Patent Publication Number: US-10322611-B2

Title: System for an air maintenance tire assembly

Description:
FIELD OF THE INVENTION 
     The present invention relates to a system and method for maintaining appropriate air pressure within a pneumatic tire. More specifically, the present invention relates to a rim mounted system for directing air into a tire cavity of a pneumatic tire. 
     BACKGROUND OF THE INVENTION 
     Conventional pneumatic tires are designed to perform for relatively long periods of time. In many cases, automobile tires are now expected to have a useful service life of 30,000, 50,000, or 70,000 miles. However, even long-life pneumatic tires are subject to air pressure losses due to puncture by nails and other sharp objects, temperature changes, and/or diffusion of air through the tire itself. 
     Since air diffusion reduces tire pressure over time, the pneumatic tires are often continually underinflated. Accordingly, drivers must repeatedly act to maintain tire pressures or fuel economy, tire life, and/or vehicle braking and handling performance will be reduced. Tire Pressure Monitoring Systems (TPMS) have been proposed to warn drivers when tire pressure is significantly low. Such systems, however, remain dependent upon a driver taking remedial action, when warned, to re-inflate a tire to the recommended pressure. It is desirable, therefore, to incorporate an air maintenance feature within a pneumatic tire that will maintain recommended air pressure without requiring bothersome driver intervention. 
     SUMMARY OF THE INVENTION 
     A first system in accordance with the present invention is used with a pneumatic tire mounted on a wheel rim to keep a tire cavity of the pneumatic tire from becoming underinflated from a set pressure. The first system includes a plurality of pumps attached circumferentially to the wheel rim, each pump having a piston for inflating the tire cavity and a weight for moving the piston, and a stop mechanism for each pump, the stop mechanism including a stop piston, a stop cylinder, a first spring, and a second spring, when air pressure in the tire cavity reaches the set pressure, the set pressure overcomes a force of the first spring against the stop piston and moves the stop piston into a stopping engagement with the weight, when air pressure in the tire cavity is below the set pressure, the second spring overcomes the force of the first spring and moves the stop piston away from the weight. 
     According to another aspect of the first system, the first spring is disposed internally to the stop cylinder with the first spring engaging both an upper end of the stop cylinder and the stop piston. 
     According to still another aspect of the first system, the second spring is disposed internally to the stop cylinder with the second spring engaging both a lower end of the stop cylinder and the stop piston. 
     According to yet another aspect of the first system, the stop cylinder has a first port pneumatically connected to the tire cavity. 
     According to still another aspect of the first system, the stop cylinder has a second port pneumatically connected to ambient pressure conditions. 
     According to yet another aspect of the first system, the plurality of pumps and the control valve define a multi-chamber pump configuration. 
     According to still another aspect of the first system, two chambers within the pump are connected by a narrow passage having a one-way check valve. 
     According to yet another aspect of the first system, the plurality of pumps define a force control system with a maximum pumping capability determined by a piston of each pump moving a maximum distance within each pump. 
     According to still another aspect of the first system, each pump includes a first diaphragm limiting motion of a piston in a first direction and a second diaphragm limiting motion of the piston in a second opposite direction. 
     According to yet another aspect of the first system, pump parameters include a piston mass parameter, a first piston travel parameter, a second piston travel parameter, mass parameter of the weight. 
     A second system in accordance with the present invention models a pneumatic tire mounted on a wheel rim and a pumping mechanism mounted on the wheel rim to keep a tire cavity of the pneumatic tire from becoming underinflated from a set pressure. The second system includes a plurality of pumps attached circumferentially to the wheel rim, each pump having pump parameters, a control valve for controlling inlet air into a tire cavity of the pneumatic tire, the control valve having valve parameters, the system predicting system performance under various configurations and conditions through use of the pump parameters and the valve parameters; and a stop mechanism for each pump, the stop mechanism including a stop piston, a stop cylinder, a first spring, and a second spring. 
     According to another aspect of the second system, when air pressure in the tire cavity reaches the set pressure, the set pressure overcomes a force of the first spring against the stop piston and moves the stop piston into a stopping engagement with the weight. 
     According to still another aspect of the second system, when air pressure in the tire cavity is below the set pressure, the second spring overcomes the force of the first spring and moves the stop piston away from the weight. 
     According to yet another aspect of the second system, the plurality of pumps and the control valve define a multi-chamber pump configuration. 
     According to still another aspect of the second system, each stop cylinder of each stop mechanism includes two chambers on either side of the piston. 
     According to yet another aspect of the second system, each pump includes two chambers connected by a narrow passage having a one-way check valve. 
     According to still another aspect of the second system, the pumps are fit to the wheel rim; set P R (i)=P L (i)=P 0 , i=1 to n (total number of pumps used); set x(i)=0 and θ(i)=2π/n(i−1); P L (0)=P 0  (always) and P R (n+1)=P tire  (the tire cavity); calculate new x(i), P R (i) and P L (i); determine check valve status: if P R (i)≥P L (i)+Pcr, then check valve is open; if P L (i−1)≥P R (i)+Pcr, then adjacent check valve is open; balance pressure between connected chamber and reset check valve to close; and recalculate x(i), P R (i) and P L (i) until no more open check valve. 
     According to yet another aspect of the second system, subsequently, the wheel rim rotates to a predefined step angle; calculate new x(i), P R (i) and P L (i); determine check valve status: if P R (i)≥P L (i)+Pcr then check valve is open; if P L (i−1)≥P R (i)+Pcr then adjacent check valve is open; balance pressure between connected chamber and reset check valve to close; and recalculate x(i), P R (i) and P L (i) until no more open check valve. 
     According to still another aspect of the second system, the plurality of pumps define a force control system with a maximum pumping capability determined by a piston of each pump moving a maximum distance within each pump. 
     According to yet another aspect of the second system, the pump parameters include a piston mass parameter, a first piston travel parameter, a second piston travel parameter, and a mass parameter of the weight. 
    
