Abstract:
A tire condition monitoring apparatus includes transmitters. Each transmitter is installed in a vehicle tire and is powered by a battery. Each transmitter includes a sensor for detecting a condition of the associated tire, a transmission circuit for wirelessly transmitting data representing the condition and a controller that controls the sensor and the transmission circuit. The controller controls each sensor to detect the condition at predetermined detection intervals. Also, the controller controls the transmission circuit to transmit data that represents the detected condition only when the detected current tire condition has changed from the previously transmitted tire condition by a predetermined value α1 or more. As a result, significant changes of the tire condition are immediately communicated to a driver, and battery strength is conserved.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to an apparatus for monitoring the conditions of automobile tires. More particularly, the present invention pertains to a transmitter and method for transmitting data regarding the conditions of tires to a receiver mounted on a vehicle body.  
           [0002]    Wireless tire condition monitoring apparatuses for allowing a driver in a vehicle passenger compartment to check the conditions of vehicle tires have been proposed. One such monitoring system includes transmitters and a receiver. Each transmitter is located in one of the wheels and the receiver is located in the body frame of the vehicle. Each transmitter detects the conditions such as air pressure and the temperature of the associated tire and wirelessly transmits the detection information. The receiver receives the information from the transmitters.  
           [0003]    Since each transmitter is powered by a battery, the transmitter stops operating when the battery runs down. Each transmitter is attached to the corresponding wheel and is located in the corresponding tire. To change the battery of a transmitter, the tire must be removed from the wheel. Changing the battery of a transmitter is therefore burdensome. Further, the transmitters are constructed with high accuracy to endure the harsh conditions in the tire. Therefore, opening the casing of a transmitter for changing the battery can make the transmitter less reliable. Accordingly, changing the battery is not practical.  
           [0004]    The capacity of the battery may be increased to permit the transmitter to function for a long period without changing the battery. This, however, increases the size and the weight of the battery thus altering the balance of the corresponding tire. Therefore, the capacity of the battery cannot be increased beyond a certain limit.  
           [0005]    To extend the life of the batteries, some prior art apparatuses use transmitters that only periodically transmit signals. This minimizes the cumulative operating time of the transmitters, which allows batteries having a relatively small capacity to be used for a long period.  
           [0006]    Tire pressure can change at various rates. For example, natural leakage of air gradually decreases the pressure of a tire. When a tire goes flat due to damage, the air pressure drops quickly. Further, the rates of pressure loss from natural leakage and damage vary according to the circumstances. Thus, there is a demand for a monitoring apparatus that immediately detects air pressure changes regardless of the rate of pressure loss and extends battery life.  
           [0007]    However, simply making transmissions from a transmitter periodic cannot satisfy this need. As long as the tire pressure decreases slowly, relatively long transmission intervals cause no problem in detecting an abnormality. However, if the tire pressure suddenly decreases, the driver will not be immediately informed of the abnormality. If the transmission intervals are relatively short, the driver will be immediately notified of a sudden drop in tire pressure. However, the short intervals increase the cumulative operating time of the transmitter, which shortens the life of the battery.  
         SUMMARY OF THE INVENTION  
         [0008]    Accordingly, it is an objective of the present invention to provide a transmitter in a tire condition monitoring apparatus and a method that immediately inform a driver of tire condition changes and conserve battery strength.  
           [0009]    To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a battery-powered transmitter for wirelessly transmitting data regarding the condition of a vehicle tire is provided. The transmitter includes a sensor for detecting the condition of the tire, a transmission circuit for wirelessly transmitting data representing the detected tire condition and a controller for controlling the sensor and the transmission circuit. The controller controls the sensor to detect the tire condition at predetermined intervals. The controller controls the transmission circuit to transmit data that represents the detected current tire condition when a value representing the detected current tire condition has changed from a previously transmitted value representing the detected tire condition by a predetermined amount or by an amount that is greater than the predetermined amount.  
           [0010]    In another transmitter provided by the present invention, a controller controls a sensor to detect the tire condition at predetermined intervals. The controller controls a transmission circuit to transmit data that represents the detected current tire condition only when the detected current tire condition has changed from a tire condition that was detected in the past.  
           [0011]    The transmitter according to the present invention, together with a receiver for receiving data that is wirelessly transmitted from the transmitter, forms a vehicle tire condition monitoring apparatus.  
           [0012]    The present invention also provides a method for wirelessly transmitting data regarding the condition of a vehicle tire. The method includes detecting the condition of the tire at predetermined intervals and transmitting data that represents the detected current tire condition when the difference between a value representing the detected current tire condition and a previously transmitted value representing the detected tire condition is equal to or greater than a predetermined value.  
