Method and apparatus for determining tire condition and location

An apparatus (10) determines a tire condition and location on a vehicle (12) including a tire-based sensing unit (14) including, a first tire rotation sensor (66) for providing a first tire rotation signal (80) each time the tire passes one of at least two predetermined rotational positions and an unique tire identification indicator, a transmitter (86) and a controller for controlling the transmitter so that the transmission occurs when the first tire rotation signal indicates the tire has reached one of the at least two predetermined rotational positions. The apparatus further includes a second tire rotation sensor (22) mounted external of the tire for sensing tire rotation and for providing a second tire rotation signal indicative of incremental angular position of the tire relative to a reference. A vehicle-based receiver (44) correlates reception with a particular tire location on the vehicle.

TECHNICAL FIELD

The present invention relates to a method and apparatus for determining a tire condition and location on a vehicle in a tire pressure monitoring system.

BACKGROUND

Systems for sensing tire conditions and displaying sensed tire condition information to a vehicle occupant are known. Often, such systems are known as tire pressure monitoring (“TPM”) systems even though the system may sense tire conditions in addition to pressure, such as tire temperature. Such TPM systems include a tire-based sensor assembly that senses, for example, the air pressure and temperature inside its associated tire and transmits the sensed tire condition information to a vehicle-based receiver, i.e., a receiver mounted in the vehicle. The transmitted sensed tire condition signal may be a coded radio frequency (“RF”) signal. The vehicle-based receiver is connected to a display located in the vehicle cabin so as to display, for example, a warning signal to the vehicle operator when an under-inflated tire pressure condition exists or an over-heated tire condition occurs.

Each tire-based sensor assembly may have a unique identification (“ID”) code associate therewith. The tire-based sensor assembly may transmit a signal that includes its associated unique ID code along with the sensed tire condition. The vehicle-based receiver can associate the received tire signal and unique ID with a particular tire location on the vehicle such as front right (“FR”), front left (“FL”), rear right (“RR”), or rear left (“RL”). By associating the tire ID with the tire location on the vehicle, the vehicle-based receiver is able to display the sensed tire condition information at each particular tire location so the vehicle operator can identify which tire (i.e., tire location) has a sensed, improper condition.

Associating a tire location with a tire-based transmitted ID code for each of the tire locations requires a “learning” process by the vehicle-based receiver. Methods have been proposed to accomplish this learning function including using signal interrogation in which each tire-based sensor assembly includes a receiver that is separately interrogated from a transmitter located outside of the tire using, for example, a low frequency (“LF”) interrogation signal. In response to receiving an interrogation signal, the tire-based sensor assembly transmits a response signal having its unique ID. Upon receipt of the response signal, the vehicle-based receiver associates that unique tire ID with that tire location since the system “knows” which tire location was just interrogated. The vehicle-based system stores tire-based sensor IDs and tire location associations in memory for later use in its display operation.

Some TPM systems have been proposed in which the tire-based system includes a tire rotation sensor. The tire-based system transmits a tire ID, tire rotation values, and tire condition information. Each tire has an associated external wheel rotation sensor that monitors wheel rotation and determines second rotation values for each wheel. A controller associates tire location by comparing, with sufficient coincidence, the tire-based rotation values with the externally monitored rotation values to establish tire location allocation. These arrangements, however, require that each transmitted tire-based signal include tire rotation values along with the tire condition values. The transmission of the tire rotation values each transmission of tire condition information results in wasted energy of the tire-based sensor which may be powered by a battery since the transmitted RF signal has to have at least two information portions, i.e., tire rotation information and tire condition information, for location allocation.

SUMMARY OF THE INVENTION

The present invention is directed to a method and apparatus for determining a tire condition and location on a vehicle.

