For over 100 years tyres have been a fit-and-forget item. Sure, you're supposed to check pressures and condition weekly, but for the vast majority of drivers, attention is only given to the black doughnuts when all the tread is gone and it's time to make a decision about what brand and model of tyre should be used as the upgrade.
But tyres are set to change massively in the next five years. No, not in shape and construction, but in the way that they are monitored. One of the major incentives for this change is recently introduced US legislation requiring that beginning with the 2004 model year, all new vehicles are to be fitted with a system that alerts the driver to low air pressure in one or more of the tyres. So all OE manufacturers which sell cars in the US are developing systems - with some already being released in new cars. In addition, the aftermarket is also responding, with a number of tyre pressure monitoring systems now available for retro-fitment.
But that's not all. Development is also under way of tyres that will have micro-chips actually integrated into the tyre's construction, allowing the sensing of data in addition to pressure - factors such as the number of rotations that the tyre has undergone and its peak temperatures. Even more incredibly, one company has just patented an approach that makes the whole tyre a sensor, with a quite unbelievable amount of real-time data able to be gathered from it.
So stand by for the electronics revolution - the one that has already made its presence felt in the rest of the car - having an impact on tyres.
Chips in Tyres
While the widespread introduction of tyre pressure monitoring almost universally uses add-on sensors placed inside the wheel or air valve, the integration of electronics into the tyre carcass itself is also being explored. In conjunction with tyre manufacturer Continental, German automotive electronics supplier Siemens is developing a process that places sensors within the tyre rubber. The aim is to use the sensors to pick up tyre pressure, temperature and road surface adhesion while the tyre is actually rolling. This will aid information input into driver information systems and control systems for the drivetrain, such as stability control systems.
The tyre tread sensor contains a surface wave device that does not require any additional energy source (eg a battery) in the tyre. A high frequency module transmits electromagnetic waves to the surface wave sensor at a frequency of 433MHz. These signals, which are converted into acoustic surface waves, spread out along the surface of the sensor. At defined points, the acoustic waves are reflected and converted back into electromagnetic waves. Again reception is via a high frequency device.
Variations in the spreading time of the waves create a phase delay between transmission and reception signal. The cycle of the acoustic wave depends on the mechanical load on the surface wave sensor - bending or tensile load will cause a change in the phase delay, enabling information to be sensed relating to flexing in the tread and the tyre adhesion coefficient.
Taking this approach allows the sensor complete freedom from a power supply or the need for internal batteries. The latter is a problem not only in the difficulty of replacing them(!), but also in that a battery supply would make the sensor both larger and heavier, causing problems in terms of tyre balance and durability.
Using sensors such as these to measure the real-time tyre adhesion coefficient offers substantial benefits:
- The control of ESP (Electronic Stability Control) and ABS can be specifically selected before brake pressure builds up.
- Braking of individual wheels can be improved.
- Early identification of aquaplaning is possible.
- The tyre adhesion coefficient can be used as an input to the Adaptive Cruise Control (ACC) - adjusting the safety distance to the vehicle in front will be possible.
Changes in tyre pressure can also be detected and so the use of this passive system means rolling resistance can be minimised by maintaining optimum tyre pressure, so increasing the service life of the tyre. Early identification of a drop in pressure can also prevent tyre failure and a potential accident.
These sensor systems do, however, also have a drawback - more complex production will mean higher tyre costs.
At the moment the in-situ tyre sensors are still at the laboratory stage, although Siemens sensors have already been vulcanised into standard tyres produced at Continental and measured in different rolling situations on a drum testing machine at Darmstadt Technical University. In that testing, they successfully withstood extreme conditions. A number of parameters were varied, including tyre pressure and axle load, and an analysis of the signals showed that the surface wave sensors supplied reproducible and useful information directly from the tyre tread.
There are, however, no plans to go into volume production with the tyre tread sensor before the year 2006.
Another technology has just been patented by Japanese tyre maker, Bridgestone. US Patent 6,257,289 (assigned July 10, 2001) describes a sensor that is buried in a projected portion of the inner surface of the tyre bead. Primarily designed for use in heavy industry tyres, the sensor is a cylindrical-shaped device manufactured from a glass envelope covered in a shock-resisting synthetic resin.
In this diagram (7) is the sensor, (9) is the integrated circuit comprising the main element of the sensor, (10) is the antenna, (11) is the 0.3-2mm thick glass envelope, and (12) is the 0.5-3mm thick synthetic resin layer.
It's intended that the sensor not be monitored continuously from within the cabin of the vehicle, but by an operator equipped with a special reading instrument. This process is shown here. When reading, a device comprising a main body mounted on the waist of an operator, a grip, a stick and a rod antenna is used. In order to read the sensor, the rod antenna is moved along a tread surface. Special care needed to be taken in the design of the sensor so that individual tyres could be read, an especially difficult process when dual tyres are being used, as here.
The Tyre Itself as the Sensor
However, the potentially most major development in Intelligent Tyres is being undertaken by Continental. Their plan is nothing less than to use the whole tyre as the sensor! Their US patent 6,308,758 (October 30, 2001) describes the use of tyres built with ferromagnetic powder within the rubber. After vulcanisation, the particles are magnetised in alternating polarisation bands all around the tyre. Monitoring the tyre are two magnetoresistant sensors that are mounted on the vehicle's suspension.
Continental has dubbed the system the Sidewall Torsion Sensor (SWT), and it is due to go into volume production as early as 2003.
The trick is apparently in designing the tyre so that there is a sharp 'edge' between the different magnetic fields, with Continental achieving this by the use of ribs within the tyre. By using 96 radial ribs in a conventional passenger car tyre, it is feasible to measure the lines of magnetic flux at even low speed.
This diagram shows the pattern of magnetization. The tyre (1) is depicted with a sidewall (2) having a magnetized outer layer (3). The sidewall outer layer is peripherally divided into sections (4) and (5) with radial ribs (6) between each adjacent pair of sections (4 and 5).
However, while measuring the speed of tyre rotation is one obvious outcome of taking this approach, Continental claim that much more is possible. Their patent states:
"Some of the information which can be determined using the present invention include the rotational speed of the tyre, the angular position of the tyre, the lateral or cornering forces on the tyre, the radial forces on the tyre, and the longitudinal forces on the tyre (eg sidewall torsion, torques, and fore-aft forces). For example, in order to determine the sidewall torsion, a tone wheel [toothed sensor] can be attached to a vehicle chassis and used to compare the location of the radially inner and outer portions of the ribs. The results of such a comparison are used to determine the sidewall torsion of the tyre. The determination of accurate information relating to the dynamic behaviour of the tyre depends on the precise measurement of the lines of magnetic flux. By enabling such a precise measurement, the present invention provides for a more accurate determination of the information."
If in fact this technology is feasible, it opens up a mind-boggling array of potential applications. For example, car control systems could use this technology to sense actual braking and acceleration grip (so taking into account road surfaces, tyre temperature, tyre rubber age, tyre pressure, damper condition, etc) in addition to sensing tyre degradation, damage, pressure or temperature changes. Once integrated into the tyre manufacturing process, it would also be a quite cheap technology to employ.
Quoted in Automotive Design and Production, Jim Giustino, senior research associate of Continental General Tyre, says, "The tyre is fundamentally where everything happens: ride, handling, safety, stopping."
And that would make sensing directly from the tyre itself absolutely invaluable.
Next week: tyre pressure monitoring.