    
     
       DETAILED DESCRIPTION OF DRAWINGS 
       The following drawings are illustrative of examples of the present invention. 
         FIG. 1  is a schematic representation of part of a system in accordance with the present invention. 
         FIG. 2  is a schematic representation of part of a system for use with the present invention. 
         FIG. 3  is a schematic representation of part of a system for use with the present invention. 
         FIG. 4  is a schematic representation of another part of the system of  FIG. 3 . 
         FIG. 5  is a schematic representation of another example system for use with the present invention. 
         FIG. 6  is a schematic representation of part of the example system of  FIG. 5 . 
         FIG. 7  is a schematic representation of part of still another example system for use with the present invention. 
         FIG. 8  is a schematic representation of another part of the example system of  FIG. 7 . 
         FIG. 9  is a schematic representation of still another part of the example system of  FIG. 7 . 
         FIG. 10  illustrates the piston mass effect on pumping capability and pumping pressure. 
         FIG. 11  illustrates the piston mass effect on pumping capability and pumping pressure. 
         FIG. 12  illustrates the number of pistons effect on pumping capability and pumping pressure. 
         FIG. 13  illustrates the number of pistons effect on pumping capability and pumping pressure. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLES OF THE PRESENT INVENTION 
     As shown in  FIGS. 3 through 9 , an example air maintenance tire system  10  for use with the present invention may provide a low profile and effective multi-chamber pump system that may easily mount inside of a wheel rim  12  with no significant modification to the wheel rim (minor modification may be required for air inlet having two stems). Further, the air maintenance tire system  10  requires no significant changes to tire/wheel assembly or tire/wheel performance. 
     The air maintenance tire  10  may include a pumping mechanism, pump driving mechanism, or pump  14 , utilizing gravitational force changes during rotation of the air maintenance tire. The pump driving mechanism  14  may include use of a mass of a piston body  16  moving against a pair of diaphragms  19  or an external mass (not shown) driving the piston body using a cam/gear system. If the mass of the piston body  16  is used, the pump driving mode may be based on force control. If a cam/gear system and external mass are used, gravitational force may drive gear rotation and convert this rotation to controllable displacement, as described in U.S. Publication No. 2015/0314657, System for an Air Maintenance Tire Assembly, herein incorporated by reference in its entirety. 
     As the tire/wheel rotates, the piston body  16  may travel in a forward direction and an opposite backward direction per each revolution thereby producing a high pumping frequency. Thus, higher vehicle speed may provide higher pumping frequency. The parameters of the pumping action depend upon the mass and angular velocity of the tire/wheel assembly. Tire load or other external conditions may not effect pumping action. 
     Due to an amplification effect, the compression of the pump driving mechanism  14  may be defined as:
 
