Abstract:
An apparatus to scavenge energy caused by changes in interior pressure of a container, including at least one flexible chamber containing a fluid at a predetermined pressure; a piezoelectric element coupled to the flexible chamber so as to generate electricity when the flexible chamber is flexed by a change in interior pressure of the container.

Description:
BACKGROUND 
   This invention relates to methods and apparatus for scavenging and using energy caused by changes in pressure. This includes but is not limited to using changes of pressure in closed or substantially closed atmosphere environments to create electrical energy which is then used as a power source. 
   The invention will be described in reference to pneumatic devices and in particular pneumatic tires used in vehicles. However, this description is one exemplary embodiment of the invention and systems and methods of the invention are applicable to any circumstance where changes in pressure occur at a frequency that they may be used to convert mechanical energy to electrical energy. 
   Tire safety studies show that maintaining proper tire pressure improves vehicle handling, improves fuel economy, increases tire life and helps avoid accidents. An NHTSA research survey of U.S. passenger vehicles found that 27% of passenger cars on U.S. roadways were driven with one or more substantially under-inflated tire. The survey found that 33% of light trucks (including sport utility vehicles, vans and pickup trucks) are driven with one or more substantially under-inflated tire. Other studies have shown that nearly 20% of service stations providing customers with tire pressure gauges on their air pumps use gauges that over report the pressure present in a tire by at least 4 psi (pounds per square inch) or more. At pressure levels that are typical for most passenger cars or SUVs, nearly 10% of service station air pump gauges over report by 6 psi or more. In addition, radial tires can lose much of their tire air pressure and still appear to be fully inflated. 
   In response to this safety issue, the federal government has enacted standards which require motor vehicles to become equipped with tire pressure monitoring systems. The standards specify performance requirements for tire pressure monitoring systems to prevent significant under-inflation of tires and the resulting safety problems. The standard applies to passenger cars, multipurpose passenger vehicles, trucks and buses that have a gross vehicle weight rated of 10,000 pounds or less. The tire pressure monitoring system refers to a system that detects when one or more of the vehicles tires are under-inflated and illuminates a low tire pressure warning telltale. The low tire pressure warning telltale must be mounted inside the occupant compartment in front of and in clear view of the driver. The tire pressure monitoring system must continue to meet the requirements of the standard when the vehicle&#39;s original tires are replaced with tires of any optional or replacement size. 
   Related art tire pressure monitoring systems provide vehicles using pneumatic tires with a system having a sensor to sense conditions of a tire. See U.S. Pat. Nos. 6,438,193 and 6,518,877 which are hereby incorporated by reference. The conditions may include internal pressure, temperature, number of revolutions, etc. Related art systems are mounted in the tire and include a transmitter which communicates sensed data to a receiver located in the vehicle. The sensed data may then be communicated to the vehicle operator via a user interface, such as a display. The related art systems are often powered by batteries which wear out and need to be replaced. This increases labor costs and hazardous waste. This may also result in system failures due to lack of power during the operation of the vehicle. 
   SUMMARY 
   The invention provides a power supply by providing methods and systems that convert mechanical energy to electric energy and in particular the changes in pressure of a rotating tire into electric energy, which is then stored and used to power the tire based components of a tire pressure monitoring system. As a tire rotates, turns and otherwise trundles down a road, its internal volume is constantly changing causing variations of pressure inside the tire. These pressure fluctuations can be used to cause mechanical changes in a mechanical portion which are transmitted to a piezoelectric element. The piezoelectric element is distorted by the mechanical changes and generates electrical energy. The electrical energy is stored and delivered to the tire mounted portion of the tire pressure monitoring system via an electric circuit. 
   In an exemplary embodiment of the invention, an aneroid cell is the mechanical portion of the system and is linked to a piezoelectric element so that mechanical changes in the aneroid cell cause mechanical changes in the piezoelectric element. 
   In another exemplary embodiment of the invention, a bourdon tube is the mechanical portion of the system and is linked to a piezoelectric element so that mechanical changes in the bourdon tube cause mechanical changes in. the piezoelectric element. 
   In another exemplary embodiment of the invention the piezoelectric element is formed to surround the mechanical portion so that mechanical changes in the mechanical portion are directly transmitted to the piezoelectric element. 