           [0013]    Another transmission method provided by the present invention includes detecting the condition of the tire at predetermined intervals and transmitting data that represents the detected current tire condition only when the detected current tire condition has changed from a tire condition that was detected in the past.  
           [0014]    Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:  
         [0016]    [0016]FIG. 1 is a diagrammatic view illustrating a tire air pressure monitoring apparatus according to a first embodiment of the present invention;  
         [0017]    [0017]FIG. 2 is a block diagram illustrating a transmitter in the apparatus of FIG. 1;  
         [0018]    [0018]FIG. 3 is a block diagram illustrating a receiver in the apparatus of FIG. 1;  
         [0019]    [0019]FIG. 4( a ) is a flowchart showing a pressure analysis procedure of the transmitter of FIG. 2;  
         [0020]    [0020]FIG. 4( b ) is a flowchart showing a temperature analysis procedure of the transmitter of FIG. 2;  
         [0021]    [0021]FIG. 5 is a timing chart showing operation of the transmitter of FIG. 2;  
         [0022]    [0022]FIG. 6 is graph showing the relationship between changes of tire pressure along time and operation of the transmitter shown in FIG. 2; and  
         [0023]    [0023]FIG. 7( a ) is a flowchart showing a pressure analysis procedure of a transmitter according to a second embodiment of the present invention; and  
         [0024]    [0024]FIG. 7( b ) is a flowchart showing a temperature analysis procedure of the transmitter of the second embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    A tire condition monitoring apparatus according to a first embodiment of the present invention will now be described with reference to FIGS.  1  to  6 . As shown in FIG. 1, the tire condition monitoring apparatus includes four tires  2  of a vehicle  1 , four transmitters  3 , each located in one of the tires  2 , and a receiver  4 , which is mounted on the body frame of the vehicle  1 . Each transmitter  3  is secured to the wheel of the associated tire  2  such that each transmitter  3  is located within the associated tire  2 . Each transmitter  3  detects the air pressure and the internal temperature of the associated tire  2  and sends data representing the detection information to the receiver  4 .  
         [0026]    As shown in FIG. 2, each transmitter  3  includes a controller  10 , which is, for example, a microcomputer. The controller  10  includes a central processing unit (CPU), a random access memory (RAM) and a read only memory (ROM). A unique ID code is registered in each controller  10 . The ID code is used to distinguish the associated transmitter  3  from the other three transmitters  3 .  
         [0027]    A pressure sensor  11  located in each tire  2  detects the internal air pressure of the associated tire  2  and sends data representing the detected pressure to the controller  10 . A temperature sensor  14  detects the temperature in the associated tire  2  and sends data representing the detected temperature to the controller  10 . The controller  10  sends the received pressure and temperature data and the ID code to a transmission circuit  12 . The transmission circuit  12  transmits data, which includes the pressure and temperature data and the ID code, to the receiver  4  through a transmission antenna  13 .  
         [0028]    A battery  15  powers the transmitter  3 . The controller  10 , the pressure sensor  11 , the transmission circuit  12 , the antenna  13 , the temperature sensor  14  and the battery  15  are housed in a casing (not shown).  
         [0029]    As shown in FIG. 5, the controller  10  commands the pressure sensor  11  and the temperature sensor  14  to perform detection at predetermined time intervals t 1 . The time interval t 1  will be referred to as a detection interval. A time period t 2  shown in FIG. 5 is a period from when the pressure sensor  11  and the temperature sensor  14  start detection until the resultant data is processed by the controller  10 . The time t 2  will be referred to as a detection time.  
         [0030]    When a predetermined transmission condition is satisfied based on the pressure data from the pressure sensor  11  and the temperature data from the temperature sensor  14 , the controller  10  commands the transmission circuit  12  to perform a transmission as shown by the broken line in FIG. 5. A time period t 3  in FIG. 5 represents a period during which the transmission circuit  12  is performing a transmission. The time t 3  will be referred to as a transmission time. The transmission condition will be discussed below with reference to the flowchart of FIGS.  4 ( a ) and  4 ( b ).  
         [0031]    The transmitter  3  is in a sleep state and consumes little battery energy other than during the measuring time t 2  and the transmission time t 3 . The detection interval t 1  is determined by considering the capacity of the battery  15 , the power consumption of the transmitter  3  and the operating times t 2 , t 3  of the transmitter  3 . In this embodiment, the detection interval t 1  is fifteen seconds.  
