Apparatus for monitoring tire pressure

CROSS REFERENCE TO RELATED APPLICATIONS

0001This application claims priority to U.S. Provisional Patent Application Ser. No. 60/467,498 filed on May 2, 2003, which is herein incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

00021. Field of the Invention

0003The present invention relates to an apparatus that monitors tire pressure. More particularly, the present invention relates to an apparatus that remotely excites a device in a tire, detects data from the device, and processes and displays the data as a tire pressure of the tire to a vehicle operator.

00042. Description of the Related Art

0005On board tire pressure sensing devices are known in the art. The tire pressure sensing devices are a convenience to vehicle operators and also a safety feature that has been mandated by the National Highway Traffic Safety Administration (41 CFR Part 571) for reducing the incidence of accidents caused by under-inflated tires. In the final ruling issued by NHTSA, two basic systems for tire pressure monitoring were described. More particularly, direct and indirect pressure measurement devices were described.

0006The indirect tire pressure monitoring systems are found through the rotational speeds as measured by the vehicle's anti-lock braking system (ABS). Although this system has the advantage of using equipment already installed on many vehicles, there are at least two major problems. First, sensitivity is a problem. Second, the indirect tire pressure monitoring systems may not identify critical combinations of multiple under-inflated tires. Since the indirect tire pressure monitoring systems operate by comparing the rotation speeds of individual tires, if a vehicle's tires are uniformly under-inflated, the system will not detect any rotational difference.

0007Direct tire pressure monitoring systems have sensitivity and an ability to resolve the inflation situation in each respective tire. A complication exists in accessing the information from within the rotating body of the tire. A direct electrical connection to any device becomes impractical because the tire rotates. The tire is also in an aggressive environment and any tire pressure monitoring system needs to be easily removable from the vehicle. Consequently, a practical approach for directly monitoring tire pressure is to use some sort of non-contact sensor device. An electronic pressure sensor coupled to a battery-powered radio frequency transmitter is known in the art. Tire pressure is relayed to the operator through a central receiver that identifies each tire and a pressurization state of the tire.

0008The main advantages of such direct tire pressure monitoring systems are increased sensitivity, an elimination of confounding variables present in the indirect tire pressuring monitoring system, and an ability to measure pressure in a stationary vehicle.

0009The direct tire pressure monitoring systems also suffer from a number of drawbacks. The direct tire pressure monitoring system is complex and expensive. The direct tire pressure monitoring system is also heavy and this device weight could potentially affect tire balance itself. Further, direct tire pressure monitoring systems have negative issues with regard to a battery life and battery disposal.

0010Remotely queried sensor systems unrelated to monitoring tire pressure are known in the art. An example of one such passive device is an electronic article surveillance (EAS) marker. The marker has a resonant circuit created by an antenna and a diode. Alternatively, the resonant circuit has the antenna with a capacitor combination. When interrogated by an alternating electromagnetic field, the circuit resonates. Thereafter, the circuit generates harmonics of the incident field. The receiving antenna detects either the generated harmonics or a depletion of an incident field. However, there are problems with such a system as the broad bandwidth and low amplitude of the harmonics makes these markers difficult to detect reliably.

0011In another example of the electronic article surveillance marker, the marker has a high magnetic permeability element. The high magnetic permeability element is placed adjacent to an element of higher magnetic coercivity. The high magnetic permeability element being adjacent to the element of higher magnetic coercivity resonates when interrogated by an alternating electromagnetic field due to nonlinear magnetic properties. The high magnetic permeability element adjacent to the element of higher magnetic coercivity generates harmonics of the interrogating frequency that are detected by a receiving coil.

0012For these electronic article surveillance markers, harmonics detection is difficult because of low amplitude. It is also complicated by the presence of other nonlinear ferromagnetic objects within the interrogation area, such as for example articles of magnetic recording material.

0013U.S. Pat. Nos. 4,510,489 and 4,510,490 to Anderson, III, et al., (hereinafter collectively as “Anderson”) disclose magneto-mechanical electronic article surveillance. The marker has a thin strip of magnetostrictive ferromagnetic material. The magnetostrictive ferromagnetic material is placed adjacent to a magnetic element of higher coercivity (hereinafter “a magnetically hard element”). A non-alternating magnetic bias is placed on the magnetostrictive ferromagnetic material, and causes a mechanical strain in the magnetostrictive ferromagnetic material. This strain affects a resonant frequency of the magnetostrictive ferromagnetic material. The device is designed with appropriate dimensions and magnetic properties to mechanically resonate at a predetermined frequency when interrogated by an incident alternating magnetic field.

0014The resonance of the magnetostrictive ferromagnetic material can be detected electromagnetically. The magneto-mechanical electronic article surveillance marker thus has advantages over previous electromagnetic markers of high sensitivity, high operating reliability and low manufacturing cost.

0015Magnetostriction is a property of a ferromagnetic material that changes volume when subjected to a magnetic field. When biased by a non-alternating magnetic field, magnetostrictive material stores energy via mechanical strain. This storage, affects the Young's modulus, E, of the material. Such magnetostrictive materials can be caused to resonate in an alternating magnetic field. The fundamental resonant frequency, FR, of a magnetostrictive ribbon can be described as a function F: <br /><i>FR=F</i>(<i>L,E</i>,ρ,σ) <br /> where L is the ribbon length, ρ is a density, and σ is the Poisson ratio.

0017The relationship between the biasing non-alternating magnetic field strength, Young's modulus and the resonant frequency attained by the magnetostrictive strip is more complicated. Variations in the biasing magnetic field strength shift a frequency at which a maximum amplitude response is created (the resonant frequency). The system's resonant frequency can be designed by varying a geometry, one or more mechanical properties of the magnetostrictive material, and a strength of the biasing non-alternating magnetic field. Mechanical processes such as annealing can further manipulate one or more mechanical properties thereof.

0018U.S. Pat. No. 5,628,840 to Hasegawa discloses a composition of a magnetostrictive material with relatively linear magnetic behavior. Hasegawa further discloses a response of the composition in a resonant frequency versus a bias field. This magnetostrictive material has an advantage in magneto-mechanical electronic article surveillance markers of providing a relatively strong signal for harmonic detection.

0019A number of vibrations of the magnetostrictive element can be damped by a mechanical interaction. Therefore, the device preferably has the magnetostrictive element in a chamber and capable of movement. Also, the biasing magnet preferably is optimal so as not to attract the magnetostrictive element to impede free movement. U.S. Pat. No. 5,499,015 to Winkler, et al. (hereinafter “Winkler”) discloses a resonant chamber. The resonant chamber is in a retail product or package.

0020U.S. Pat. No. 6,393,921 B1 to Grimes, et al. discloses a number of magnetostrictive materials in an assembly. The assembly measures pressure remotely, without any direct electrical hardwire connection. The assembly has a magnetostrictive strip that is held adjacent to a diaphragm. A magnetically hard element is connected to the diaphragm. As pressure changes, a deflection of the diaphragm occurs. This deflection changes the proximity of the magnetically hard element relative to the magnetostrictive element. The non-alternating magnetic bias on the magnetostrictive element changes which results in a change of the magneto-mechanical resonant frequency when subjected to an alternating magnetic field. The resonance can be remotely sensed by electromagnetic devices.