   In another exemplary embodiment of the invention the piezoelectric element is linked mechanically to the mechanical portion so that mechanical changes in the mechanical portion are transmitted through the mechanism linkages to the piezoelectric element. 
   In another exemplary embodiment of the invention, the various exemplary embodiments of the invention are mounted on a valve stem. 
   In another exemplary embodiment of the invention, electrical energy created by the piezoelectric element is stored in a capacitor. 
   In another exemplary embodiment of the invention, electrical energy created by the piezoelectric element is stored in a battery. 
   In another exemplary embodiment of the invention, the tire pressure monitoring system includes a sensor that senses at least one of tire pressure, tire temperature and tire revolutions. 
   In another exemplary embodiment of the invention, data sensed by the sensor is transmitted to a receiver and the data received by the receiver is communicated to the user via a user interface. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic of an apparatus for scavenging and using energy caused by changes in pressure according to one exemplary embodiment of the invention; 
       FIGS. 2A–2C  are schematics of an aneroid chamber used as the pressure reactor according to an exemplary embodiment of the invention; 
       FIGS. 3A–3C  are schematics of a bourdon tube used as a pressure reactor according to an exemplary embodiment of the invention; 
       FIG. 4  is a schematic of a method of mounting an apparatus for scavenging and using energy caused by changes by pressure according to an exemplary aspect of the invention; and 
       FIGS. 5A and 5B  are schematics of a sensed data receiver and transmitter according to an exemplary aspect of the invention. 
   

   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     FIG. 1  is a schematic of an exemplary embodiment of the invention using a aneroid chamber as the mechanical portion.  FIG. 4  is a schematic of the exemplary embodiment of  FIG. 1  mounted on the valve stem of a pneumatic tire. However, it should be appreciated that any environment with sufficient changes in pressure over a sufficient time period would be suitable to create the mechanical changes in the mechanical portion necessary to satisfy the requirements of the exemplary embodiments of the invention. 
   As the tire trundles down the road, interior pressure P 2  is constantly changing. The changes in pressure ΔP are communicated to the aneroid chamber  18  via the interim atmosphere of the pneumatic tire  11 . The aneroid chamber  18  is a tightly sealed chamber or series of chambers containing air at a predetermined pressure. The pressure P 1  of the aneroid chamber may be matched to the manufacturers recommended cold inflation pressure of the tire. Aneroid chambers are well-known to detect changes in atmospheric pressure. They may be formed from any suitable material, such as stainless steel or brass. The piezoelectric element  20  is placed in relation to the aneroid chamber  18  so that expansions or contractions of the aneroid chamber  18  caused by changes in air pressure P 2  inside the tire  11  cause mechanical changes in the piezoelectric element  20  thus generating electrical energy. The use of piezoelectric elements is well-known. See U.S. Pat. No. 6,438,193 which is hereby incorporated by reference. 
     FIGS. 2A–2C  are schematics showing the effects of the changes of pressure P 2  on the aneroid chamber  18 . It should be appreciated that  FIGS. 2A–2C  are not drawn to scale and features are exaggerated for representation and explanation purposes. 
     FIG. 2A  shows an aneroid chamber  18 . In the wall  18 A of the aneroid chamber  18 , there are formed circular corrugations  19 . The corrugations are formed in any suitable size, number and shape to make the wall  18 A flexible to provide a desired mechanical change in the shape of the aneroid chamber  18  when subjected to changes in pressure P 2 . It should be appreciated that the corrugations  19  are optional. Furthermore, it should be appreciated that the aneroid chamber  18  may be any suitable size or shape so long as the aneroid chamber  18  is able to be influenced mechanically by the changes in pressure P 2 . 
   In  FIG. 2A , the pressure P 1  is equal to pressure P 2 . There are no mechanical changes in the aneroid chamber  18 . Thus, the piezoelectric element  20  does not experience any mechanical changes and no electricity is generated. 
     FIGS. 2A–2C  show an exemplary embodiment of the invention where the piezoelectric element  30  is formed to surround the aneroid chamber  20 . However, it should be appreciated the various exemplary embodiments of the invention include forming or positioning a piezoelectric element in any suitable relationship such that mechanical changes caused by changes in pressure P 2  cause mechanical changes in the piezoelectric element  20 . For example, it is well known to transmit mechanical changes in aneroid chambers using mechanical linkages. 
