Abstract:
An apparatus and method are described for extracting useful work from pressure transients in a pneumatic tire to replace lost air from the tire. The apparatus and method operate continuously and without human intervention. When also used with a pressure relief valve, the apparatus and method permit the tires that are being driven to be maintained at a desired average pressure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/263,759, filed Nov. 23, 2009, the entire contents of which are hereby incorporated by reference herein and made part of this specification. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention generally relates to a method and apparatus for maintaining the proper pressure in a pneumatic tire, and more particularly to a method and apparatus for automatically having the tire pressure maintained while driving and without driver intervention or care. 
         [0004]    2. Discussion of the Background 
         [0005]    Pneumatic tires provide low rolling resistance and a high degree of maneuverability when the proper air pressure is maintained. All tires tend to lose air over time, and it is left to the driver or maintenance personnel to ensure that vehicle tires are inflated to the proper pressure. As a result, many cars and trucks are actually found to be operating with tires which are under-inflated, a condition that affects vehicle drivability, safety, and fuel economy. There exists a need in the art for a method and apparatus that can automatically maintain a proper air pressure within a tire. The apparatus should be economical and be easy to use with existing wheels, rims and tires, and be operable without maintenance, adjustment, power source, or connection to any external systems. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    The present invention overcomes the disadvantages of prior art by providing a device and method for providing air to tires without human intervention. By maintaining correct tire pressure, the use of the invention will reduce the safety hazards associated with driving on under-inflated tires, which include the possibility of blow-out and loss of control. Further, the use of the invention may promote increased tire operating lifetime and reduced rolling resistance, which will help to prevent unnecessary fuel consumption. 
         [0007]    In certain embodiments, a method is provided to inject air into tires as a natural consequence of driving. The injection of air may compensate for loss of pressure due to leakage and will allow the tire to be maintained at its optimal working pressure. 
         [0008]    In certain other embodiments, an apparatus is provided that automatically injects air into tires as a natural consequence of driving activity without any intervention by the vehicle owner or operator. In an alternative embodiment, when the air pressure in the tire reaches a set-point, a pressure-controlling valve may release excess air, preventing over inflating of the tire. 
         [0009]    In certain other embodiments, an apparatus may be installed inside the tire or incorporated into the wheel, and therefore be protected against contamination, impacts, or tampering. 
         [0010]    In certain embodiments, an apparatus is incorporated as an integral part of a manufactured wheel and thus will work with any tire subsequently fitted to the wheel. 
         [0011]    In certain embodiments, a device for a pressurizing the interior of a pneumatic tire of a vehicle is provided, where the interior tire pressure undergoes transients of pressure during operation of the vehicle. The device includes a pump that utilizes internal pressure transients to pressurize ambient air and provide the pressurized air to the interior of the tire. 
         [0012]    In certain other embodiments, a device for a pressurizing the interior of a pneumatic tire of a vehicle is provided, where the interior tire pressure undergoes transients of pressure during operation of the vehicle. The device includes a pump that utilizes internal pressure transients to pressurize ambient air and provide the pressurized air to the interior of the tire. The pump includes a first chamber having a variable internal volume with an inlet including a first one-way valve configured to accept ambient air into the chamber volume and an outlet including a second one-way valve configured to provide air from the chamber volume into the interior. The pump also includes a second chamber having a variable internal volume, where the second chamber includes a diaphragm in communication with the interior pressure and configured to transmit high interior pressure forces to pressurize air within the first chamber. The transients in the interior pressure provide pressurized air to the tire. 
         [0013]    In yet other certain embodiments, a method is provided for of providing air to a pneumatic tire having an average pressure, where the tire experiences pressure transients. The method includes operating a pump in constant communication with the interior of the tire, where the operating includes extracting work from the pressure transients to provide ambient air into the tire. 
         [0014]    These features together with the various ancillary provisions and features which will become apparent to those skilled in the art from the following detailed description, are attained by the method and apparatus of the present invention, preferred embodiments thereof being shown with reference to the incorporated drawings, by way of example, wherein: 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0015]      FIG. 1  is a cross-sectional view of a pneumatic tire including a pump installed in the valve stem; 
           [0016]      FIG. 2  is a schematic of a first embodiment pump as installed within a tire cavity; 
           [0017]      FIG. 3  is a schematic of a second embodiment pump as installed outside of a tire cavity; and 
           [0018]      FIG. 4  illustrate a method of using pump embodiments, where  FIG. 4A  illustrates a rest state for pump,  FIGS. 4B and 4C  illustrate consecutive states during pumping, and  FIG. 4D  illustrates the recovery of the pump. 