0021Grimes discloses an embodiment where the magnetostrictive material is in a pressure sensor. The pressure sensor has the magnetostrictive materials and the magnetically hard element in a defined proximity to each other to provide a constant non-alternating magnetic biasing field applied to the magnetostrictive element. Grimes further discloses that the magnetostrictive element has a mechanically hardened region.

0022A density change in a gas surrounding the pressure sensor is associated with a pressure change. This pressure change thus causes a shift in resonant frequency. In both disclosed embodiments, the interrogating signal and receiver scans a number of frequencies. This scanning locates a resonant peak, and relates a frequency to a pressure datum. Also disclosed is a method which excites with an impulse and uses a fast Fourier transform (FFT) to find a number of resonant peaks.

0023However, there are known problems associated with such a pressure sensor. The magnetostrictive response is temperature sensitive, primarily due to a dependence on Young's modulus. Consequently, the pressure sensor of Grimes requires independent temperature correction. For the purpose of determining a thermal drift of the pressure sensor, a correcting temperature measurement can be made with another second test device similar to the pressure sensor, that is not exposed to any varying non-alternating bias field strength or that is not exposed to any changing gas density, and that is in the same thermal environment as the pressure sensor.

0024Accordingly, there is a need for a tire pressure monitoring system that eliminates one or more of the aforementioned drawbacks and deficiencies of the prior art.

SUMMARY OF THE INVENTION

0025It is an object of the present invention to provide a tire pressure monitoring apparatus that can easily be applied to and removed from a tire.

0026It is another object of the present invention to provide a tire pressure monitoring apparatus with a sensor in the tire that is not physically connected to a transmitter and receiver system located outside the tire.

0027It is still another object of the present invention to provide a tire pressure monitoring apparatus with a display that communicates a tire pressurization state of the tire to a vehicle operator.

0028It is yet another object of the present invention to provide a tire pressure monitoring apparatus that has a magneto-mechanical pressure sensor in the tire that is resilient to withstand the operational environment in the tire.

0029It is still yet another object of the present invention to provide a tire pressure monitoring apparatus that has a magneto-mechanical pressure sensor in a sidewall of the tire.

0030It is a further object of the present invention to provide a tire pressure monitoring apparatus that has a number of magneto-mechanical pressure sensors in one or more locations in the tire.

0031It is a still further object of the present invention to provide a tire pressure monitoring apparatus that has a magneto-mechanical pressure sensor that emits a data parameter from the tire.

0032It is a yet further object of the present invention to provide a tire pressure monitoring apparatus that has a magneto-mechanical pressure sensor that emits such a data parameter from the tire that can be received electro-magnetically.

0033It is a still yet further object of the present invention to provide a tire pressure monitoring apparatus that has a magneto-mechanical pressure sensor that does not require any power source such as a battery connected to the magneto-mechanical pressure sensor.

0034It is an additional object of the present invention to provide a tire pressure monitoring apparatus that has a magneto-mechanical pressure sensor that does not interfere with a performance characteristic of the tire.

0035These and other objects and advantages of the present invention are achieved by an apparatus for monitoring a tire pressurization state. The apparatus for monitoring the tire pressurization state in a tire has a magneto-mechanical pressure sensor and an electro magnetic excitation system. The electro-magnetic excitation system interrogates the magneto-mechanical pressure sensor. The apparatus further has a receiver for receiving information from the electro magnetic excitation system and a data interpretation system. The data interpretation system translates the received information into the tire pressurization state. The data interpretation system is connected to a display and the display communicates the tire pressurization state to an operator.

DESCRIPTION OF THE DRAWINGS

0036<figref idref="DRAWINGS">FIG. 1</figref> is a sectional view of a tire wheel system having an apparatus for monitoring a tire pressurization state of the tire of the present invention.

0037<figref idref="DRAWINGS">FIG. 2</figref> is a sectional side view of an embodiment of the first magneto-mechanical pressure sensor of <figref idref="DRAWINGS">FIG. 1</figref>.

0038<figref idref="DRAWINGS">FIG. 3</figref> is side sectional view of the first magneto-mechanical pressure sensor of <figref idref="DRAWINGS">FIG. 2</figref> with a magnetostrictive element having a first end connected to a wall and a second free end.

0039<figref idref="DRAWINGS">FIG. 4</figref> is a side sectional view of a second embodiment of the first magneto-mechanical pressure sensor of <figref idref="DRAWINGS">FIG. 1</figref>.

0040<figref idref="DRAWINGS">FIG. 5</figref> is a side sectional view of a third embodiment of the magneto-mechanical pressure sensor of <figref idref="DRAWINGS">FIG. 1</figref>.

0041<figref idref="DRAWINGS">FIG. 6</figref> is a side sectional view of a fourth embodiment of the magneto-mechanical pressure sensor of <figref idref="DRAWINGS">FIG. 1</figref>, but being formed in a sidewall of the tire.

0042<figref idref="DRAWINGS">FIG. 7</figref> is side sectional view of a fifth embodiment of the magneto-mechanical pressure sensor of <figref idref="DRAWINGS">FIG. 1</figref>.

0043<figref idref="DRAWINGS">FIG. 8</figref> is a side sectional view of a sixth embodiment of the magneto-mechanical pressure sensor of <figref idref="DRAWINGS">FIG. 1</figref>.

0044<figref idref="DRAWINGS">FIG. 9</figref> is a side sectional view of a seventh embodiment of the magneto-mechanical pressure sensor of <figref idref="DRAWINGS">FIG. 1</figref>.

0045<figref idref="DRAWINGS">FIG. 10</figref> is a side sectional view of an eighth embodiment of the first magneto-mechanical pressure sensor of <figref idref="DRAWINGS">FIG. 1</figref> having a clamp to adjust a length of a magnetostrictive element.

0046<figref idref="DRAWINGS">FIG. 11</figref> is a circuit diagram of a data interpretation system of the present invention.

0047<figref idref="DRAWINGS">FIG. 12</figref> is a second embodiment of a circuit diagram of a data interpretation system of the present invention.

0048<figref idref="DRAWINGS">FIG. 13</figref> is a third embodiment of a circuit diagram of a data interpretation system of the present invention.

0049<figref idref="DRAWINGS">FIG. 14</figref> is a graph showing a response amplitude of the magneto-mechanical pressure sensor of present invention.

0050<figref idref="DRAWINGS">FIG. 15</figref> is a second graph of a first, a second and a third resonance response of the discrete magneto mechanical pressure sensor of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

0051Referring to the drawings and, in particular <figref idref="DRAWINGS">FIG. 1</figref>, the present invention is an apparatus generally referred to by reference numeral <b>10</b> for monitoring a tire pressurization state in a tire <b>12</b> for a transportation device. The transportation device may be any transportation device such as a motorcycle, a truck, an automobile, a sports utility vehicle, an aircraft, a scooter, a bicycle, a unicycle or any other device, using one or more pneumatic tires, that is known in the art.