 R =( r ) 2n  
 
     where 
     R: system compression ratio 
     r: single chamber compression ratio 
     n: number of pump in the system 
     Thus, a high compression ratio for each pump  18  is not necessary to achieve a high compression ratio (e.g., low force and/or deformation may produce high compression). 
     The pump driving mechanism  14  may include 4 to 10 pumps  18  and pump holders  20  may be configured linearly on a belt forming a loop and fitting circumferentially in a middle groove of the wheel rim  12  (radially innermost part of the wheel rim). A control valve  22  may be shaped similarly to the pumps  18  and may be placed in a space between the beginning and the end of the belt. Pump holders  20  may have adjustable lengths that fit any size of wheel rim  12 . 
     A passage connection from a first valve stem to the control valve inlet port may be connected after the belt is secured to wheel rim  12  ( FIG. 5 ). The control valve  22  may include a filter unit  30 . The pump driving mechanism  14  may be bi-directional and mounted in either direction. The control valve  22  may include an adjustment for varying a set pressure for the tire cavity. The pump driving mechanism  14  thus may have a low profile around the wheel rim  12  that in no way interferes with tire mount/dismount and provides clearance in the tire cavity for impacts incurred (cleat or pothole) during driving of the vehicle. Further, the 360° design ( FIG. 5 ) of the pump driving mechanism  14  may be a balanced construction in no way degrading the balance of the tire/wheel assembly. 
       FIG. 7  shows of an example configuration having four pumps  18 , six check valves  28 , a control valve  22 , and a filter  30 . This configuration may scale to n pumps  18  with the control valve  22  controlling air inlet into the configuration from outside of the tire  10 . The check valve  28  to the left of the control valve  22  in  FIG. 7  may be optional. 
       FIG. 8  shows of another example configuration having four pumps  18 , five check valves  28 , a control valve  22 , and a filter  30 . This configuration may scale to n pumps  18  with the control valve  22  controlling air outlet from the configuration to the tire cavity. The control valve  22  may be placed in a bypass of the pumps  18 . 
       FIG. 9  shows of still another example configuration having four pumps  18 , five six check valves  28 , a control valve  22 , and a filter  30 . This configuration may scale to n pumps  18  with the control valve  22  controlling air outlet from the configuration to the tire cavity. The control valve  22  may be placed in series with the n pumps  18 . 
     A pumping system, theory, or analytical model  100  for use with the present invention may define behavior of the multi-chamber pump system described above ( FIGS. 3-9 ). Such a system may be converted to suitable computer codes as an analytical pumping model. This model may design and predict system performance under various configurations and conditions for both consumer and commercial air maintenance tire systems. 
     There may be n pumps spaced equally about the circumference of the wheel rim  12 . Each pump  18  may include one piston  16  placed between two chambers  101 ,  102 , as described above ( FIG. 2 ). The two chambers  101 ,  102  may be connected by a narrow passage having the one-way valve  28 , or CV(i), with i=1 to n ( FIGS. 4-8 ). CV(n+1) and CV(n+2) may be placed at the air inlet and outlet of the system  10 , and between the pumps  18 , CV(i), i=1 to n. 
     For example ( FIG. 1 ): 
     Step 0
         Flow flat assembly to fit to rim ( FIGS. 5 &amp; 6 );   Set P R (i)=P L (i)=P 0 , i=1 to n (total number of pumps  18  used);   Set x(i)=0 and θ(i)=2π/n(i−1);   P L (0)=P 0  (always) and P R (n+1)=P tire  (the tire cavity);   Calculate new x(i), P R (i) and P L (i);   Determine check valve status:
           If P R (i)≥P L (i)+Pcr, then icv(i) is open;   If P L (i−1)≥P R (i)+Pcr, then icv(i−1) is open;   Balance pressure between connected chamber and reset check valve to close; and   Recalculate x(i), P R (i) and P L (i) until no more open check valve.   
               

     Step 1 to N
         Rotate wheel to a predefined step angle;   Calculate new x(i), P R (i) and P L (i);   Determine check valve status:
           If P R (i)≥P L (i)+Pcr then icv(i) is open;   If P L (i−1)≥P R (i)+Pcr then cv(i−1) is open;   Balance pressure between connected chamber and reset check valve to close; and   Recalculate x(i), P R (i) and P L (i) until no more open check valve.   
               