In accordance with an example embodiment of the present invention, an apparatus determines a tire condition and location on a vehicle including a tire-based sensing unit, a plurality of tires on the vehicle having an associated tire-based sensing unit, each tire-based sensing unit including a first tire rotation sensor mounted for rotation with the tire and for providing a first tire rotation signal each time the tire passes one of at least two predetermined rotational positions during tire rotation, a tire condition sensor for sensing a tire condition and for providing a tire condition signal indicative thereof, and an unique tire identification indicator, a transmitter for transmitting the tire condition signal and the unique tire identification indicator, a controller for controlling the transmitter so that the transmission of the tire condition signal and the unique tire identification indicator occurs when the first tire rotation signal indicates the tire has reached one of the at least two predetermined rotational positions during tire rotation. The apparatus further includes a second tire rotation sensor mounted external of the tire for sensing tire rotation and for providing a second tire rotation signal indicative of incremental angular positions of the tire relative to a reference. A vehicle-based receiver receives the transmitted tire condition signal, the unique tire identification indicator, and the second tire rotation signal and correlates reception of the tire condition signal with the second tire rotation signal so as to associate the unique tire identification indicator with a particular tire location on the vehicle.

In accordance with another example embodiment of the present invention, a method for determining a tire condition and location on a vehicle comprises the steps of sensing tire rotation and providing a first tire rotation signal each time the tire passes one of at least two predetermined rotational positions during tire rotation, sensing a tire condition and for providing a tire condition signal indicative thereof, transmitting the tire condition signal and a unique tire identification indicator when said first tire rotation signal indicates the tire has reached one of said at least two predetermined rotational positions during the tire rotation, sensing tire rotation relative to the vehicle and providing a second tire rotation signal indicative of incremental angular positions of the tire relative to a reference, receiving said transmitted tire condition signal, the unique tire identification indicator, and said second tire rotation signal, and correlating reception of said tire condition signal with said second tire rotation signal so as to associate the unique tire identification indicator with a particular tire location on the vehicle.

DETAILED DESCRIPTION

Referring toFIG. 1, a tire pressure monitoring (“TPM”) system10, made in accordance with an example embodiment of the present invention, is shown mounted on a vehicle12. The TPM system10includes a plurality of sensors14(“S1”),16(“S2”),18(“S3”), and20(“S4”) located at each of the four corners front right (“FR”), front left (“FL”), rear right (“RR”), and rear left (“RL”), respectively, of the vehicle12. It should be understood that the sensors14,16,18, and20are mounted in their associated tires in any of several known arrangements. For example, each of the TPM sensors can be mounted as part of the valve stem assembly, can be mounted in a separate housing and attached to the wheel rim, or to the side of the tire itself. Each of the sensors14,16,18, and20include a sensor for sensing at least two predetermined angular positions of the tire during tire rotation and a sensor for sensing at least one condition of the tire, such as pressure and/or temperature. The sensors14,16,18, and20further include a transmitter, such as a radio frequency (“RF”) transmitter, for transmitting the sensed tire condition information.

The TPM system10further includes wheel rotation sensor assemblies22,24,26, and28located at associate FR, FL, RR, and RL corners of the vehicle, respectively, and mounted external of the associated tire at that vehicle corner location. Each external wheel rotation sensor assembly22includes a circular toothed plate or disc30that is mounted so as to rotate with its associated tire. A sensor32senses passing of each tooth of the disc30passed the sensor as the tire rotates and provides an electrical signal indicative thereof. The wheel rotation sensor assemblies22,24,26,28may be part of the vehicle's anti-lock braking system (“ABS”) and may be referred to as wheel speed (“WS”) sensors. Each sensor32of the wheel rotation sensor assemblies is connected to an ABS electronic control unit (“ECU”)40.

The TPM system10further includes a vehicle-based receiver/controller44. The receiver/controller44is connected to the ABS ECU and receives wheel rotation signals indicative of the incremental angular position of each of the wheels at the four corners of the vehicle via the sensor32and the toothed disc30. The receiver/controller44also includes a receiving antenna46for receiving RF signals indicative of tire condition information from each of the tire sensors14,16,18, and20. The receiver/controller44is connected to a display48for displaying tire condition information for each of the tires at each of the vehicle corners. The display48can take any of several known forms including a liquid crystal display (“LCD”).

Referring toFIG. 2, a tire54located at the FR corner of the vehicle includes the TPM sensor14operatively mounted to the tire54for sensing tire rotation and tire condition. The wheel rotation sensor22has its toothed disc30mounted so as to rotate with the tire54. The sensor32provides an electrical signal indicative of each tooth of disc30passing by the sensor32. In accordance with one example embodiment of the present invention, the toothed disc has seventy two teeth56equally spaced about the disc30with one tooth missing (total of seventy one teeth). Each time a tooth passes the sensor32a pulse is provided. Any of several types of sensors could be used for sensor32including an inductive sensor, a Hall Effect sensor, etc. If there are seventy two teeth locations, a pulse is output from the sensor32every five degrees except when the missing tooth location58is encountered. The missing tooth location58is designated as the zero wheel position and can function as a reference point.

