each other, which is a significant change from conventional tires. This means that vertical stiffness (which primarily affects ride comfort) and lateral stiffness (which affects handling and cornering) can both be optimised, pushing the performance envelope in these applications and enabling new performances not possible for current inflated tires.
The Tweel prototype, demonstrated on the Audi A4, is within five percent of the rolling resistance and mass levels of current pneumatic tires. That translates to within one percent of the fuel economy of the OE fitment.
Additionally, Michelin has increased the lateral stiffness by a factor of five, making the prototype unusually responsive in its handling.
Source: Tech-on
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