Patent Application
20080084138
a) and 3(b) are idealized cross-section diagrams of portions of a tire that can be used with the present invention.
a)-(d) depicts several examples of a piezoelectric layer that can be used with the present invention.
Layer 101 is formed of a piezoelectric material capable of generating an electrical voltage when subjected to an appropriate force and includes electrodes formed on the piezoelectric material for carrying a current caused by that voltage to the conversion circuit 102. In one embodiment, layer 101 is formed of flexible lead zirconate titanate fiber composites, manufactured using a suspension spinning process. Such piezoelectric material is commercially available from Advanced Ceramatics, Inc. of Lambertville, N.J. The spinning process is well known in the art, as described in U.S. Pat. No. 5,827,797 to Cass et al, the entire contents of which is hereby incorporated by reference for the purpose of including all of its contents. (The inventor understand that the National Aeronautics and Space Administration has also developed a flexible lead zirconate titanate fiber composite, called Flex Patch, used on space craft exteriors and aircraft wings to harvest power from vibration energy. It is not known whether Flex Patch is commercially available or what manufacturing process is used to create it.) For purposes here, lead zirconate titanate will be referred to as PZT. The invention, however, is not limited to use of PZT as a piezoelectric, except as expressly set out in the claims. Other piezoelectric materials, such as polyvinylidene flouride, otherwise known as PVDF, may also be used. PVDF is available commercially from many sources and is sold under the trade names KYNAR® and KYNAR FLEX® by Arkema, Inc. of Philadelphia, Pa. Piezoelectric layer 101 is described in more detail below.
In some embodiments layer 101 may also be encased in a layer of protective rubber or some other material (not shown) in order to increase durability or, in embodiments as those described below, to hold the various portions of layer 101 together. Piezoelectric layer 101 may also include multiple sub-layers of piezoelectric material, electrically connected together, in order to form a piezoelectric “stack”. The sub-layers of such a stack may be connected in parallel to a load, or in series. Piezoelectric layer 101 is described in more detail below.
When the automobile is in motion the weight of the automobile exerts a force downward on the tires of the automobile, and also on the portion of the piezoelectric layer closest to the ground, generating a piezoelectric voltage that drives a current through the conversion circuit. Piezoelectric materials create a piezoelectric voltage only when a force is applied or removed; they do not create a constant voltage while the force is unchanging. Thus, if the automobile is at rest no useful piezoelectric voltage will be created. However, as the automobile moves the tire turns, exposing a different portion of layer 101 to the force created by the weight of the automobile and removing that force from the portion of layer 101 that was previously under the weight of the automobile. While the automobile is in motion layer 101 therefore creates a series of electrical pulses that push current through the electrodes to the conversion circuit 102.
Conversion circuit 102 receives the electrical pulses from layer 101 and converts them into a form suitable for transmission to battery 103 and storage therein. Specifically, one example of a suitable conversion circuit would include a diode-based full-wave rectifier circuit in parallel with a filter capacitor (or capacitors) and a DC-DC converter. The rectifier converts the pulses received from the piezoelectric layer to a generally DC current, which the filter capacitor smooths out. The DC-DC converter than converts the DC current into a form appropriate for the battery.
Referring now to
Conversion circuitry 102 is shown as comprising a rectifier 203, a filter capacitor C1 and a DC-DC converter 204, all connected in parallel and configured to convert the power delivered from the coupler to a form more suitable for storage in the battery 103. Alternatively, power from the converter may be transmitted directly to the engine/motor of the automobile, without first being stored in the battery. Those of ordinary skill in the art will understand that, in such an embodiment, the conversion circuit must be configured to that the electrical power output from it is in a form suitable to the input of the engine/motor.