The output from the sensor32is connected to the ABS controller40. The ABS controller monitors the output of the sensor and determines the angular position of the disc30, and, in turn, the angular position of the wheel54, relative to the zero wheel disc position, i.e., when the space58passes the sensor32. It should be appreciated that, although no signal is generated as the space58on the disc30passes the sensor32, the ABS ECU receives a continuous stream of pulses when the tire54is continuously rotating during normal vehicle movement and when there is a missing pulse, the ABS ECU “knows” that half way between the last pulse and the next received pulse is the “zero position.” The ABS ECU then knows that each pulse received after the zero position is equal to five degrees of rotation. The angle monitoring/determination continuous as the disc30and wheel54rotate with the zero position restarting the angle determination each complete revolution. The ABS ECU is connected to the vehicle-based TPM receiver/controller44.

The tire-based sensor14includes a TPM circuit64that includes the tire condition sensor and a tire rotation sensor that senses at least two predetermined angular positions of the tire54as it rotates. As shown inFIG. 3, an example embodiment of the present invention is shown in which the tire-based sensor14can transmit its tire condition RF signal at two separated angular positions of the tire54as the tire rotates during normal vehicle movement, e.g., not parked but moving. By providing for transmission at two spaced-apart angles, an RF-null position occurrence is avoided.

Referring toFIG. 4, the tire-based sensor14includes a circuit60. Those skilled in the art will appreciate that the control functions of the circuit60could be accomplished using a controller, such as a microcontroller, by using discrete circuitry, a combination of different types of circuitry, or an application specific integrated circuit (“ASIC”) and can be embodied in either the analog or digital domain. Each of the tire-based sensors14,16,18,20is constructed and operates in a similar manner.

An accelerometer66may be a piezoelectric transducer (“PZT”). The accelerometer66provides or generates a voltage that changes with force as the tire54rotates. Two forces that the accelerometer66experiences during tire rotation is centripetal force and earth's gravitational force. As the accelerometer66travels in a circle during one tire rotation, it will experience the earth's gravitation force change from +1G to −1G in a sinusoidal pattern over one rotation of the tire. The centripetal force will either be of a consistent level when the vehicle is traveling at a constant velocity, or will be slowly changing with vehicle speed, in comparison to the change in the earth's gravitational force during rotation.

The accelerometer sensor66is connected to an Analog-to-Digital Converter (“ADC”)64. The output of the ADC, representing the sampled acceleration signal, is connected to a low pass filter (“LPF”)70that can be embodied as hardware or the function accomplished in software. The LPF70aids in removing road noise from the accelerometer signal. The output of the LPF70is compared against a plus threshold value in comparator72and a minus threshold value in comparator74and provides a signal reference level for use in a data slicer76. The data slicer76converts the analog signal into a digital signal (0or1). Edge detector circuit78detects the rising and falling edge of the signal output from the accelerometer66so as to indicate a first predetermined angular position (a 0 value) and a second predetermined angular position (a 1 value) of the tire as the tire rotates. The signal processing of the acceleration signal is such that the 0 and 1 value that occurs at the first and second predetermined angular positions occur as angular position on the tire that are approximately 180 degrees apart. The output of the edge detector is connected to a microcomputer80. The LPF70, threshold comparators72,74, data slicer76, and edge detector function78could be embodied in software within the microcomputer80.

The tire-based sensor14further includes a tire condition sensor82for sensing tire pressure and/or tire temperature. The output of the tire condition sensor82is connected to a signal processor circuit84that converts the signal from the sensor82into a digital format and places the information into a digital packet or word for ultimate transmission having information regarding the sensed tire condition. The output of the signal processor84is connected to the microcomputer80.