       
    
    
       [0019]    Reference symbols are used in the Figures to indicate certain components, aspects or features shown therein, with reference symbols common to more than one Figure indicating like components, aspects or features shown therein. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    Embodiments described herein include a pump that may be used to extract useful work from pressure transients within a pneumatic tire. Certain embodiments include, but are not limited to, impulse-driven diaphragm pumps. These pressure transients may occur, for example, when the vehicle on which the tires are mounted passes over bumps in the road as a natural consequence of driving. Thus, for example, one side of a diaphragm is exposed to the instantaneous pressure in the tire cavity, and the other side of the diaphragm is maintained at an average pressure. When the transient exceeds the average pressure, the pump may extract useful work from the gas. Certain embodiments described herein include a miniature diaphragm pump that provides air into a pneumatic tire of a vehicle, where a force for driving the pump, and thus inflating the tire, is obtained from tire pressure transients that result from the vehicle passing over bumps in the road. 
         [0021]    Embodiments of the present invention include a pump installed through the wall or rim of a tire. Thus, for example and without limitation, certain embodiments provide a pump placed through the wheel of a pneumatic tire. Other certain embodiments provide a pump placed through the rubber portion of the tire. The pump may be on the inside of the tire, on outside of the tire, or partially or completely within the wall of the tire. Certain other embodiments provide the pump within a valve stem. For example and without limitation,  FIG. 1  is a cross-sectional view of a pneumatic tire  1  having an interior tire cavity volume  4  in an ambient environment  5 . Tire  1  is installed on a wheel rim  3  and includes a pump  10  installed in a valve stem  105 . In various embodiments, pump  10  may be located within volume  4 , on the outside of tire  1  in ambient environment  5 , within valve stem  105 , or within tire  1  or rim  3 . 
         [0022]      FIG. 2  is a schematic of a first embodiment pump  10  as installed within a tire cavity  4 . For illustrative purposes, a portion of the wall or wheel of the tire is shown as tire T. As shown in  FIG. 2 , pump  10  includes an air inlet  100 , an outer housing  101 , a threaded mounting stem  105 , a first one-way valve  110 , a second one-way valve  111 , a first chamber  142 , a first diaphragm  140 , a second chamber  120 , a second diaphragm  130  having an opening  160 , a coupling rod  135 , a sintered insert  125 , a spring  150 , an opening  160 , and a cover  170  having an opening  171 . One-way valves  110  and  120  are configured to provide a flow of air from the exterior of the tire to the interior of the tire. 
         [0023]    In one embodiment, air inlet  100  is in fluid communication with ambient air of environment  5 , and opening  171  is in fluid communication with volume  4 . A cap (not shown) may be present to prevent the ingress of dust, mud, or other contamination from entering pump  10 . 
         [0024]    First chamber  142  is bounded by housing  101 , first diaphragm  140 , first one-way valve  110  and second one-way valve  111 . Second chamber  120  is bounded by housing  101 , first diaphragm  140 , second one-way valve  111 , second diaphragm  130 , and coupling rod  135  which connects the first and second one-way valves and has sintered insert  125  to provided restricted fluid communication between the second chamber and the interior of tire T, and thus allow the pressure within chamber  120  to be approximately the average tire pressure. Spring  150 , located between housing  101  and second diaphragm  130 , provides a restoring force for the second diaphragm after a pump stroke. Cover  170  provides mechanical protection to diaphragm  130 . 
         [0025]    Threaded mounting stem  105  is used for affixing the assembly inside the tire cavity. Stem  105  may pass, for example, through the wheel wall of tire T such that inlet  100  is exposed to the outside ambient air. One-way valves  110  and valve  111  permit ambient air flow into pump  10 . Sintered insert  125  permits the very slow equilibration of air pressure between chamber  120  and the tire cavity, permitting the permeation of air through it, with a high resistance to flow. Chamber  120  is thus maintained at a pressure equal to the long-term average of the tire cavity pressure. 