a) depicts an idealized cross-section diagram of portions of a radial tire 300 that can be used with the present invention, from the perspective of a person facing the treads of the tire. Tire 300 is depicted as including layers 301-305, as well as piezoelectric layer 101. Layers 301 through 305 depict a radial plies, a first steel belt, a second steel belt, a cap plies and a tread layer, respectively. (Tread layer 305, for purposes of this application, will be characterized as “above” the cap plies layer 304 and first steel belt layer 302 will be characterized as “below” the tread layer 305. Put another way, the outermost layer will here be referred to as the “highest” layer and the innermost as the lowest.) These layers are conventional tire layers found in almost any commercially available radial tire. As is well known, radial tires usually include several other structures, such as liner, filler and beads, which are not necessary to the explanation of the invention, so will not be further described in detail. Other or different configurations of the tire are known and will therefore also not be further described. Indeed, the tire configurations depicted in
b) depicts a more specific example of a tire that may be used with the present invention. In this embodiment, piezoelectric layer 101 includes a sub-layer, or sub-layers, of piezoelectric material denoted 101(a), onto the upper and lower faces of which are formed electrodes 101(b). The electrodes may be formed of a metallic material such as phosphor bronze or brass. They may also be manually written onto the face of the piezoelectric material using silver or platinum paste. Other techniques and materials may also be used. The formation of electrodes on piezoelectric material is known to the art and will not be further described. The electrodes are connected to conductors 101(d) that are formed in the tire, preferably under the cap plies, and which lead to the coupling arrangement described in more detail below. A durable and flexible rubber material 101(c), made from for example a halobutyl rubber or a silicon rubber, may be formed around the piezoelectric material 101(a) and electrodes 101(b) to protect it. Electrodes 101(b) are electrically connected to conductors 101(d), which run over the should of the tire and along the inside of the side-wall of the tire to couple the electrodes to a power bus (not shown) formed, in this example, within the tire and above the radial plies.
c) is a different cross-sectional view of an exemplary tire portion similar to that of
The tire examples depicted in
This known process may be modified, however, consistent with the present invention as follows. A piezoelectric layer is formed. As noted herein, the layer includes one or more plates of piezoelectric materials, such as flexible PZT, to each of which has been attached electrodes. A stack of piezoelectric plates may also be employed. The piezoelectric layer must be formed into a shape that is appropriate for the tire into which it will be placed, similar to that of the steel belts for example. The plates must then be electrically connected by the interconnection of their electrodes, using additional electrical conductors if needed, depending on the configuration of the plates. In one embodiment the piezoelectric plates are then encased in a durable, flexible rubber as described above, while ensuring that the electrodes and/or electrical conductors are accessible. The piezoelectric layer is then placed in the tire-building machine in the position desired, for example, between the tread and cap plies on the “non-carcass” side of the machine. Alternatively, the piezoelectric layer may be placed between any other two layers on either the carcass or non-carcass side of the machine. The piezoelectric layer is next electrically connected to a power bus, to be described in more detail below, which couples the layer to, for example, the circuitry shown in
Referring now to
a) depicts layer 101 as a single plate of piezoelectric material of length and width sufficient to follow the contour and general circumference of the tire.
b) depicts layer 101 formed of multiple plates of piezoelectric material, each generally of the same width (that is, the vertical direction in the Figure) as the tire but of a much smaller length than the tire circumference. In this embodiment the plates are arranged in a manner so that together they form a layer substantially similar in shape to the layer depicted in
c) and (d) depicts yet another embodiment, in which layer 101 is formed of many smaller plates, having physical dimensions much smaller than those of the tire. As shown in
In this example, the piezoelectric plates are formed in such a manner that their native shape has a slight curvature and are placed within the tire so that the radius of the plate's curvature is in the same direction as the radius of the tire, as indicated. The formation of piezoelectric plates having a curvature is well-known in the art. See, for example, Kobayashi et al., Integrated Flexible High Temperature Ultrasonic Transducers, presented at the 4th International Workshop on Ultrasonic and Advanced Testing and Material Characterization in June of 2006 at U.Mass Dartmouth, Mass., the entire contents of which is hereby incorporated by reference for the purpose of including all of its contents. Utilizing plates with such a curvature increases the electrical charge developed in the piezoelectric material when a force is applied so as to flatten the plates (i.e., when the plates are between the ground surface and the weight of the automobile). It also helps prevent cracking of the piezoelectric material during normal use.
The reader should understand that the inventor does not intend for the description of the invention and several of its embodiments to limit the scope of the claims. To the extent any limitation of the rights sought is intended, they have been included in the express language of the claims.
