Are you as clever as your tyres?
On the surface, tyres are not very exciting, but when you delve into the technology behind the modern tyre it becomes clear that research in this field can be very exciting. Most tyre companies are trying to improve run-flat tyres but, despite the undoubted safety margin they offer over a normal tyre in the event of sudden deflation, many feel that they are not necessarily the answer for the South African market. Our towns are in many cases too far apart, and the feedback we get from readers is that run-flats are not worth the trouble. But other developments look very promising…
SENSING TYRES
The automotive engineering laboratory at Helsinki University has perfected an optical tyre sensor that measures the friction potential between the tyre and the road. The information from a sensor in the tyre, which measures lateral force via carcass movements, is combined with existing vehicle dynamics and temperature sensors to enable a processor to estimate the friction between the tyre and the road before the ABS or the ESP comes into action, not after these driver aids have kicked-in.
The system works so well that it is even able to sense the onset of aquaplaning and warn the electronic systems (and the driver) that full aquaplaning is taking place, in spite of the fact that there is no contact between the tyre and the road when this happens. Currently the system is expensive, but it will be a useful tool for tyre manufacturers. Eventually it may reach the luxury car market.
Ari Tuononen, who leads the above research, is convinced that more accurate on-board measurement of tyre deflection will enable the control unit to estimate lateral, vertical and longitudinal forces between the tyre and the road. This will make existing ESP control systems more efficient because it will enable the grip at each wheel to be utilised fully at any stage of the cornering process. Tuononen’s laboratory is also working on tyre load-sensing devices mounted in the tyre or on the suspension units, but he estimates that it will be many years before such systems will be production-ready.
PIRELLI CYBER
In similar vein, Pirelli plans to introduce an intelligent tyre – one that has a memory – next year. Although not as sophisticated as the Helsinki system, the Pirelli set-up does represent a step in the right direction. It is called the Cyber tyre, and is fitted with a multi-purpose sensor, plus electronics and a power source.
These components are glued to the tyre wall and wirelessly relay information such as tyre acceleration, contact patch size, road surface conditions and load on the tyre to the ABS/ESP units.
How does it work, and how accurate is it? Pirelli is keeping mum, but it sounds very exciting.
SELF-INFLATOR
Coda Developments, a parts supplier from the Czech republic, recently received an international tyre technology award for innovation and excellence for its self-inflating tyre (SIT). It should be in production by next year and utilises a peristaltic pump that employs the vehicle’s weight and motion to inflate the tyre as needed. Peristaltic motion is the rhythmical contraction of the walls of a tube, affecting each section in turn, like a Mexican wave. This is how the human oesophagus gets food to go down.
The inflation system has only two components; a tube chamber functioning as a peristaltic pump, and a pressure management device to control the inflation. Coda’s Frantisek Hrabal explains: “The peristaltic tubing is located longitudinally between the rim and the tyre wall, and follows almost the whole perimeter of the rim.
Normal tyre deformation caused by the weight of the vehicle creates a closure of the tubing at its lowest point. As the tyre moves against the road this closure pushes the air contained inside the tubing into the tyre and simultaneously pulls air on the outside back into the tubing. As a result, the tyre is inflated with the contents of the tubing with each wheel revolution until it reaches a desired pressure.”
This system has to be controlled to stop when the desired pressure is reached, and it is able to cooperate with a pressure monitoring unit so that it not only warns about a loss of pressure, but also starts to pump up a tyre that is losing pressure.
PRESSURE MONITORING
Compulsory tyre pressure monitoring systems (TPMS) are just around the corner for most countries. They are already mandatory in the USA, and Europe will follow soon. Most tyre pressure monitoring systems are indirect, ie they rely on the wheel speed sensors to detect a change in speed, with the result that most are only able to detect pressure drops of more than 20 to 25 per cent. Direct systems are coming into use; they’re more sophisticated and in some designs can even give the actual pressures. Most of these systems utilise sensors mounted in the wheel, but tyre-mounted units are becoming available.
EASTERN INNOVATORS
When it comes to innovation, major tyre companies are facing a lot of competition from smaller concerns and it’s especially noteworthy that Korean manufacturers are expanding at an astonishing rate. Both Kumho and Hankook are in the top ten as far as sales are concerned and they both have research institutes in Akron, USA, known as the rubber capital of the world.
Kumho recently revealed some experimental tyres that show a lot of promise. It is the only tyre company with a qualified vehicle designer on its payroll to explore future vehicle technologies.
He is ex-Fiat stylist Rob Dalton and is based at Kumho’s European Technical Centre in Birmingham, England. Dalton was asked to design three sets of dream tyres and responded with three concept vehicles that run on his ideas. The cars are called Pulse, Epoch and Fortis.
The Pulse name comes from a tyre design that uses the physical properties of the tyre to act as a sensor. Tiny piezo-electric units in the tyre generate an electrical current that is registered by sensors as deviations from established norms.
A radio transmitter sends the sensor output to a facia-mounted monitoring system that can detect changes in tyre pressure and heat flow. A dangerous build-up of stress can then be inferred from the data to warn the driver of impending failure.
The Epoch is inspired by Kumho’s success at Le Mans in recent times. The vehicle’s frame is built up from bamboo, giving an immediate carbon-offset, and the body panels are formed from recycled tread rubber.
Power comes from Maglev units in the four wheel hubs, but quite how they work has not been revealed. The tyres feature electro- active polymer (EAP) technology that allows the tread and even the shape to be altered by passing an electric current through the rubber. By this means the characteristics of the tyre can be changed at will, to tie-in with driving conditions and the driver’s preference.
The Fortis design study is electrically powered and aims to solve the dilemma that currently confronts the buyer of an offroad vehicle: he either has to decide at purchase what tyres suit his intended use of the vehicle (if he’s given a choice at all) or else he has to own at least two different sets of tyres. Most off-road vehicles are fitted with tyres that are not suitable for any serious deviations from a hard and smooth surface.
The Fortis allows the driver to select the tread pattern on the move by changing the inflation level. The tread design features projections – called biters – that are raised to improve off-road grip when the pressure is lowered, and covered to allow smooth and quiet progress when the pressure is increased.
AIRLESS TYRE
Michelin showed an airless tyre, called the Tweel, to the media a few years ago. In this design, a wheel hub is connected to an outer rim by means of flexible polyurethane spokes that absorb the road shocks in the same way that a normal sidewall does. The outer rim contains a conventional moulded tread and a shear band just below the tread that creates a compliant contact patch.
The design of the spokes can be varied to change the tyre characteristics. The rolling resistance and mass of the prototype differed by not more than five per cent from the values obtainable on conventional tires, but the lateral stiffness was five times higher, thus promising exceptional steering response. The major disadvantages at this stage of development seem to be excessive vibration, heat and noise.
Note: Some of the information and illustrations in this article are from the publication Tire Technology International.