         [0032]    As shown in FIG. 3, the receiver  4  includes a controller  20 , which is, for example, a microcomputer. The controller  20  includes a central processing unit (CPU), a random access memory (RAM) and a read only memory (ROM). An RF circuit  21  receives data transmitted from the transmitters  3  through a reception antenna  22  and sends the data to the controller  20 . Based on the ID code and pressure and temperature data in the received data, the controller  20  obtains the internal pressure and temperature of the tire  2  corresponding to the transmitter  3  that has sent the data.  
         [0033]    The controller  20  also displays information regarding the tire pressure, the tire temperature and other data on a display  23 . The display  23  is located in the view of the driver. The controller  20  also controls an alarm device  24  to warn a driver of an abnormal tire pressure or an abnormal tire temperature. The alarm device  24  may be a device that generates sound or a device that emits light for indicating a tire abnormality. Alternatively, notice of a tire abnormality may be displayed on the display  23 . The receiver  4  is activated, for example, when the ignition key (not shown) is turned on.  
         [0034]    Operation of each transmitter  3  will now be described with reference of the flowchart of FIGS.  4 ( a ) and  4 ( b ). The controller  10  repeatedly performs the routine of FIGS.  4 ( a ) and  4 ( b ) every fifteen seconds, which is the detection interval t 1 .  
         [0035]    When the battery  15  is installed during the assembly of each transmitter  3 , the controller  10  commands the pressure sensor  11  and the temperature sensor  14  to perform the first detection. The controller  10  stores the first pressure detection value Pn and the first temperature detection value Tn as an initial pressure transmission value Pt and an initial temperature transmission value Tt and commands the transmission circuit  12  to transmit the initial transmission values Pt, Tt.  
         [0036]    The routine shown in FIG. 4( a ) relates to detection and transmission of the pressure in each tire  2 . In step S 1 , the controller  10  commands the pressure sensor  11  to detect the pressure in the tire  2 . In step S 2 , the controller judges whether the absolute value of the difference between a stored pressure transmission value Pt and a new pressure detection value Pn is equal to or greater than a predetermined pressure determination value α1. The stored pressure transmission value Pt was transmitted in the previous routine. The stored pressure transmission value Pt was stored in the memory of the controller  10  in a previous cycle of the routine. The new pressure detection value Pn is detected in step S 1 . That is, the new pressure detection value Pn is detected in the current cycle of the routine.  
         [0037]    The pressure determination value α1 is relatively small. Changes of the tire pressure within the range of the determination value α1 have little influence on the running conditions of the vehicle  1 .  
         [0038]    If the absolute value of the difference between the stored pressure transmission value Pt and the new pressure detection value Pn is less than the pressure determination value α1, the controller  10  judges that the air pressure of the tire  2  has changed in a small range and temporarily suspends the routine. If the absolute value of the difference between the stored pressure transmission value Pt and the new pressure detection value Pn is greater than the pressure determination value α1, the controller  10  judges that the air pressure of the tire  2  has changed relatively greatly and moves step S 3 .  
         [0039]    In step S 3 , the controller  10  stores the new pressure detection value Pn, which was detected in the current cycle of the routine, as the stored pressure transmission value Pt. In other words, the stored pressure value Pt is updated, or renewed, with the new pressure value Pn. In step S 4 , the controller  10  commands the transmission circuit  12  to transmit data that includes the stored pressure transmission value Pt. Then, the current routine is suspended.  
         [0040]    The routine of FIG. 4( b ) relates to detection and transmission of the temperature of each tire  2 . The routine of FIG. 4( b ) is executed concurrently with the routine of FIG. 4( a ). In step S 11 , the controller  10  commands the temperature sensor  14  to detect the temperature in the tire  2 . In step S 12 , the controller  10  judges whether the absolute value of the difference between a stored temperature transmission value Tt and a new temperature detection value Tn is equal to or greater than a predetermined temperature determination value α2. The stored temperature transmission value Tt was transmitted in the previous routine. The stored temperature transmission value Pt was stored in the memory of the controller  10  in a previous cycle of the routine. The new temperature detection value Tn is detected in step S 11 . That is, the new temperature detection value Tn is detected in the current cycle of the routine.  
         [0041]    The temperature determination value α2 is relatively small. Changes of the tire temperature within the range of the determination value α2 have little influence on the running conditions of the vehicle  1 .  
         [0042]    If the absolute value of the difference between the stored temperature transmission value Tt and the new temperature detection value Tn is less than the temperature determination value α2, the controller  10  judges that the temperature of the tire  2  has changed in a small range and temporarily suspends the routine. If the absolute value of the difference between the stored temperature transmission value Tt and the new temperature detection value Tn is greater than the temperature determination value α2, the controller  10  judges that the temperature of the tire  2  has changed relatively greatly and moves step S 13 .  
