Patent Application
20070279204
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
One aspect of the present invention is a method of tire condition monitoring, including monitoring of tire inflation, which is accurate, inexpensive and simple to implement. This method includes electromagnetic response detection of amorphous metal ribbon or wire embedded inside a tire protector. Amorphous ferromagnetic materials may be very sensitive to mechanical stresses. For example, it is known that merit factor for “METGLASS” amorphous metal ribbon may reach a value of 1500, which is substantially higher than that for other known materials. Merit factor is defined as a ratio: F=(δZ/Z0)/δε Where Z0 is an impedance of a magnetic material, δZ is a change of the impedance under an applied stress, and δε is a deformation of the magnetic material under applied stress (i.e., δε=Δl/l, l is a length of magnetic material). By way of comparison, the merit factor for a semiconductor material may reach a value of only 100, and the merit factor for a metal foil and wire may reach only a value of 2.
An amorphous metal ribbon or wire interrogated by an alternating magnetic field will produce an electromagnetic response, and parameters such as amplitude and spectrum of harmonics of the electromagnetic response will depend on a mechanical stress applied to the amorphous metal ribbon or wire. An example of the effect of mechanical stress on electromagnetic response R is shown over time T in
Amorphous metal ribbon or wire may be embedded in a tire during tire fabrication. Automobile users will not feel any difference in using tires with embedded amorphous metal ribbons or wires in comparison with conventional tires.
In one embodiment of the present invention, a radiating device made of amorphous metal ribbon, such as a Co-based amorphous metal ribbon with negative magnetostriction, is embedded inside the tire protector for measurements of tire inflation. Amorphous metal ribbon with negative magnetostriction is characterized by high sensitivity to mechanical stress over a wide range of stress levels. This ribbon demonstrates high permeability under stress-free conditions. With the increase of applied stress, the permeability of the ribbon drops. Thus, by subjecting the ribbon to an alternating magnetic field interrogation by an interrogating device, the mechanical stress of the ribbon may be determined by sensing a resulting magnetic field at a sensing device. Further, the tire condition and in particular the tire inflation may be determined from the determined ribbon stress.
In this embodiment, an intermodulation response of an embedded amorphous metal ribbon is used for tire inflation measurement. The ribbon is interrogated by an alternating magnetic field produced by an interrogating device and having two substantially different frequency components. The first frequency is, for example, 8 kHz and the second frequency is, for example, 12 Hz. The ribbon undergoes magnetization at the first frequency of 8 kHz and generates an electromagnetic response at high harmonics of the interrogating frequency. Further, the radiating device ribbon generates the electromagnetic response by passive radiation (i.e., without the use of an external electrically connected power source or amplifier). In this embodiment, an electromagnetic response at the second harmonic of the first frequency (i.e., 16 kHz) is detected. The second low frequency magnetic field (i.e., the field produced in this example by the 12 Hz frequency component) is used for periodical sweeping amorphous metal ribbon between saturated states. While sweeping, the amorphous metal ribbon passes through a state at which its permeability reaches maximum. At the state close to maximum magnetic permeability, the amorphous metal ribbon exhibits the highest electromagnetic response. The higher electromagnetic response, the greater the detected signal. In addition, it is important to detect the electromagnetic response at the same state of amorphous metal ribbon (i.e., at state of maximum permeability) to eliminate the effect of an external DC magnetic field. The use of two magnetic fields allows high accuracy in measurement to be achieved, because using two frequencies may exclude the effect of external DC magnetic fields, such as the Earth magnetic field, on the measurement results.
For example, it is known that external magnetic field does not affect the maximum permeability of magnetic material. It may only shift magnetic material to the state where permeability is not maximum. Electromagnetic response in this shifted state will be lower than a response in the state close to maximum permeability. Excessive tension in the ribbon also decreases electromagnetic response, but it is due to decreasing of maximum permeability. The maximum permeability may serve as a parameter for tension measurement. For this reason, it is useful to detect signal response when magnetic material is close to the state of maximum permeability. The two-frequency technique described herein allows discrimination between the effects of tension and the effects of an external magnetic field. The receiving device may pick-up the maximum signal throughout the period of the lower interrogating frequency. This signal depends on tension only because it is detected when magnetic material is close to the state of maximum permeability.
A schematic diagram of an embodiment of the present invention is shown in
Another aspect of the present invention is a system for tire condition monitoring. The system includes of vehicle wheels with embedded amorphous metal ribbons or wires, at least one device for interrogation of embedded ribbons or wires and detection of their responses, and a central computer of the vehicle, which receives information from all detector units, analyses this information, and displays it in a form convenient for the vehicle driver. In case a substantial deviation of tire condition from normal state is registered, the computer provides a warning to the driver. The detector units are installed at the non-rotating base of the vehicle close to each wheel. There is no need for mechanical or electrical links between the vehicle's base and the rotating wheels since interrogation of amorphous metal ribbons or wires is produced exclusively through electromagnetic fields. In other words, the amorphous metal ribbon or wire is electrically isolated from the interrogating and sensing devices, and the amorphous metal ribbon or wire is a passive device that does not require an external electrically connected power source.
In another embodiment of the present invention, at least one amorphous wire with negative magnetostriction is embedded in the tire as one or more of the filaments in the tire cord thread (not shown in the drawings). This at least one amorphous wire can be for example, an in-water-cast wire or a glass-coated amorphous wire. Glass-coated amorphous wires are preferable since these can be manufactured in a non-expensive, one-stage process, with high mechanical strength and consistent dimensions. For example, wires of Cobalt-based alloy containing 10% boron and 15% silicon by atomic percentage can be used, with metal core diameters of 30 to 50 microns, and with glass coat thickness of 2 to 10 microns.
The process of the wire response detection and the determination of the tire inflation in the present embodiment can be performed similarly to the process described in the previous embodiment.
The present system for tire condition monitoring features substantial advantages in comparison with conventional systems.
It should be understood that the invention is disclosed by the way of non-limiting examples only. Those skilled in the art will readily appreciate that various modifications and changes can be applied to the invention as hereinbefore exemplified without departing from its scope defined in and by the appended claims.
Numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.