0052The apparatus <b>10</b> preferably has high durability so as to be used in an aggressive operating environment and under strenuous operating conditions such as driving at high speeds. The apparatus <b>10</b> can preferably be jostled and undergo high stresses and high strains relative to strenuous driving conditions, without failure.

0053The tire <b>12</b> is made of rubber reinforced with cords of nylon, fiberglass, or other material and filled with compressed air. The tire <b>12</b>, which shown in a cross sectional view, has a covering. The covering or outer edge perimeter <b>14</b> of the tire <b>12</b> preferably contacts ground. The tire <b>12</b> is further mounted on a wheel rim <b>16</b>. The wheel rim <b>16</b>, which is known in the art, is preferably positioned in a location that is adjacent to a compartment <b>18</b> in the transportation device. The tire <b>12</b> preferably supports the transportation device. In the preferred embodiment of use of the tire <b>12</b>, namely on an automobile, the compartment <b>18</b> is preferably a wheel well or side panel of the automobile or any other suitable location near the tire <b>12</b>. The compartment <b>18</b> preferably has an interior space therein. The compartment <b>18</b> preferably receives one or more components of the apparatus <b>10</b>.

0054The apparatus <b>10</b> preferably has a magneto-mechanical pressure sensor <b>20</b>, an electromagnetic excitation system <b>22</b> to interrogate the magneto-mechanical pressure sensor, a receiver <b>24</b> that measures the magneto-mechanical pressure sensor's resonant characteristics, and a data interpretation system <b>26</b>. The receiver <b>24</b> and the data interpretation system <b>26</b> are shown in <figref idref="DRAWINGS">FIGS. 11 through 13</figref> and discussed later herein. The data interpretation system <b>26</b> preferably translates a resonant characteristic of the magneto-mechanical pressure sensor <b>20</b> and converts this resonant characteristic to a tire pressurization state. Then, data interpretation system <b>26</b> displays the tire pressurization state to a vehicle operator.

0055Most preferably, the apparatus <b>10</b> has the magneto-mechanical pressure sensor <b>20</b> that does not require any independent power source, and thus does not have any physical connection or wires entering or exiting from the tire <b>12</b> for providing any power that may complicate operation. The apparatus <b>10</b> is low in cost. Preferably, the apparatus <b>10</b> has one or more components that are fabricated as an integral unit to the tire <b>12</b>. However, this is not necessary and the unit may be fabricated independently and later attached in some manner to the tire <b>12</b> or alternatively the tire rim.

0056Referring to <figref idref="DRAWINGS">FIG. 1</figref>, there is shown a number of magneto-mechanical pressure sensors <b>20</b>. These pressure sensors <b>20</b> are positioned at one or more locations in the interior of the tire <b>12</b> preferably on an opposite side of the ground contacting covering portion <b>14</b>. Alternatively, the number of magneto-mechanical pressure sensors <b>20</b> can be mounted to the wheel rim <b>16</b>. Still alternatively, the number of magneto-mechanical pressure sensors <b>20</b> can be placed beneath a tread of the covering portion <b>14</b> of the tire <b>12</b> or alternatively in a portion of a valve stem assembly. However, one skilled in the art should appreciate that in all embodiments, the number of magneto-mechanical pressure sensors <b>20</b> most preferably are in relatively close proximity to the electromagnetic excitation system <b>22</b> to receive an electromagnetic field therefrom.

0057Preferably, the electromagnetic excitation system <b>22</b> has a number of coils, or more particularly an excitation coil <b>28</b> and a receiving coil <b>30</b> shown in <figref idref="DRAWINGS">FIG. 11</figref>. The electromagnetic excitation system <b>22</b> is preferably operatively connected to the receiver <b>24</b> and the data interpretation system <b>26</b>.

0058As shown in <figref idref="DRAWINGS">FIG. 1</figref>, one skilled in the art should appreciate that the magneto-mechanical pressure sensor <b>20</b> could be mounted in a number of locations. For example, the magneto-mechanical pressure sensor could be mounted on a tire sidewall, inside the tire sidewall, on the wheel itself, or even molded as an integral feature of the tire wall, or any combinations thereof. Preferably, the magneto-mechanical pressure sensor <b>20</b> regardless of the location has a magnetostrictive element oriented in a direction complementary to a centrifugal force of the tire <b>12</b> so as not to impede the electromechanical resonance of the magnetostrictive element.

0059Two approaches, discrete and continuous, are disclosed for using a magneto-mechanical element with the magneto-mechanical pressure sensor <b>20</b> in the apparatus <b>10</b>. In the continuous approach, the magneto-mechanical pressure sensor <b>20</b> preferably measures a resonance of the magnetostrictive element continuously as a function of pressure. In the discrete approach, the magnetostrictive element of the magneto-mechanical pressure sensor <b>20</b> are sensed in either an “on” or “off” state as a function of pressure, indicating certain predetermined pressure threshold values. In this embodiment, the pressurization state of the tire <b>12</b> is thus interpreted from a combination of on/off signals received by the receiver <b>24</b>. It should be also noted that the “on” and “off” states may be implemented as “resonate” and “don't resonate”. Alternatively, “on” state and “off” state may be implemented as “resonate at frequency A” and “resonate at frequency B”.

0060In one embodiment, a continuous magneto-mechanical pressure sensor <b>20</b> is used. However, one skilled in the art should appreciate that the apparatus <b>10</b> may be used either with the continuous magneto-mechanical pressure sensor, a discrete magneto-mechanical pressure sensor or any combination thereof.

0061Referring to <figref idref="DRAWINGS">FIG. 2</figref>, there is shown a preferred embodiment of the magneto-mechanical pressure sensor <b>20</b> of the apparatus <b>10</b> of the present invention. Each magneto-mechanical pressure sensor <b>20</b> preferably has a housing <b>32</b>. The housing <b>32</b> preferably has an interior space therein for protecting the components of the magneto-mechanical pressure sensor <b>20</b>. Each magneto-mechanical pressure sensor <b>20</b> preferably has a magnetically hard element <b>34</b> connected to a member <b>36</b>, and a magnetostrictive element <b>38</b> in spaced relation from the magnetically hard element in the tire <b>12</b>. The magnetically hard element <b>34</b> is preferably a magnetic element of relatively higher coercivity. One skilled in the art should appreciate that the magnetostrictive element <b>38</b> may be any magnetostrictive material known in the art including but not limited to alloys of iron, cobalt, yttrium, gadolinium, terbium, dysprosium, or any combinations thereof.

0062Preferably, the magneto-mechanical pressure sensor <b>20</b>, when undergoing a linear motion, changes a proximity between the magnetically hard element <b>34</b> and the magnetostrictive element <b>38</b>. In doing so, the magneto-mechanical pressure sensor <b>20</b> causes a change in a non-alternating bias field strength experienced by the magnetostrictive element <b>38</b>, and thus shifts the peak resonant frequency exhibited by the magnetostrictive element when interrogated with an alternating magnetic field from the electromagnetic excitation system <b>22</b>.