         [0043]    In step S 13 , the controller  10  stores the new temperature detection value Tn, which was detected in the current cycle of the routine, as the stored temperature transmission value Tt. In other words, the stored temperature value Tt is updated, or renewed, with the new temperature value Tn. In step S 14 , the controller  10  commands the transmission circuit  12  to transmit data that includes the stored temperature transmission value Tt. Then, the routine is suspended.  
         [0044]    [0044]FIG. 6 is a graph showing the relationship between changes of the pressure in each tire  2  and the operation of the associated transmitter  3 . During a period Ta in which the vehicle  1  is not moving, the air pressure of the tire  2  slightly fluctuates according to the outside temperature. Thus, the pressure detection value Pn, which is detected at the detection intervals t 1 , changes little. In other words, the new pressure detection value Pn is slightly different from the air pressure value that was transmitted in the previous routine, or the stored pressure transmission value Pt, however, the difference is less than the pressure determination value α1. Even if the data representing the air pressure is not transmitted during the period Ta, the current air pressure can be judged to be close to the air pressure that was transmitted in the previous routine.  
         [0045]    During a period Tb in which the vehicle  1  is moving, the temperature and the air pressure of the tire  2  increase due to the friction between the tire  2  and the road surface. Accordingly, the pressure detection value Pn, which is detected at every detection interval t 1 , gradually increases. When the new pressure detection value Pn exceeds the stored pressure transmission value Pt by the pressure determination value α1 or by a greater value, the new pressure detection value Pn is transmitted. That is, the new transmitted pressure detection value Pn is set as the stored new pressure transmission value Pt, and the stored pressure transmission value Pt is transmitted. While the vehicle  1  is moving in a normal state, that is, when the vehicle  1  is moving on a relatively smooth road surface without any abrupt changes of speed, the temperature and the air pressure of the tire  2  are substantially constant. Therefore, the new pressure detection value Pn changes little and the data representing the air pressure is not transmitted. In this case, the current air pressure can be judged to be in the vicinity of the air pressure that was previously transmitted.  
         [0046]    During a period Tc, at the beginning of which the vehicle is stopped, the temperature of the tire  2  decreases to approach the outside temperature. Accordingly, the air pressure of the tire  2  drops. If the difference between the new pressure detection value Pn and the stored pressure transmission value Pt is equal to or greater than the pressure determination value α1, the new pressure detection value Pn is transmitted. That is, the new pressure detection value Pn is set as the stored pressure transmission value Pt before the stored pressure transmission value Pt is transmitted.  
         [0047]    If the tire  2  goes flat during a period Td, in which the vehicle  1  is moving. The air pressure drops quickly. Accordingly, the difference between the pressure detection value Pn and the current pressure transmission value Pt exceeds the pressure determination value α1, and the pressure detection value Pn is immediately transmitted. Therefore, the driver of the vehicle  1  is immediately informed of an abnormality of the air pressure in the tire  2  through the display  23  of the receiver  4  or the alarm  24 .  
         [0048]    When the vehicle  1  is stopped (time Te) and the air pressure of the tire  2  is equal to the atmospheric pressure, the air pressure of the tire  2  stops declining. Thus, data regarding the air pressure is not transmitted. However, the current air pressure can be judged to be in the vicinity of the air pressure that was transmitted previously, or in the vicinity of the atmospheric pressure. Therefore, even if the data is not transmitted, an abnormality of the air pressure of the tire  2  is accurately detected.  
         [0049]    As described above, the transmitters  3  according to the embodiment of FIGS.  1  to  6  detect the condition of each tire  2  at predetermined time intervals and transmit the most recent data of the tire condition only when the value representing the current tire condition has changed from the value of the tire condition that was transmitted previously by a predetermined determination value or by a value greater than the determination value. In other words, if the tire condition is substantially unchanged, data is not transmitted. The data is transmitted only when the tire condition changes by a relatively great degree.  
         [0050]    The electricity needed for transmission is significantly greater than the electricity needed for detection. However, in the embodiment of FIGS.  1  to  6 , transmission is rarely performed when the vehicle  1  is not moving or when the vehicle  1  is moving in a normal state.  
         [0051]    When the driver needs to be immediately informed of the tire condition, for example, when the tire condition greatly changes, transmission takes place. Therefore, the driver is immediately informed of an abnormality in the tire condition. Also, if transmission does not take place for an extended period, the driver can accurately judge the current tire condition based on the tire condition that was received by the receiver  4  through the previous transmission.  
