Abstract:
A wireless dual tire pressure monitor and equalizer apparatus is adapted to install on a vehicle dual wheel and connect to the two tire valve stems. The apparatus includes capabilities of monitoring individual tire pressure and transmitting tire data to be received by a remote receiver, equalizing pressure in the two tires when pressure is above a selected level, isolating the two tires when pressure is below the selected level, and transmitting warning signals upon detection of low pressure and air leaks. The apparatus further includes capability to integrate with available tire inflation systems for providing tire pressure monitoring and equalizing functionalities.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to the field of dual tire pressure monitoring with pressure equalizing feature. Particularly, the invention relates to a miniature external wheel mounted apparatus with built-in tire pressure monitoring circuitry and dual tire equalizer having one valve stem for air intake plus two air outlet valve stems for connecting to the dual tires, that the apparatus allows refilling tire air through one valve stem to the two tires, and the built-in pressure sensors can monitor individual tire of the dual tire pressure in real time and transmit the tire information to a remote device by wireless means, that the built-in dual tire equalizer can balance the dual tire pressure in normal operating condition, and can isolate the two tires when pressure dropped below a certain level, and methods for constructing and operating the apparatus. The invention further relates to integrating the dual tire pressure monitor with equalizer to tire inflation systems. 
       BACKGROUND OF THE INVENTION 
       [0002]    In commercial and off-the-road vehicles, wheel assemblies having dual pneumatic tires are commonly used, with typically a set of dual tires mounted on each end of an axle. During normal operation of such a vehicle the air pressure in the dual tires may not be equal. This can be caused by improper inflation, uneven heating of the tires, or an air leak in either tire. Correct and properly balanced pressure in the dual tires will help to provide even wear and longer life of the expensive tires. Numerous innovations for equalizing dual tire pressure have been provided in prior arts but few covered dual tire pressure monitoring. Some innovations are related to dual tires equalizer with a simple mechanical pressure indicator. For direct pressure monitoring, electronic pressure sensors have long been used to monitor tires for determining whether the tire was properly pressurized. However most related prior inventions for tire pressure sensors were for single tire pressure monitoring only. Numerous innovations for inflating dual tires also have been provided but few covered controlling tire inflation with real-time dual tire pressure measurements. 
         [0003]    U.S. Pat. No. 4,539,928 issued to Gordon R. Todhunter on Sep. 10, 1985 discloses a tire equalizer device that comprises a housing having upper and lower chambers divided by a flexible diaphragm opposing a seat in the upper chamber connected to one of the tires. The diaphragm is urged toward the seat by a spring-pressed inverted cup larger in diameter than the diaphragm and having an arm extended longitudinally from the cup away from the spring. The arm is curved in horizontal cross-section and its upper end is formed with a slot receiving an off-center pin on the back of an indicator disc. Also connected to the upper chamber is a fill conduit, and a conduit to the other tire. 
         [0004]    U.S. Pat. No. 5,302,939 issued to Edward A. Downs on Apr. 12, 1994 discloses a dual tire equalizer having a diaphragm that pushes a spring-loaded rod between two switch devices which, when the tire is not properly pressurized, will trigger the sending of an encoded RF signal to a receiver for generating alarms. 
         [0005]    U.S. Pat. No. 5,302,939 issued to Edward A. Downs on Apr. 12, 1994 discloses a method and apparatus for maintaining equal air pressure in a dual tire. The invention provides a valve body with a pair of piston chambers. 
         [0006]    U.S. Pat. No. 7,656,281 issued to Joe Huayue Zhou on Feb. 2, 2010 discloses an external valve stem mounted tire pressure monitoring sensor with air flow through feature. Particularly, the invention relates to an apparatus of a miniature external valve stem mounted tire pressure sensor design that allows refilling tire air through the sensor built-in valve stem without needing to remove the sensor, and methods for constructing and operating the apparatus. 