   In  FIG. 2B  the pressure P 1  is greater than P 2 . This causes the wall  18 A to deflect outward at those portions where the corrugations  19  are formed. The deflection of the wall  18 A causes a similar deflection in the piezoelectric element  20 . Thus, electrical energy is generated. Similarly,  FIG. 2C  shows the result when the pressure P 1  is less than P 2 . This causes the wall  18 A to deflect outward at those portions where the corrugations are formed. The deflection of the wall  18 A causes a similar deflection in the piezoelectric element  20 . Thus, electricity is generated. 
     FIGS. 3A–3C  are schematics of an exemplary embodiment of the invention using a bourdon tube  30  as the pressure reactor. 
     FIG. 3A  is a schematic of a C-shaped bourdon tube  30 . The bourdon tube  30  has a hollow elliptical cross section as shown in  FIG. 3B . One end  30 A of the bourdon tube  30  is closed. The other end  30 B is open to the pressure P 2 . The walls  30 C are thin and change shape when there are changes in pressure P 2 . The open end  30 B is fixed. Thus, changes in pressure P 2  cause changes in the position of the closed end  30 A. The tube  30  is formed to be bent into an arc of a circle generally between 270 to 300 degrees. When pressure P 2  is increased, the cross section becomes more circular as shown in  FIG. 3C . This causes the tube to straighten out until the force of the fluid pressure is balanced by the elastic resistance of the tube  30 . 
   A piezoelectric element  20  is put in mechanical relation through the use of well known mechanical linking elements to either the tube walls or the closed end of the tube, so that changes in the shape or position of either will cause mechanical changes to the piezoelectric element and electricity is generated. The piezoelectric element  20  may be placed in any suitable relationship to the bourdon tube  30  to transfer the mechanical change.  FIG. 3A  shows a mechanical linkage  32 . Mechanical linkages for transferring mechanical changes of bourdon tubes are well known.  FIGS. 3B and 3C  show a configuration where the piezoelectric element  20  is formed to surround the bourdon tube  20 . 
   The electrical energy generated by the piezoelectric element  20  is ac. The energy is conditioned by the rectifier  25  and the regulator  26  to convert the ac signals to a stable DC power supply. The power supply is stored in storage  26  and used to supply power to sensor  27 , digital circuit  28  and transmitter  29 . Storage  26  may be any suitable electricity storage device such as a capacitor on battery. The digital circuit processes the sensor signals and communicates with the transmitter  29  which conditions the signals generated by the sensors  27  for transmission and broadcasts a signal representative of at least one of the vehicle tire parameters being monitored via antenna  42 . The broadcast signal is received by antenna  44  which is in communication with receiver  40 . The receiver  46  processes the received signal which is then communicated to a user through a user interface, such as a display or an audio warning system. 
   In the exemplary embodiment of  FIG. 4  the apparatus of an exemplary embodiment of the invention is mounted on valve stem  40  which in turn is mounted on a tire rim  10  on pneumatic tire  11 . It should be appreciated that the apparatus of an exemplary embodiment of the invention may be formed integrally with the valve stem  40  to facilitate mounting during vehicle manufacture or when new tires are mounted. Alternatively, the apparatus of an exemplary embodiment of the invention may be formed to be mounted on the valve system  40  by any suitable means such as threads, clips, etc. It should further be appreciated that the apparatus of an exemplary embodiment of the invention may be mounted in any suitable location so long that the pressure changes of the environment create mechanical changes in the apparatus of the exemplary embodiments of the invention. 
   In the exemplary embodiment of  FIG. 4  a housing  12  is provided to enclose the apparatus. The housing  12  may be formed of any suitable material to provide protection during handling, installation and use of the apparatus of the exemplary embodiment of the invention. The housing  12  includes inlets  14  and vents  16  to allow the pressure changes of the interior of the tire to reach the mechanical portion. 
   In various exemplary embodiments of the invention, the mechanical portion may also be used as a pressure sensor. 
   While the invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the exemplary embodiments or constructions. While the various elements of the exemplary embodiments are shown in various combinations and configurations, which are exemplary, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the invention.