         [0026]    In certain embodiments, the volume of second chamber  120  is larger than the volume of first chamber  142 . First chamber  142  confines a small volume of air between one-way valves  110  and  111 . First diaphragm  140  is connected to second diaphragm  130  through coupling rod  135 , and thus motion of the second diaphragm towards the first diaphragm and the action of one-way valves  110  and  111  compresses air within first chamber  142  and will provide the compressed air into tire T. Diaphragm  130  is preferably constructed from a lightweight metal sheet attached to a flexible metal seal around the perimeter and then to housing  101 . 
         [0027]      FIG. 3  is a schematic of a second embodiment pump  10  as installed outside of a tire cavity. Pump  10  of  FIG. 3  is generally similar to the pump of  FIG. 2 , except as further detailed below. Where possible, similar elements are identified with identical reference numerals in the depiction of the embodiments of  FIGS. 1 ,  2  and  3 . 
         [0028]    Pump  10  of  FIG. 3  is intended installation on the wheel outside the cavity of tire T, and includes a mechanical connection  106  to a passage leading to the tire cavity, and opening  175  provides pumped air which is injected into the tire. Front cover  170  is a mechanical part of housing  101  and is strong enough to withstand the tire pressure. 
         [0029]    In an alternative embodiment, chamber  120  of  FIG. 2  or  FIG. 3  may not include insert  125  and is sealed permanently at a predetermined desired average tire pressure. 
         [0030]    The following is an example of the use of pump  10  to replace air which naturally leaks from a pneumatic tire over time. In general, pump  10  includes two coupled diaphragms, such as diaphragms  130  and  140 , which amplify pressure transients in the tire to pump ambient air into the tire. More specifically, transient pressures resulting from driving over bumps in the road under normal conditions will result in transient pressures which may be used to pump air into the tire. In certain embodiments, chamber  120  is maintained at the average tire pressure by permitting only a very restricted communication of air to the cavity volume through sintered insert  125 , which may be a sintered insert or similar device of microscopic porosity and thus presents a high-impedance path to air flow. Insert  125  thus allows the gradual equilibration of air between the tire and chamber  120  over time periods greater than the pressure transients, but less than the time over significant pressure is lost from the tire. The time period for equilibration may thus be on the order of hours or days. 
         [0031]    Diaphragm  130  is in fluid communication with the interior of the tire, and experiences transients in tire pressure. The coupling of the relatively larger diaphragm  130  to the smaller diaphragm  140  amplifies the pressure, resulting in a higher pressure in chamber  142 , which may then be injected in to the tire through one-way valve  111 . Once the air passes through one-way valve  111  and diaphragm  130  moves towards the original position, the pressure in chamber  142  drops below atmospheric pressure, one-way valve  111  closes and one-way valve  110  opens, refilling chamber  142  with ambient air. 
         [0032]    As described herein, pump  10  may be operated from transient pressures in the tire. As a example of the use of pump  10 , assume that each time the vehicle passes over a bump in the road, the tire pressure experiences a transient increase of pressure due to the compression of the rubber, increasing in pressure from a pressure P(tire) to a pressure {P(tire)+ΔP} where the transient increase is ΔP. If the pressure inside of chamber  120  is the average tire pressure P(tire), then the pressure difference of ΔP acting on the area of diaphragm  130  creates a force. The force will displace diaphragm  130  which, through the coupling action coupling rod  135  will displace diaphragm  140 , thus increasing the pressure of air within chamber  142 . 
         [0033]    The following examples are illustrate designs and uses of pump  10 , and are not meant to limit the scope of the present invention. A typical automobile tire contains approximately 30 liters of air at STP (standard temperature and atmospheric pressure), and at a pressure of 30 psig. It is not unreasonable that approximately 3% of the volume escapes from the tire per month, resulting in a loss of approximately 1 liter of air and 1 psi of tire pressure. Larger pumps may be designed for use in larger tires, as are used on trucks and heavy equipment. 