         [0007]    Typically, these systems teach equalizing dual tires without continuous pressure monitoring and remote notification, or only do tire pressure monitoring without dual tire equalizing. Furthermore, these teachings do not address or not able to resolve many practical issues, as described below: 
         [0008]    (i) Dual Tire Pressure Monitor with Equalizer Function 
         [0009]    Properly pressurized and equalized tires in a dual tire set are utmost important for safe driving and for prolonging the life of tires. However prior tire pressure monitoring systems (TPMS) generally only monitor tires without pressure equalization and, therefore, can only be used as a separate system to support tire monitoring for the dual tire pressure equalizing systems. It is technically challenging to make a small, integrated dual tire pressure monitor with equalizer that can monitor individual tire pressure in a dual tire set, refill air without removing the sensor, and equalize the pressure in the two tires. Prior teachings generally do not present practical methods to make small external dual tire sensors with pressure equalizer. 
         [0010]    (ii) Dual Tire Pressure Monitor with Equalizer and Tire Inflation System Integration 
         [0011]    There are many tire inflating systems available on the market and most of them are designed for trailer installation. Such systems use compressed air from the trailer air tank to inflate tires having pressure that fell below a preset level. Air from the existing trailer air supply is routed to a control box and then fed into air tubes installed inside each axle. The air tubes run through the axles to carry air through a rotary union assembly joined at the wheel spindle end in order to distribute air to each tire. 
         [0012]    Although good tires usually able to keep proper pressure for weeks, a tire inflation system on a vehicle often must operate every trip due to possible air line and seal leaks. In addition, tire inflation systems generally do not have direct pressure readings from the dual tires for controlling the inflation and, therefore, must inflate from time to time and check if the preset pressure was maintained on the air line. If pressure was still low after a period of time then the systems would deduce that there might be a leaky or flat tire. This indirect detection of air leak and flat tire is unreliable and usually belated, and the excessive work load putting on the rotary hub seal unit and the air compressor will wear out the parts sooner and would lead to more expensive vehicle maintenance and even unsafe driving conditions. A tire inflation system integrated with tire pressure monitor and equalizer would have accurate inflation control based on real-time tire pressure data and, as a result, works less and thereby reduces the vehicle maintenance costs; most importantly such an integrated system improves vehicle safety for it would be able to notify the driver low or flat tire condition immediately. 
         [0013]    A tire inflation system integrated with a direct tire pressure monitor, even without the pressure equalizing function, can also provide substantial benefits in accurate inflation control, improved vehicle safety, and system maintenance cost reductions. 
       SUMMARY OF THE INVENTION 
       [0014]    A main object of the present invention is to provide a miniature dual tire pressure monitoring sensor with dual tire equalizer feature, which can be easily mounted on the vehicle dual wheel and connected to the tires. 
         [0015]    Another object of the invention is to provide a dual tire pressure monitoring system with miniature dual tire sensors that can be easily mounted on the outside dual wheel and connected to the tires, for applications not needing tire pressure equalization. 
         [0016]    Another object of the invention is a method for the dual tire pressure monitor with equalizer to integrate with trailer dual tire inflation systems. 
         [0017]    Another object of the invention is a method for manually triggering pressure sensor signal transmission by applying a magnetic field near the tire sensor. It provides a simple and reliable sensor signal triggering method for tire monitoring system programming and services. 
         [0018]    Another object of the invention is a method for manually triggering pressure sensor signal transmission by applying a Low Frequency (LF) wireless signal near the tire sensor. It provides a simple and reliable sensor signal triggering method for tire monitoring system programming and services. 
         [0019]    Another object of the invention is a method for pressure sensor battery replacement. 
         [0020]    Another object of the invention is a method for a tire pressure monitor to integrate with trailer tire inflation systems. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is an assembly drawing of the dual tire pressure sensor with equalizer module. 
           [0022]      FIG. 2  is a drawing of the dual tire pressure sensor with equalizer half-section view. 
           [0023]      FIG. 3  is a drawing of the pressure equalizer sectional view. 
           [0024]      FIG. 4  is a drawing of the dual pressure sensor mounting oblique view. 
           [0025]      FIG. 5  is an assembly drawing showing the dual tire pressure sensor PCB and a replaceable battery. 
           [0026]      FIG. 6  is a drawing of dual tire pressure sensor and equalizer with wheel mounting bracket. 
           [0027]      FIG. 7  shows the dual tire pressure sensor with equalizer installation on dual wheel. 
           [0028]      FIG. 8  shows a dual tire pressure sensor with equalizer installation on dual wheel and integrated with an existing tire inflation system. 
           [0029]      FIG. 9  is a schematic of the dual tire pressure sensor electronic circuitry. 