     The system  100  may also be exemplarily described: 
     
       
         
           
               
             
               
                   
               
             
            
               
                 Pump moved from θ to θ′ 
               
               
                 Force components ΔPA and mg cos(θ′) 
               
               
                 where ΔP = P L  − P R   
               
               
                 check force balance for piston movement 
               
               
                 If 
               
               
                 ΔPA + mg cos(θ′) − mrα &gt; 0 then piston moving to right 
               
               
                 ΔPA + mg cos(θ′) − mrα &lt; 0 then piston moving to left 
               
               
                 ΔPA + mg cos(θ′) − mrα = 0 then piston no movement 
               
               
                 x : current piston position relative to piston center (−x o  ≤ x ≤ x o ) 
               
               
                 calculate new piston x′ by using ΔP′A + mg cos(θ′) − mrα = 0 
               
               
                 where ΔP′ = P L ′ − P R ′ 
               
               
                   
               
               
                 
                   
                     
                       
                         
                           
                             
                               
                                 
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                 where 
               
               
                 l : chamber length at 0 position 
               
               
                 V d  : dead-end volume (imcompressible) of each chamber 
               
               
                 α : Angular acceleration (typically around 4 to 7g) 
               
               
                 maintain −x o  ≤ x′ ≤ x o   
               
               
                 If x′ &gt; x o  then x′ = x o   
               
               
                 If x′ &lt; −x o  then x′ = −x o   
               
               
                   
               
            
           
         
       
     
     This system  100  (e.g., the air maintenance tire  10  described above) may be a force control system with a maximum pumping capability determined by the piston  16  moving a maximum distance to the right ( FIG. 2 ), as limited by one of the diaphragms  19 , X(i)=Xo and ΔPA&gt;m(rα−g cos θ). The maximum pumping pressure may be nΔP=n[m(rα−g cos θ)]/A psig. For example, a 50 g piston with a 5.0 mm diameter for 6 pumps at a constant speed, (α=0), ΔP may be 21.74 psig. A 50 g piston with a 5.0 mm diameter for 6 pumps at a 5.0 g acceleration, ΔP may be 130.43 psig. If the resistance, or cracking pressure Pcr, of the check valve  28  is not negligible, the maximum pumping pressure ΔP may be n(ΔP−Pcr). Thus, this system  100  may be driven by two forces components, gravitation G and acceleration A. The gravitation force G may provide a high frequency cyclic effect on the pumps  18  in a short distance. The acceleration force A may provide a low or medium frequency cyclic effect to ensure maximum pumping pressure. 
     Under a first example condition, a piston mass effect under constant speed, 6 pumps with 5.0 mm piston diameters, 4.0 mm length chambers (e.g.,  101 ,  102 ), and 3.0 mm maximum travel may be mounted on a 15″ wheel/tire ( FIGS. 10 &amp; 11 ). Under a second example condition, a number of piston effect under constant speed, 75.0 g pistons with 5.0 mm diameters, 4.0 mm length chambers (e.g.,  101 ,  102 ), and 3.0 mm maximum travel may be mounted on a 15″ wheel/tire ( FIGS. 12 &amp; 13 ). 
     In accordance with the present invention, the example air maintenance tire system  10  may use a free weight  201  sliding on a rail  202  to move the piston  16  to pump air ( FIG. 1 ). When the tire reaches the set pressure (e.g., 100 psi), however, the free weight may still move the piston  16  even though pressure is not needed. This unwanted piston movement may create unnecessary wear for the piston/pump  14 ,  16  and reduce the service life of the air maintenance tire system  10 . This unnecessary wear may be mitigated and/or eliminated by stopping the movement of the weight and piston the set pressure is achieved in the tire cavity. 
     In accordance with the present invention and as shown in  FIG. 1 , a stop mechanism  200  for the weight  201  may include a stop piston  210 , a stop cylinder  220 , a first spring  230 , and a second spring  240 . The first spring  230  may be disposed internally to the stop cylinder  220  with the first spring engaging both the top end of the stop cylinder and the stop piston  210 . The second spring  240  may be disposed internally to the stop cylinder  220  with the second spring engaging both the bottom end of the stop cylinder and the stop piston  210 . The stop cylinder  220  may have a first port  221  pneumatically connected to the tire cavity and a second port  222  pneumatically connected to ambient or another predetermined pressure. When air pressure in the tire cavity reaches the set pressure, the set pressure may overcome the force of the first spring  230  against the stop piston  210  and move the stop piston into a stopping engagement with the weight  201  ( FIG. 1 ). When air pressure in the tire cavity is below the set pressure, the second spring  240  may overcome the force of the first spring  230  inside the stop cylinder  220  and move the stop piston  210  away from the weight  201 . 
     While certain representative examples and details have been shown for the purpose of illustrating the present invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the present invention.