0063Preferably, the magnetically hard element <b>34</b> or the magnetostrictive element <b>38</b> is mounted on a moving portion of the magneto-mechanical pressure sensor <b>20</b>. The other element of the magnetically hard element or the magnetostrictive element is mounted in a stationary manner. The magneto-mechanical pressure sensor <b>20</b> preferably determines the tire pressurization state by referencing a known pressure. Thus, the magneto-mechanical pressure sensor <b>20</b> preferably has a reference pressure chamber <b>40</b>. Alternatively, the reference pressure chamber <b>40</b> may use atmospheric pressure external to the tire <b>12</b> as the reference pressure.

0064Referring again to <figref idref="DRAWINGS">FIG. 2</figref>, a preferred feature of the present invention is that the magnetostrictive element <b>38</b> is not mechanically damped. In a preferred embodiment of the present invention, the magnetostrictive element <b>38</b> has a major axis <b>42</b> that is aligned radially relative to the tire <b>12</b>. Preferably, the magnetostrictive element <b>38</b> has suitable dimensions and has a suitable shape to maintain centering the magnetostrictive element in interior of the tire <b>12</b>. Alternatively, the magnetostrictive element <b>38</b> may be anchored. The anchoring preferably limits a mechanical dampening of the magnetostrictive element <b>38</b>, upon rotation of the tire <b>12</b> during, for example, driving.

0065Alternatively, the magnetostrictive element <b>38</b> may have a central node (not shown). The magnetostrictive element <b>38</b> may be held in the tire <b>12</b> at the central node or alternatively at either end by a mounting device, such as a mounting pin or a thin jawed clamp. One skilled in the art should appreciate that the magnetostrictive element <b>38</b> may be mounted in any suitable manner known in the art to orient the device radially with respect to the tire's <b>12</b> rotation in order to keep a free end or ends of the magnetostrictive element from being deflected away from the magnetically hard element <b>34</b> due to the centrifugal force.

0066The member <b>36</b> of the magneto-mechanical pressure sensor <b>20</b> is a sealed bellows. In this example, the sealed bellows <b>36</b> is sealed with a reference pressure. A variation in the tire pressure is illustrated as reference numeral <b>44</b>. The variation causes the magnetically hard element <b>34</b> to move with respect to the magnetostrictive element <b>38</b>. The magnetostrictive element <b>38</b> is preferably held in the housing <b>32</b>, however the magnetostrictive element is preferably free to resonate, but anchored with respect to an inner radius of the tire <b>12</b>. In this manner, the magnetostrictive element <b>38</b> is stabilized against the centrifugal forces experienced in the tire <b>12</b> upon rotation.

0067Referring to <figref idref="DRAWINGS">FIG. 3</figref>, there is shown a preferred orientation and anchoring of the magnetostrictive element <b>38</b>. Alternatively, the magnetostrictive element <b>38</b> may be anchored at a centermost portion as shown in a middle of the magnetostrictive element as reference numeral <b>46</b>, at any other location on a horizontal line going through the middle, or have both ends free floating in the tire <b>12</b>. However in the embodiment shown in <figref idref="DRAWINGS">FIG. 3</figref>, the magnetostrictive element <b>38</b> has one end connected in a cantilever fashion to the housing <b>32</b>.

0068Referring to <figref idref="DRAWINGS">FIG. 4</figref>, there is shown another or second preferred embodiment of the magneto-mechanical pressure sensor <b>20</b>. Similar to the embodiment of the magneto-mechanical pressure sensor <b>20</b> of <figref idref="DRAWINGS">FIGS. 2 and 3</figref>, the magneto-mechanical pressure sensor has magnetostrictive element <b>38</b> and magnetically hard element <b>34</b>. Preferably, the member <b>36</b> of the magneto-mechanical pressure sensor <b>20</b> of this embodiment is a diaphragm <b>48</b>. The diaphragm <b>48</b> preferably is a thin disk that is deflected in a manner that is proportional to the pressure difference between the two sides of the diaphragm. Preferably, the diaphragm <b>48</b> is connected to an interior wall of the housing <b>32</b> and acts as the reference pressure chamber <b>40</b>. In this embodiment, the diaphragm <b>48</b> moves in a manner as indicated by reference arrows <b>50</b>.

0069The magneto-mechanical pressure sensor <b>20</b> also has the magnetically hard element <b>34</b> that is closely adjacent to the diaphragm <b>48</b> and is spaced a predetermined distance away from the magnetostrictive element <b>38</b>. The housing <b>32</b> preferably has an opening that allows a first side of the diaphragm <b>48</b> to be exposed to air in the tire <b>12</b>, while the opposite or second side of the diaphragm is exposed to the reference pressure chamber <b>40</b>.

0070Referring to <figref idref="DRAWINGS">FIG. 5</figref>, there is shown another or third preferred embodiment of the magneto-mechanical pressure sensor <b>20</b> of the present invention. In this embodiment, the magneto-mechanical pressure sensor <b>20</b> preferably has the diaphragm <b>48</b> with a channel <b>52</b>. The channel <b>52</b> preferably is through the covering portion <b>14</b> of the tire <b>12</b> and communicates with ambient pressure outside of the tire. Thus, the channel <b>52</b> provides the diaphragm <b>48</b> with the reference pressure chamber <b>40</b> while the location on an opposite side of the diaphragm <b>48</b> communicates with the tire pressure <b>44</b>.

0071Referring to <figref idref="DRAWINGS">FIG. 6</figref>, there is shown still another or fourth preferred embodiment of the magneto-mechanical pressure sensor <b>20</b> of the present invention. In this preferred embodiment, the magneto-mechanical pressure sensor <b>20</b> is formed in the tire <b>12</b> on an opposite side of the ground-contacting portion of the covering portion <b>14</b> of the tire. The magneto-mechanical pressure sensor <b>20</b> has the magnetically hard element <b>34</b> in the tire <b>12</b>, preferably in the side wall of the tire. Preferably, an indentation in the side wall is formed by removing a portion of the tire <b>12</b> and the magnetically hard element <b>34</b> is in the complementary sized indentation. Alternatively, the sensor <b>20</b> could be an integral addition to the inside sidewall to preserve the mechanical integrity of the tire <b>12</b>. The magneto-mechanical pressure sensor <b>20</b> preferably has a frame <b>54</b>. The frame <b>54</b> is a support structure that is connected to one or more notches <b>56</b>, <b>58</b> in the side wall of the tire <b>12</b>.

0072The magneto-mechanical pressure sensor <b>20</b> preferably has the diaphragm <b>48</b> formed as or in the side wall of the tire <b>12</b>. In this embodiment, the diaphragm <b>48</b> has a predetermined flexing property. The magnetostrictive element <b>38</b> is preferably connected to the frame <b>54</b>. The magnetostrictive element <b>38</b> is mounted to the frame <b>54</b> by one or more mechanical fasteners that preferably will not substantially affect a resonance frequency of the magneto-mechanical pressure sensor <b>20</b>. Preferably, the frame <b>54</b> is held substantially stationary relative to a rim of the diaphragm <b>48</b> by the notches <b>56</b>, <b>58</b>.