           [0030]      FIG. 10  is a system design of the dual tire pressure sensors with equalizer integrated with a trailer tire inflation system. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0031]    An embodiment of the invention is described herein with references to the figures using reference designations as shown in the figures. 
         [0032]      FIG. 1  shows the assembly of the dual tire pressure sensor with equalizer module, where  101  is a lock ring with threads screwing onto a rigid module body  106  to secure a spring holder cap  102  that contains a spring  103 , an inverted cylindrical cup  104  and a diaphragm  105 . On the other side of the module body where  107  is the dual sensor electronic PCB,  108  is the replaceable battery PCB with battery holder,  109  is a waterproof sealing o-ring and  110  is the battery cap with threads. 
         [0033]      FIG. 2  shows a half-section drawing of the dual tire sensor with equalizer module. Referring to  FIG. 2 , the assembly comprises a rigid module body  204  with the upper portion having a spring holder cap  201  holding a spring  203  that extended downward to bear on an inverted cylindrical cup  206  and a diaphragm  207  beneath; the space formed above diaphragm  207  and enclosed by cap  201  defines an upper chamber  205 . Enclosed by the module body shell, the recess beneath diaphragm  207  defines a lower chamber  209  with a seat  208 ; the lower chamber  209  has a passage communicating to the air inlet valve stem  202 . Centrally diaphragm  207  is able to engage the seat  208  underneath, which at its center has an opening with air passage  211  leading to a pressure sensor air hole  212  and an air outlet  213 ; another pressure sensor hole and air outlet are showed in  FIG. 3 . A threaded hole  210  on the module body supports fastening the module on a bracket for mounting on a dual wheel. On the bottom portion of the module are the pressure sensor battery  214  and the battery cap  215 . 
         [0034]      FIG. 3  shows a sectional view of the dual sensor with equalizer module. In the drawing diaphragm  305  separates lower chamber  304  from upper chamber  302  that contains spring  301  and inverted cylindrical cup  303 . Lower chamber  304  has passages communicate respectively with an air inlet (showed in  FIG. 2 ), an air outlet  309  for one tire, and a pressure sensor  310 . When diaphragm  305  is not engaged with seat  306 , the lower chamber  304  also communicates through passage  307  with opening at the center of seat  306  to air outlet  308  for the other tire, and to another pressure sensor  311 . 
         [0035]    By virtue of the dual sensor with equalizer module structure described thus far, sufficient air pressure in the lower chamber will urge the diaphragm  305  and cup  303  assembly upward and away from seat  306  against the downward force of spring  301 , permitting the two tires to communicate; this equalizes the pressure in the dual tires. A drop in pressure will allow spring  301  to drive the cup  303  and diaphragm  305  downward to engage the seat  306  and close off communication between the two tires. 
         [0036]      FIG. 4  shows an oblique view drawing of the dual tire pressure sensor assembly, where two port type piezo-resistive pressure sensors  401  and  402  are mounted on the underside of a print circuit board for mating respectively to air holes  405  and  406  that communicate to respective air outlets  308  and  309 ; o-rings  403  and  404  support the sensor to air hole mating for forming an airtight sealing. 
         [0037]      FIG. 5  shows an assembly drawing of the dual tire pressure Sensor PCB and replaceable battery. PCB  504  with pressure sensors  503  is installed onto air holes  501  with o-rings  502  the same way as earlier  FIG. 4  descriptions, and secured by set screws onto the module body. PCB  505  is stacked on PCB  504  to provide power supply with a replaceable battery  506 , which is mounted on the backside of PCB  505  and encapsulated by a threaded cap  508  with a waterproof sealing o-ring  507 . To protect the delicate and sensitive electronics after mounting, epoxy compounds can be used to fill up the spaces underneath PCB  504  and  505 . Through the air holes the two sensors are directly exposed to air pressure of the respective tire. When the two tires are communicating, that is, when diaphragm  305  is not engaged with seat  306 , both sensors will be measuring the pressure from the same source. However when lowering pressure caused diaphragm  305  to engage with seat  306  and close off tire communication, then each sensor will be reading the pressure of its own tire. 