         [0034]    As a numerical example, if the tire rubber is temporarily displaced inwards by 1 cm over a contact footprint of 30 cm 2 , the tire cavity volume will be decreased by 0.3%, with a resulting instantaneous pressure increase of approximately ΔP=0.1 psig over a substantial area of diaphragm  130 . If the tire encounters a bump in the road every 100 feet, there will be on the order of 30 pump strokes per mile. In 1000 miles of driving there will be 30,000 pump strokes. If each pump stroke injects 30 cubic millimeters of air, this will create a total injection of total 1 liter of air pumped into the tire. 
         [0035]    Pump  10  may be sealed, with only one small hole on the inner tire cavity side, and one on the outer air-inlet side. Pump  10  may, for example, be threaded into a hole either inside the tire, or on the outside rim. Installation inside the tire cavity would reduce exposure to weather, dirt, mechanical impact and tampering. The assembly could also be manufactured as an integrated unit to be incorporated into the structure of a wheel, communicating with the tire cavity through an air passage. In this way, the assembly could be located at a smaller radius of rotation, leading to less centrifugal force acting on the components. 
         [0036]      FIGS. 4A-4D  illustrate the use of pump  10  to provide air to a tire resulting from pressure transients, where  FIG. 4A  is a rest state for pump  10 ,  FIG. 4B  shows the compression of air in sealed chamber,  FIG. 4C  shows the pumping of the compressed air into the tire, and  FIG. 4D  shows an intake of ambient air after pumping. 
         [0037]    In  FIGS. 4A-4D , the pressure within chamber  130  is the average tire pressure, P(ave), where  FIG. 4A  illustrates a rest state for pump  10 ,  FIGS. 4B and 4C  illustrate consecutive states during pumping, and  FIG. 4D  illustrates the recovery of the pump. The tire pressure P(tire) is illustrated as varying from the average tire pressure of P(ave) in  FIG. 4A  to an increased pressure P(tire)={P(ave)+ΔP} in  FIGS. 4B and 4C , back to the average pressure in  FIG. 4D . 
         [0038]    More specifically, in  FIG. 4A , the tire pressure P(tire) is at the average tire pressure of P(ave), and one-way valves  110  and  111  are closed. In  FIG. 4B , a pressure transient in the tire to P(tire)={P(ave)+ΔP} results in a pressure differential of ΔP acting on diaphragm  130 . The resulting displacement of diaphragm  130  is coupled to diaphragm  140  through coupling rod  135 . One-way valves  110  and  111  remain closed, and the pressure within chamber  142  increases. 
         [0039]    In  FIG. 4C , diaphragm  130  is displaced further. Eventually, the pressure within chamber  142  increases from atmospheric pressure to a pressure greater than P(tire)={P(ave)+ΔP}. One-way valve  111  then opens, as illustrated in  FIG. 4C , and air is pumped into the tire. 
         [0040]    In  FIG. 4D , the tire pressure has returned to P(tire)=P(ave). Spring  150  forces diaphragm  130  back to the position shown in  FIG. 4A . One-way valve  111  closes and, when the pressure within chamber  142  drops below ambient pressure, one-way valve  110  opens, drawing in ambient air. When the next pressure transient occurs in the tire, the cycle then repeats from the configuration shown in  FIG. 4A . 
         [0041]    Pump  10 , or a device having equivalent functionality, enable the use of transient pressure impulses generated by the passage of the tire over a naturally-occurring road bump, to inject a small volume of outside air into the tire cavity each time the wheel passes over a bump. Although each injection amount is small, this action repeated over many thousands of impulses will inject sufficient air into the tire to overcome gradual loss of pressure. 
         [0042]    A separate device (not shown) essentially of the form of a pressure-regulating tire inflation valve stem, may release excess pressure once the desired working pressure has been achieved. In this way, considerations of specific pressure settings do not have to be incorporated into the design of the automatic inflator. 
         [0043]    Reference throughout this specification to “certain embodiments,” “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments. 
         [0044]    Similarly, it should be appreciated that in the above description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment of this invention. 
         [0045]    Thus, while there has been described what is believed to be the preferred embodiments of the invention, those skilled in the art will recognize that other and further modifications may be made thereto without departing from the spirit of the invention, and it is intended to claim all such changes and modifications as fall within the scope of the invention. For example, any formulas given above are merely representative of procedures that may be used. Functionality may be added or deleted from the block diagrams and operations may be interchanged among functional blocks. Steps may be added or deleted to methods described within the scope of the present invention.