0073Preferably, the frame <b>13</b> has sufficient rigidity to maintain stability and a mechanical performance of the tire <b>12</b>. Also, the sufficient rigidity of the frame <b>13</b> prevents or virtually prevents any holes from forming through the covering portion <b>14</b> of the tire <b>12</b>.

0074In this manner, any variation in the tire pressure <b>44</b> will change a distance <b>60</b> between the magnetically hard element <b>34</b> and the magnetostrictive element <b>38</b>. This change in distance <b>60</b> will thus vary a non alternating magnetic bias on the magnetostrictive element <b>38</b> as a function of pressure that will be detected by the interrogation of the electromagnetic excitation system <b>22</b> as indicated by reference arrow <b>62</b>.

0075In another embodiment of the present invention, the magneto-mechanical pressure sensor <b>20</b> may have the magnetostrictive element <b>38</b> moving in a rotary manner similar to a needle on a pressure gauge (not shown). The rotary motion magneto-mechanical pressure sensor, such as a Bourdon tube type pressure gauge, may rotate a non-alternating biasing magnet relative to the magnetostrictive element <b>38</b> shown in <figref idref="DRAWINGS">FIG. 6</figref>. The rotary motion is designed such that the magnetically hard element <b>34</b> and the magnetostrictive element <b>38</b> are preferably aligned relative to one another at either a highest tire pressure or a lowest tire pressure of the tire <b>12</b>. As the pressure changes, a degree of alignment of the non-alternating biasing magnetic field changes relative to the major axis <b>42</b> of the magnetostrictive element <b>38</b>, thus causing a shift in the resonant peak of the magnetically hard element <b>34</b> and the magnetostrictive element combination.

0076In another embodiment of the magneto-mechanical pressure sensor <b>20</b>, the apparatus <b>10</b> has a number of magnetostrictive elements <b>38</b> and magnetically hard elements <b>34</b>, or an array of sensors <b>20</b>. Each combination resonates at discernibly different predetermined frequencies for detection by the receiver <b>24</b>.

0077In still another or fifth preferred embodiment of the present invention, which is shown in <figref idref="DRAWINGS">FIG. 7</figref>, the magneto-mechanical pressure sensor <b>20</b> has a bi-stable, snap-acting disc <b>64</b>. The bi-stable, snap-acting disc <b>64</b> preferably toggles under a predetermined pressure differential in the pressure chamber <b>40</b>. Preferably, the bi-stable, snap-acting disc <b>64</b> toggles from a first position to a second position. In the first position, the magneto-mechanical pressure sensor <b>20</b> allows the magnetostrictive element <b>38</b> to electro-magnetically resonate. In the second position, the bi-stable, snap-acting disc <b>64</b> prevents and impedes the magnetostrictive element from resonating electro-magnetically. When the predetermined threshold pressure differential is exceeded, the bi-stable, snap-acting disc-<b>64</b> preferably toggles to the second position. Here, the stable, snap-acting disc <b>64</b> contacts the magnetostrictive element <b>38</b>, thus mechanically damping the electromagnetic resonance, placing the magneto-mechanical sensor <b>20</b> in an “off’ state.

0078Referring to <figref idref="DRAWINGS">FIG. 7</figref>, the magneto-mechanical pressure sensor <b>20</b> has a membrane <b>66</b>. The membrane <b>66</b> is preferably a support structure placed between the magnetically hard element <b>34</b> and the magnetostrictive element <b>38</b>. The membrane <b>66</b> prevents the magnetostrictive element <b>38</b> from contacting and being adhered to the magnetically hard element <b>34</b>, and thus prevents further operation of the magneto-mechanical pressure sensor <b>20</b>. The membrane <b>66</b> allows the magnetostrictive element <b>38</b> to reset because the bi-stable, snap-acting disc <b>64</b> moves from the second position to the first position, for example, during inflation of the tire <b>12</b>.

0079One skilled in the art will appreciate that the apparatus <b>10</b> may have an array of magneto-mechanical pressure sensors <b>20</b>. Each sensor <b>20</b> has the bi-stable, snap-acting disc <b>64</b> with different predetermined toggle pressure thresholds and different resonant frequencies. The array is read by determining which frequency elements have been damped. Alternatively, each magneto-mechanical pressure sensor <b>20</b> may resonate at the same frequency, even when located at a number of different angular positions along the tire <b>12</b>. The predetermined toggle threshold pressures of the bi-stable, snap-acting disc <b>64</b> is designed to be different at each position. In this embodiment, determination of the pressure inside the tire <b>12</b> can be accomplished by counting the number of pressure sensors <b>20</b> still resonating. The magneto-mechanical pressure sensors <b>20</b>, each with the bi-stable, snap-acting disc <b>64</b>, can be an integral feature of the tire <b>12</b>, for example in the sidewall of the tire.

0080In another embodiment of the present invention, the bi-stable, snap-acting disc <b>64</b> preferably may traverse from a first loading position upon an application of a first loading force and may traverse from the first loading position to a second unloading position upon an application of a second unloading force. The second unloading force may be different from the first unloading force or less than the first unloading force between the inflation and deflation of the tire <b>12</b>. A sensitivity of the apparatus <b>10</b> preferably depends from the bi-stable, snap-acting disc <b>64</b> being set at a normal inflation pressure, and that the bi-stable, snap-acting disc toggling reliably in an under-inflated situation of the tire <b>12</b>.

0081Referring to <figref idref="DRAWINGS">FIG. 8</figref>, in another or sixth preferred embodiment of the present invention, the magneto-mechanical pressure sensor <b>20</b> may have a discrete sensing device <b>68</b>. The discrete sensing device <b>68</b> preferably contacts and dampens the magnetostrictive element <b>36</b> at a predetermined pressure. The discrete sensing device <b>68</b> preferably dampens or changes a resonance characteristic of the magnetostrictive element <b>36</b>. The discrete sensing device <b>38</b> is preferably any device that touches the magnetostrictive element <b>36</b> and changes magnetostrictive element <b>36</b> to an “on” or an “off” state.

0082Referring to <figref idref="DRAWINGS">FIG. 9</figref>, in still another or seventh preferred embodiment of the present invention, the magneto-mechanical pressure sensor <b>20</b> may have the bi-stable, snap-acting disc <b>64</b> alternatively configured in a way that does not effect damping of the magnetostrictive element <b>38</b>. In this preferred embodiment, the hard magnetic element <b>34</b> is connected to a lateral side of the bi-stable, snap-acting disc <b>64</b>. The bi-stable, snap-acting disc <b>64</b> connected to the hard magnetic element <b>34</b> preferably toggles from the first position to the second position to indicate first and second tire pressurization states. To toggle from the first position to the second position, different resonant frequencies would be sensed thereby indicating the “on” or the “off’ state. Alternatively, the bi-stable, snap-acting disc <b>64</b> may be fabricated entirely from a magnetically hard material <b>34</b>.