         [0038]      FIG. 6  shows the dual tire pressure sensor and equalizer module  603  fasten on a bracket  601 , where mounting bolt  602  with a lock washer is inserted through a hole in bracket  601  and screwed into the threaded hole  210  in the module body. A large hole  604  in bracket  601  allows mounting the dual tire pressure sensor and equalizer module on a dual wheel. When fastening to bracket  601 , battery cap  605  of module  603  is oriented toward hole  604 , so that after mounting on the wheel the module electronics portion would be facing the wheel and therefore would have a less chance of being damaged by possible flying debris on the road. 
         [0039]      FIG. 7  shows the dual tire pressure sensor with equalizer module installation on a dual wheel, where a bracket and module assembly is mounted on one of the wheel bolts or studs with two hoses each connecting one of the two module air outlets to respective inner and outer tire valve stems. Tire air can easily be filled through the module air inlet valve stem and the dual tire pressure can be equalized by mechanism inside the module. With a remote cab-mounted RF receiver, the driver can monitor dual tire pressure in real-time. 
         [0040]      FIG. 8  shows a wheel mounted dual tire pressure sensor and equalizer module  801  being integrated with an existing tire inflate system, where an air outlet  804  on the flow-through tee of the inflation system is connected by a short hose  803  with an adapter to the dual tire pressure sensor and equalizer module air inlet; the other air outlet  805  of the flow-through tee will be sealed off by a block cap. Hose  802  connects one of the module  801  air outlets to one of the dual tires, and hose  806  connects the other module air out to the second tire. The integrated systems now will have the functionalities of inflating tires, equalizing dual tire pressure, and monitoring tires in real-time. 
         [0041]    In operation, the dual tire pressure sensor with equalizer module is installed on a dual wheel as showed in  FIG. 7  or  FIG. 8 , with the two hoses  802  and  806  connecting the two air outlets respectively to the dual tire valve stems. The two tires are then filled through the module air inlet  202 . When tires are empty or have low pressure, spring  203  in the module forces cup  206  and diaphragm  207  to move downward and engage seat  208 , thereby closes off communication between the two tires. When sufficient air is filled through module air inlet  202  into lower chamber  209  and through an air outlet to one tire, the built up pressure overpowers the force of spring  203  exerted on cup  206  and diaphragm  207  and disengages diaphragm  207  from seat  208 , thereby opens up communication between the two tires and permits air flowing into the other tire. When the tires are sufficiently pressurized and not leaking, communication between the two tires will remain open and tire equalization is achieved. When pressure drops to a certain level due to air loss from one or both tires, communication between two tires will be closed off as described earlier. In this case, with a regular tire equalizing system it is possible that a leaky tire might continue losing air to a dangerously low level but the driver would have no knowledge of the imminent safety hazard. With the dual tire pressure sensor and equalizer described herein, however, pressure sensors  310  and  311  in the apparatus will continuously measure the pressure level of the two tires and send the data and any warnings by wireless transmission to a monitor mounted in the driver cab. The driver now can learn of the tire pressure conditions at anytime, receive alerts of tire pressure problems as it happened, and able to take corrective actions accordingly. Current tire inflation systems merely turn on an indicator light to notify the driver when the tires are being inflated, and it is up to driver to deduce the severity of air loss based on how long and how often the inflation has been happening. In contrast, a tire inflation systems integrated with the apparatus described will continuously display the current tire pressure data on the monitor, so that the driver can easily and quickly identify tire pressure related problems indicated by irregular and fluctuating individual tire pressure readings. 
         [0042]      FIG. 9  shows a schematic diagram for the electronic design of the dual tire pressure sensor module sensory logic and RF signal transmitter functions. Sensory electronics include two piezo-resistive pressure sensors U 4  and U 6 , which comprises four strain resistant sensitive resistors diffused in silicon. These resistors are connected in a Whetstone bridge configuration, whereby two resistors increase resistance with positive pressure while the other two resistors decrease in resistance. When pressure is applied to sensors, the resistors in the arms of the bridge of sensors changed resistance by an amount directly proportional to the pressure applied. When a voltage is applied to the bridge, there will be a resulting differential output voltage indicating sensed tire pressure. 