         [0052]    A second embodiment of the present invention will now be described with reference to flowcharts of FIGS.  7 ( a ) and  7 ( b ). The routines of FIGS.  7 ( a ) and  7 ( b ) are performed every fifteen seconds, which is the detection interval t 1 .  
         [0053]    When the battery  15  is installed during the assembly of each transmitter  3 , the controller  10  commands the pressure sensor  11  and the temperature sensor  14  to perform a first detection. The controller  10  stores a new pressure detection value Pn and a new temperature detection value Tn as initial values. The initial pressure detection values Pn and the initial temperature detection value Tn may be transmitted from the transmission circuit  12 . However, the initial detection values Pn, Tn need not be transmitted.  
         [0054]    The routine of FIG. 7( a ) relates to detection and transmission of the air pressure of each tire  2 . In step S 21 , the controller  10  commands the associated pressure sensor  11  to detect the air pressure in the tire  2 . In step S 22 , the controller  10  judges whether the absolute value of the difference between the new pressure detection value Pn, which was detected in the current cycle of the routine, and a previous pressure detection value Pn−1, which was detected in the previous routine, is zero. The previous pressure detection value Pn−1 is stored in the memory of the controller  10 .  
         [0055]    When the absolute value of the difference between the new pressure detection value Pn and the previous pressure detection value Pn−1 is zero, the controller  10  judges that the air pressure in the tire  2  has not changed and moves to step S 24 . If the absolute value of the difference is not zero, the controller  10  judges that the air pressure in the tire  2  has changed and moves to step S 23 .  
         [0056]    When the judgment of whether the absolute value of the difference is zero is made, errors in acceptable ranges such as errors due to the characteristics of the pressure sensor  11  are not considered.  
         [0057]    In step S 23 , the controller  10  commands the transmission circuit  12  to transmit data including the new pressure detection value Pn. In step S 24 , the controller  10  stores the new pressure detection value Pn as the previous pressure detection value Pn−1 and temporarily suspends the routine.  
         [0058]    The routine of FIG. 7( b ) relates to detection and transmission of the temperature of each tire  2 . The routine of FIG. 7( b ) is executed concurrently with the routine of FIG. 7( a ). In step S 31 , the controller  10  commands the temperature sensor  14  to detect the temperature in the tire  2 . In step S 32 , the controller  10  judges whether the absolute value of the difference between the new temperature detection value Tn and a previous temperature detection value Tn−1, which was detected in the previous routine, is zero. The previous temperature detection value Tn−1 is stored in the memory of the controller  10 .  
         [0059]    If the absolute value of the difference between the new temperature detection value Tn and the previous temperature detection value Tn−1 is zero, the controller  10  judges that the temperature in the tire  2  has not changed and moves to step S 34 . If the absolute value of the difference is not zero, the controller  10  judges that the temperature of the tire  2  has changed and moves step S 33 .  
         [0060]    When the judgment of whether the absolute value of the difference is zero is made, errors in acceptable range such as errors due to the characteristics of the temperature sensors  14  are not considered.  
         [0061]    In step S 33 , the controller  10  commands the transmission circuit  12  to transmit data including the new temperature detection value Tn. In step S 34 , the controller  10  stores the new temperature detection value Tn as the previous temperature detection value Tn−1 in its memory and temporarily suspends the routine.  
         [0062]    The embodiment of FIGS.  7 ( a ) and  7 ( b ) has the same advantages as the embodiment of FIGS.  1  to  6 .  
         [0063]    It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the invention may be embodied in the following forms.  
         [0064]    The detection interval t 1  is not limited to fifteen seconds but may be altered according to the type of the tires  2 , in which the transmitters  3  are mounted.  
         [0065]    In the embodiment of FIGS.  1  to  6 , the pressure determination value α1 and the temperature determination value α2 may be altered according to the type of the tires  2 , in which the transmitters  3  are mounted.  
         [0066]    In the embodiment of FIGS.  7 ( a ) and  7 ( b ), the detected current tire condition is transmitted only when the detected current tire condition has changed from a previously detected tire condition. However, the data representing the current tire condition may be transmitted when the current tire condition is different from the data that was detected in a cycle of the routine that occurred earlier than the previous cycle.  
         [0067]    The present invention is effective as long as the air pressure in each tire  2  is detected and transmitted. That is, detection and transmission of the tire temperature may be omitted. This permits a transmitter  3  that has minimized but necessary functions to be inexpensively manufactured.  
         [0068]    Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.