0083Preferably, the data interpretation system <b>26</b> calculates pressure from the resonant frequency. The frequency is input into a transfer function that interprets the input as the pressure. One property of the magnetostrictive element <b>38</b> is that the frequency response is dependent on a temperature of the air in the tire. A temperature correction is necessary for the accurate interpretation of pressure in the magneto-mechanical pressure sensor <b>20</b>. A change position, velocity, and acceleration also affect a determination of resonant frequency of the magneto-mechanical pressure sensor <b>20</b> in the tire <b>12</b>. Compensation for these, as well as temperature effects, is needed to calculate pressure from the measured resonant frequency.

0084Referring to <figref idref="DRAWINGS">FIG. 10</figref>, in another embodiment of the present invention, the magnetostrictive element <b>38</b> preferably has an initial length and a first resonance frequency. The magneto-mechanical pressure sensor <b>28</b> may further have a member <b>69</b> that reduces or increases the initial length of the magnetostrictive element <b>38</b>. This reduction or increase in the length will modulate the first resonance frequency for later detection. Preferably, the member <b>69</b> is a clamp having a space therebetween for holding the magnetostrictive element <b>38</b> therein. The clamp <b>69</b> is preferably connected to a piston that communicates with a reference pressure at a first location and a tire pressure at a second location through an aperture. This change in pressure adjusts the length and thus the resonance frequency for later detection. A spring <b>71</b> is also provided in the magneto-mechanical pressure sensor <b>20</b> on a opposite side of the piston to effect a return when the length of the magnetostrictive element <b>38</b> based upon a pressure change in the tire <b>12</b> is reduced or increased.

0085In an eighth embodiment of the magneto-mechanical pressure sensor <b>20</b> the magneto-mechanical pressure sensor has a device for modulating the vibration of the magnetostrictive element <b>38</b>. Preferably, the magneto-mechanical pressure sensor <b>20</b> has a pointed clamp or clamping mechanism <b>70</b>. The pointed clamp mechanism <b>70</b> is connected to a location of the magnetostrictive element <b>38</b>. Preferably, the pointed clamp mechanism <b>70</b> is connected to a substantially middle location of the magnetostrictive element <b>38</b>. The pointed clamp mechanism <b>70</b> may be manipulated to move on the magnetostrictive element <b>38</b> to change a clamp point on the magnetostrictive element as a function of pressure. In this manner, the pointed clamp mechanism <b>70</b> preferably modulates the vibration of the magnetostrictive element <b>38</b> and thus changes the resonant frequency detected.

0086Referring to <figref idref="DRAWINGS">FIG. 11</figref>, there is shown a block diagram for the electromagnetic excitation system <b>22</b> for a continuous type magneto-mechanical pressure sensor <b>20</b> having the excitation coil <b>28</b>, the receiving coil <b>30</b>, a excitation oscillator <b>72</b> and receiving circuitry for the continuous monitoring of the tire pressure. The same circuitry preferably also monitors the resonant frequency responses of a temperature sensor (not shown). Alternatively, the excitation coil <b>28</b> and the receiving coil <b>30</b> may be reduced to functions of one coil. In this alternative embodiment, the coil may alternate in a time division multiplexed manner between an excitation function and a receiving function. The apparatus <b>10</b> has a data interpretation system <b>26</b>. The data interpretation system <b>26</b> has the controller <b>74</b>. The controller <b>74</b> is preferably a microprocessor or a digital signal processor that controls the excitation oscillator <b>72</b> that is connected to an excitation amplifier <b>71</b>, to detect peak responses, and to convert the peak responses from resonant frequency to the temperature and the tire pressure. The controller <b>74</b> preferably sets the frequency that the excitation oscillator <b>72</b> outputs.

0087A signal from the excitation oscillator <b>72</b> is current amplified and output to the excitation coil <b>28</b>. The output is exposed to the magneto-mechanical sensor <b>20</b>. The pickup coil <b>30</b>, which preferably is in a coaxial manner with the excitation coil <b>28</b>, receives a first signal directly from the excitation coil, and a second signal from the magneto-mechanical sensor <b>20</b>.

0088The data interpretation system <b>26</b> has a cancellation circuit <b>76</b>. The cancellation circuit <b>76</b> has a canceling coil therein (not shown). The canceling coil (not shown) preferably is wrapped in an opposite direction relative to pickup coil <b>30</b>, or alternatively is a phase shifted differencing amplifier. The resultant output from a pickup amplifier <b>78</b> (that is connected to the pickup coil <b>30</b> and the cancellation circuitry <b>76</b>) is substantially solely from the magneto-mechanical sensor <b>20</b>.

0089The data interpretation system <b>26</b> has a detector <b>80</b>. The detector <b>80</b> may be any circuitry known in the art that allows the controller <b>74</b> to measure peak amplitude of the output of the pickup amplifier <b>78</b>. The detector <b>80</b> may alternatively be a filtered rectifier, a peak detecting sample, a hold circuit, an analog to digital converter run by the controller <b>74</b> or any other type of amplitude demodulating circuitry. In another less preferred embodiment, the controller <b>74</b> may control the detector <b>80</b> in more digitally controlled embodiments.

0090Referring to <figref idref="DRAWINGS">FIG. 12</figref>, there is shown another or second embodiment of the data interpretation system <b>26</b> for a discrete type sensor <b>20</b> of the present invention. The oscillator <b>72</b> implements a single excitation frequency. The oscillator's output is a current that is amplified by the excitation amplifier <b>71</b> to drive the excitation coil <b>28</b> and emit the electromagnetic field in the tire <b>12</b>. In this embodiment, the pickup coil <b>30</b> is preferably a sensor receiver coil that picks up the magnetic field due to both the excitation coil <b>28</b> and the magneto-mechanical pressure sensor <b>20</b> in the tire <b>12</b>. The data interpretation system <b>26</b> has the cancellation circuit <b>76</b> that is connected between the pickup amplifier <b>78</b> and the excitation coil <b>28</b>. The cancellation circuit <b>76</b> removes any artifact of the excitation coil <b>28</b>. The cancellation circuit <b>76</b>, as in the embodiment of <figref idref="DRAWINGS">FIG. 12</figref>, may be a canceling coil (not shown) wrapped in the opposite direction from that of the pickup coil <b>30</b>, a differencing amplifier, or alternatively any other suitable device known in the art.

0091An alternating current output of the pickup amplifier <b>78</b> is run through a band pass filter <b>82</b> preferably centered at an expected ideal resonant frequency. This alternating current output outputs a band pass filtered signal. The band pass filtered signal is made unipolar by a rectifier collectively shown with the low pass filter as reference numeral <b>84</b>. The rectifier <b>84</b> is preferably a full or a half wave rectifier. The data interpretation system <b>26</b> has a low pass filter that is connected to the rectifier <b>84</b>. The low pass filter and rectifier <b>84</b> preferably provides a rectified signal that is smoothed by the low pass filter. The data interpretation system <b>26</b> has a comparator <b>86</b>, preferably a threshold comparator, connected to the low pass filter and the rectifier <b>84</b>. The smoothed rectified signal is then squared by the comparator <b>86</b>. Accordingly, an output <b>88</b> of the magneto-mechanical sensor <b>20</b> is seen as a square wave pulse for each rotation of the tire <b>12</b>.