         [0043]    Sensory logic further consists two micro-power amplifiers U 3  and U 5  connected to respective sensor bridge U 4  and U 6  and supported by resistors R 2  through R 9 , plus a high performance CMOS eight-bit microprocessor U 2  with filter capacitors C 4  and C 5  processes data, controls I/O and manages power. The micro-power amplifiers U 3  and U 5  condition the sensed tire pressure voltage signal for input to the on-chip A/D converter of microprocessor U 2 , thereby producing digital readings of the tire pressure sensed by sensor U 4  and U 6 . To reduce component cost, this design utilizes one microprocessor to process inputs from both pressure sensors and then combines the dual tire pressure data to form a single message for RF signal transmission. The radio frequency transmitter consists of a transmitter IC U 1 , inductor L 1 , capacitors C 1 , C 2 , C 3 , C 6 , C 7 , and a crystal Y 1  for providing a transmitter frequency signal at 433.92 MHz or 313 MHz. The transmitter is modulated by microprocessor U 2  at pin  3  and enabled at pin  2 . 
         [0044]    For reducing the circuit size, an internal 4 MHz RC oscillator is used to clock microprocessor U 2 . Under program control, microprocessor U 2  outputs an encoded digital message data string for amplitude shift key modulating the carrier signal from the RF transmitter circuit. To minimize power consumption, the tire pressure sensor module operates in a dormant mode and only wakes up every few seconds and then spends several milliseconds checking the pressure sensors. If there has been a significant pressure change, such as +/−2 PSI, from the previous reading, the sensor module immediately transmits an ASK modulated radio frequency signal with encoded message to the monitor. From time to time the module also sends a “heartbeat” message with the current pressure readings to the monitor. The RF message consists of the sensor module ID, tire air pressure value, temperature value, battery level data, and checksum. To reduce RF signal transmission time for saving power usage, a compact data packing format is developed for sending dual tire pressure data in a message having only 8 data bytes. Usually tire pressure sensor message uses 4 bytes for sensor ID, but the compact format only uses 3 bytes for sensor ID while using one byte for status indication. Half of the status byte, i.e., 4 bits, is used for single or dual tire indication, while the other half byte is for storing sensor status such as low battery, vehicle in motion or stationary, rapid pressure change, and Low Frequency (LF) signal trigger. The remaining data consists of the outer tire pressure byte, inner tire pressure byte, dual tire temperature byte, and the checksum byte. In this arrangement, an 8 byte data format can contain enough information for the dual tire pressure sensor. 
         [0045]    Referring to  FIG. 10 , it is a system design of the dual wheel sensor with equalizer integrated with any tire inflation systems having pipes and hoses supplying air to the tires through the valve stem. The TPMS for integrating with a tire inflation system consists of a dual tire sensor with equalizer for each dual tire set as showed in earlier figures, a TPMS controller box, and an apparatus with an air solenoid valve controllable by the TPMS controller. The TPMS controller box consists of RF receiver  1001 , CPU controller  1002 , power management  1003  and I/O controller  1004 . CPU  1002  processes real time tire pressure data from RF receiver  1001 , and the I/O controller  1004  turns on or off the low pressure alarm lamp for notifying the driver. I/O controller  1004  also controls the opening and shutting off of the air solenoid valve  1005 . 
         [0046]    The dual tire sensor with equalizer is integrated to the tire inflation system air supply outlet to the tires, as showed in  1006  and  FIG. 8 . The solenoid valve air inlet is now connected to the trailer air tank outlet, and the tire inflation system controller air inlet is re-routed and connected to the solenoid valve air outlet. The weatherproof TPMS controller box can be installed on the trailer chassis, powered by the trailer power supply, and wired to the solenoid valve apparatus. The TPMS controller box receives real time tire pressure data transmitted from the dual tire sensor with equalizer and, based on a preset and configurable desired pressure level, commands the solenoid valve to open for air to pass through when the tire pressure is low or shut off the valve when pressure is normal; the tire inflation system will not operate if the TPMS controller cut off its air supply. The solenoid valve can also be installed inline after the inflation system controller air outlet; the tire inflation system will not operate if the TPMS controller blocked off the air outflow. The solenoid valve is normally open so that tire inflation would not be blocked in case the TPMS controller is not operating. 
         [0047]    A tire inflation system integrated with the above presented apparatus having real time tire pressure measurement and inflation control functionalities would be a greatly improved inflation system for tire safety and maintenance, offering continuous tire condition awareness, accurate tire inflation control, pressure equalization, fast response to rapid tire pressure changes, and much reduced