0092Referring to <figref idref="DRAWINGS">FIG. 13</figref>, the data interpretation system <b>26</b> may be altered to serve a number of magneto-mechanical sensors <b>20</b>. The number of magneto-mechanical sensors <b>20</b> are preferably excited and detected as discussed. In this embodiment, the data interpretation system <b>26</b> has a complementary number of oscillators <b>100</b> preferably equal or almost equal to the number of magneto-mechanical pressure sensors <b>20</b> with each of the number of magneto-mechanical pressure sensors being centered on a different ideal resonant frequency.

0093The exciting frequencies are summed (or time division multiplexed) and amplified by the excitation amplifier <b>71</b>. One skilled in the art should appreciate that the signal synthesis and summation or multiplexing can readily be implemented by a second controller <b>101</b>.

0094The excitation coil <b>28</b> is preferably connected to the cancellation circuit <b>76</b> and the output of the cancellation circuit is input into the pick up amplifier <b>78</b>. The output of the pickup coil <b>30</b> from the number of magneto-mechanical pressure sensors <b>20</b> are connected to the pickup amplifier <b>78</b>. The data interpretation system <b>26</b> has a number of band pass filters <b>102</b> equal to the number of magneto-mechanical pressure sensors <b>20</b>. Each band pass filter <b>102</b> is preferably tuned and centered on a different predetermined ideal resonant frequency. One skilled in the art should appreciate the cancellation circuit <b>76</b> and the band pass filters <b>102</b> are wired in parallel relative to one another, and can also be alternatively implemented digitally. It can also be appreciated by those skilled in the art that an analog or digital single band pass filter with one or more corner frequencies may be controlled by the controller <b>74</b>. The outputs of the magneto-mechanical pressure sensors <b>20</b> are relayed to the pickup coil <b>30</b>, amplified then pass through the band pass filters <b>102</b> and are summed. The summed output is then rectified by the rectifier <b>84</b> and then smoothed by a low pass filter, and then squared by the comparator <b>86</b>.

0095Assuming each individual component magneto-mechanical discrete type pressure sensor <b>20</b> in, on or part of the tire <b>12</b> is rotationally offset on the tire, the output is a series of pulses for each tire. The number of pulses in each series is indicative of how many pressure thresholds have been exceeded (or not reached, depending on mechanical configuration). One skilled in the art should appreciate that detection of the magneto-mechanical pressure sensor <b>20</b> being in, on or part of the tire <b>12</b> could also be implemented by a peak detection technique, a phased-lock loop technique, a synchronized sampling technique, or any combinations thereof.

0096The pulse trains that are emitted or outputted by the apparatus <b>10</b> of each tire <b>12</b> are transmitted to a central circuit <b>104</b> that interprets the pulse trains. The central circuit <b>104</b> could be implemented by the controller <b>74</b>, preferably a microprocessor which times and counts the pulses, to determine how many magneto-mechanical pressure sensors <b>20</b> are above a predetermined threshold for a given tire <b>12</b>. The central circuit <b>104</b> then activates an indicator <b>106</b> or a display, on for example a dashboard, to alert the vehicle operator as to the tire pressurization state of each tire <b>12</b>. One skilled in the art should appreciate that the display <b>106</b> may be an analog display, a digital display, an indicator, a light emitting diode, an audible alarm or any other device for communicating data to the vehicle operator or another entity.

0097The data interpretation system <b>26</b> preferably uses a first method or sequence that preferably finds a temperature first, then based upon the temperature adjusts the pressure frequency estimate before searching for the pressure sensor peak. The first method has a first step of estimating resonant frequency of temperature channel that is equal to a last know resonance frequency. Thereafter, the method has a second step of searching for a resonance peak, then a third step of looking up temperature for a corrected resonance frequency. The method has a fourth step of estimating pressure that is equal to a last known pressure, and the fifth step of looking up expected resonant frequency for estimated pressure. The method further has a sixth step of correcting expected resonant frequency for a second temperature measurement and the seventh step of searching for a resonant peak. The method still further has an eighth step of looking up a temperature for a corrected resonant frequency and then outputting this value to repeat the method from the first step.

0098The data interpretation system <b>26</b> preferably uses a second method or sequence that preferably determines a resonance frequency of a temperature sensor or the magneto-mechanical pressure sensor <b>20</b> in a rotating environment of the tire <b>12</b>. The second method preferably has the first step a finding a resonance peak, then a second step of setting frequency A for a new predetermined estimate. The second method preferably has the third step of waiting for a detectable response, a fourth step of saving time of response, a fifth step of monitoring the response and recording a maximum amplitude. The second method also has a sixth step of calculating a time interval since the last response. The second method further has a seventh decision step of does the rotational velocity require a ring up correction, and if so, then the second method has the step of looking up the ring up correction for a rotational velocity and apply a correction to the output.

0099If the seventh decision step does not require a ring up correction, then the method has the next eighth decision step. The eighth decision step has the step of does the velocity require a centrifugal force correction, and if so the second method has the ninth step of looking up a ring up correction for a rotational velocity and then a tenth step of applying a correction to a maximum amplitude measured by this frequency. If the eighth decision step does not require the correction, the eleventh step is to add the corrected sample to an average. The second method further has the twelfth step of repeating for a number of measurements to create the average, then the thirteenth step of repeating for frequency A−, and A+. The second method further has the fourteenth decision step of whether the response to Frequency A is left of the peak or right of the peak. If, left of the peak, the frequency A is re-estimated higher, if right of the peak the frequency A is re-estimated lower. The second method further has the fourteenth decision step that if the output is substantially at the peak, then the second method is completed. This method determines the resonant frequency first of the magneto-mechanical pressure sensor <b>20</b> in the rotating environment of the tire <b>12</b>.

0100The disclosed method or algorithm reduces the number of measurements required for determining the resonant frequency is disclosed herein. The method preferably uses three features. First, the method uses a memory to suggest as a first estimate of resonant frequency (pressure), the last successfully measured resonant frequency. The second feature of the method is that the method takes advantage of the characteristic shape of the resonance curve to converge on the peak in fewer than <b>30</b> frequency guesses. These two features apply to both the temperature and pressure measurements. The third feature of this algorithm is that once temperature is determined, it compensates the search frequency for the pressure peak by the amount expected from the temperature measurement.

0101The initial estimate for resonant frequency is set to the last known resonant frequency. The response amplitude is measured. An offset to the estimated resonant frequency is added to and subtracted from the initial guess frequency. Referring to <figref idref="DRAWINGS">FIG. 14</figref>, there is shown a graph with “+” and “−” estimates. For example, if a peak had not shifted since the prior measurement, estimate A would still be at the peak and the neighboring frequency estimates would be A− and A+. Response amplitudes for the neighboring frequency estimates are also measured and temporally filtered. The relative amplitudes of the center and neighboring frequencies determine the position of the frequency triad on the resonance curve. An initial estimate that is still at the peak of the curve is detected when f(A−)<f(A)>f(A+), where f(A), f(A−) and f(A+) are the response amplitudes at the three frequencies. In a similar way, f(B−)<f(B)<f(B+), is indicative of the condition that the initial estimate was on the positive slope side of the resonance curve, and f(C−)>f(C)>f(C+) is indicative of the fact that the initial estimate was on the negative slope side of the resonance curve. Knowledge of relative position on the resonance curve is used to form the next estimated peak frequency. Successive iterations store all measurements of previous iterations for the measurement, and shift the frequency estimate intelligently so as not to repeat measurements made on previous iterations.

0102One skilled in the art should appreciate that simply knowing which way to move the peak frequency estimate can, reduce the number of measurements. In the usual situation in which temperature and pressure do not change since the last measurement, the peak frequency will be determined in one iteration of three measurements for about a ten fold improvement over a full successive frequency scan for a resolution of 30 frequency/pressure points.

0103In still another embodiment of the present invention, numerical solutions or optimization of nonlinear equations approximating the resonance curve function can be used to converge on the peak in a greatly reduced number of measurements. Using assumptions similar to those above for a successive interrogation frequency method, a single guess determination can be made in three frequencies×twenty five samples (to filter for a five-fold improvement of signal to noise ratio) or seventy five measurements. In one aspect in which pressure is not changing, a single predetermined guess will be accurate. Response times for the single predetermined guess measurements are about one-tenth those required in which all thirty pressures are measured. In contrast to the example cited above, at twenty miles per hour, pressure can be determined in fifteen seconds versus one hundred fifty seconds and at sixth miles per hour, pressure can be determined in five seconds versus fifty seconds.

0104Other embodiments of this method are possible in which a value of the slope is used to adjust the center frequency used for the next iteration estimate. It is evident from the shape of the resonance curve that the slope of the curve increases as the peak is approached. As discussed above, the sign of the slope will determine whether the next frequency guess should be higher or lower. A larger magnitude slope will suggest that the peak is near, and that the next frequency guess should be relatively closer.

0105Continuous methods for determining pressure from magnetomechanical sensors <b>20</b> in a tire pressure application are sensitive to a number of factors. Some factors include a strength of the magnetically hard material, a distance between the magnetically hard material and the magnetostrictive material, a temperature of the magnetostrictive material, loading of any mass on the surface of the magnetostrictive element. Still other factors are an ambient magnetic properties of the wheel, tire, or vehicle, a speed of the tire, in as much as it affects the centrifugal force on the magneto-mechanical pressure sensor, and therefore could affect the geometry of the sensor, thus affecting the resonant frequency of the magnetostrictive material. Other factors include shock, vibration, mechanical deformation and electrical noise.

0106The advantage of the continuous type sensor is that it will produce a signal related to all pressurization states in a continuous analog manner. Preferably, the present invention discloses a discrete sensor that overcomes these deficiencies in the art. In one preferred embodiment, the apparatus <b>10</b> preferably indicates whether the pressure is above or below a threshold value. In that context, discrete sensor designs described above differentiate between two pressurization states. Those discrete sensors might a) toggle between two resonant frequencies, or b) toggle between resonating and non-resonating states by application of a damping force to the magnetostrictive material. The concept can be extended to a plurality of discrete sensors yielding a multi-step capability. It is easily seen that by having a number of magneto-mechanical pressure sensors <b>20</b> each sensing whether the pressure is above or below its assigned threshold yields a sensing system that senses pressure to a resolution or sensitivity equal to the number of different discrete sensors used.

0107The electromagnetic excitation system <b>22</b> and receiver <b>24</b>, and the data interpretation system <b>26</b> preferably for single or multi-step systems is preferred over the continuous sensor design for its simplicity and reliability, primarily because fewer correction factors need to be applied. This method does not search for the resonant frequency peak as described above. Instead, the method recognizes oscillations from the magnetostrictive element at an expected resonant frequency range regardless of whether the peak resonant frequency has been shifted by the factors detailed above. The apparatus preferably detects a single resonating state of a magnetostrictive element, which responds to a single specified exciting frequency. Since this method intentionally operates on the shoulders of the resonant frequency curve, and not just at the peak, the design must assure that the response amplitude needs to be detectable over the expected range of resonant frequency peak shifts.

0108<figref idref="DRAWINGS">FIG. 15</figref> shows the design parameters to be considered for a discrete sensor. The resonance curve A represents the ideal resonance response of the discrete sensor. Curves B and C represent resonance curves for the maximum resonant frequency shifts expected for the effects detailed above. The vertical line D dropped down from the peak of the ideal resonance curve intersects curves Band C on the shoulders of their curves at points E and F, respectively. The abscissa values for points E and F represent the response amplitude of the sensor to the ideal resonant frequency for the shifted resonance situations. The horizontal line G represents a threshold amplitude for the detection circuitry. The vertical line D intersects all three curves, A, B, and C above the detection threshold.

0109Multi-step discrete sensor systems employ a plurality of magneto-mechanical sensors <b>20</b> with each operating at different ideal resonant frequencies. The ideal frequency of each component step sensor is chosen such that the response to the ideal resonant frequency for a given step sensor is detectable over the range of expected resonant frequency shifts due to temperature and pressure. Each ideal resonant frequency is offset enough that other alternate step sensors' responses to that frequency, for the expected range of resonance shifts due to temperature and pressure, are below detection threshold. The ideal frequencies of the individual discrete step sensors can be selected by a number of methods know to those skilled in the art. The resonant frequency is related to the length of the magnetostrictive material as discussed. Individual sensors may be cut to different lengths affecting the offsets in resonant frequency.

0110Alternatively, the magnetostrictive elements of each discrete step are all the same length, and the shift in ideal resonant frequency is effected by the strength of the non alternating biasing magnetic field. If this biasing field for each step magneto-mechanical pressure sensor is implemented by the magnetically hard element <b>34</b>, different field strengths may be realized by varying the distance of between the equally magnetically hard elements and magnetostrictive elements <b>38</b>, by varying the strength of the magnetically hard elements using uniform spacing, or a combination approach.

0111In still yet another embodiment of the multi-step discrete magento-mechanical pressure sensor <b>20</b> design, each sensor operates at the same resonant frequency range in an on/off manner. Preferably, each sensor <b>20</b> begins to resonate when its individual pressure threshold is exceeded. The thresholds of the individual sensors are staircased in an increasing way such that a data interpretation algorithm of the data interpretation system <b>26</b> can infer the pressure by simply counting the number of resonant peaks detected per revolution of the tire <b>12</b>.

0112It should be understood that the foregoing description is only illustrative of the present invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variances.