The microcomputer80has stored in its internal memory its associated, unique ID, e.g., sensor ID=S1in this example. As mentioned, each tire has its associated unique tire ID. The microcomputer80assembles the digital information packet or word for transmission that includes the sensed tire condition and the associated ID. The microcomputer could include other data as part of the information packet if desired such as a wake-up portion, a check-sum portion, etc. The microcomputer, however, does not include as part of the information packet any angle information from the sensor66. The output of the microcomputer80is connected to an RF transmitter circuit86for transmission of the information packet having the tire condition information via antenna88.

The microcomputer80includes internal timers that control sample timing (monitoring timing of the sensor66and the tire condition sensor82) and controls transmission rate of information packets from the transmitter86. In one embodiment of the invention, the sensor66and tire condition sensor82could always be monitored and tire condition information transmitted each time the edge detector78indicates a 0 or 180 degree tire position has been reached during tire rotation. Such continuous sensing and transmission of data is not necessary. Also, Federal transmission guidelines (Federal Communications Commission) must be followed that, at the present, would not permit excessive data transmission.

Referring toFIG. 5, the operation of the vehicle-based receiver will be appreciated as well as the transmission control followed by the tire-based sensor14. The vehicle-based receiver/controller44is connected to the output of the ABS ECU40via an appropriate connection such as the vehicle's controller-area network bus (“CAN-bus”). The vehicle-based receiver/controller44monitors the angular position of each of the wheels of the vehicle via the sensor32and toothed disc30associated with each wheel, i.e., monitors each of the wheel speed sensors22,24,26,28also designated as WS FR, WS FL, WS RR, and WS RL, respectively. The vehicle-based unit44also includes an RF receiver90connected to the antenna46for receiving and demodulating the tire condition information from each of the transmitters associated with the tire-based sensors14,16,18, and20.

The received signals from each of the tire-based units is referred to herein as message1when the wheel or tire rotation is at the first position and message2when the wheel or tire rotation is at the second position, which is approximately 180 degrees from the first position, as sensed by the sensor66.

An event graph92represents the occurrence of received tire condition signals from one of the tire-based unit14ID S1. When each tire condition signal is received, the receiver/controller44monitors the angular position of each of the four wheels as indicated by each associated ABS wheel speed sensor22,24,26, and28. The tables94are the angle values in degrees for the four wheels as detected by the ABS wheel speed sensor each time an RF tire condition message is received. These angular values are stored in memory as the angle values that occurred when a message was received having a tire ID=S1. Similarly, the wheel positions are stored for each of the tire-based units S2, S3and S4each time an RF signal from one of their associated tire condition sensors is received.

The transmission of the signals from each tire based unit, as mentioned, is controlled by the sensor's microcomputer80. The microcontroller80“knows” when tire rotation is occurring from the signal60from the sensor66. During a first ten minute period after initial tire rotation begins, it may be desirable to transmit a tire condition signal forty times. During forty predetermined time slots over the ten minute period, the microcontroller80monitors the tire condition sensor82and transmits a tire condition signal when the edge detector indicates the tire has reached the 0 or 180 degree position. The microcomputer can transmit the tire condition signal in any of several patterns in response to the 0 and 180 degree positions being reached during tire rotation. For example, the microcomputer can transmit at a first of the forty time slots when the tire position reaches position 1. During the second of the forty time slots, the microcontroller could wait and transmit when the tire position reaches position 2, and so on. The result would be tables94having a tire transmission pattern of 1, 2, 1, 2, etc. Any other desired pattern could be used by the microcomputer80. After a first 10 minute time interval of forty transmissions, the microcontroller could change the transmission timing to one time every minute. Also, the microcontroller can either maintain the same transmission pattern or could change the transmission pattern.

The receiver/controller44, after a sufficient amount of data is collected (sufficient numbers of tables94are filled), determines which tire angular positions correlate the best with having received tire condition signals that would have occurred at 0 and 180 degree positions. Assume that the microcontroller80was controlling the transmitter86to transmit in a 1, 2, 1, 2, pattern. Also assume that the table94indicates that that the FR ABS wheel speed sensor (WS FR) always measured angles 102 and 282 degrees, respectively, each time a tire condition signal had a S1ID. Then, the receiver could assume that the tire ID S1is located at the FR corner of the vehicle. Once tire condition data correlates with tire angular position with a confidence level above a predetermined threshold, that tire ID for that tire location is stored in an internal memory of the receiver/controller44for later use in identifying the tire location when tire condition information is to be displayed on the display48, e.g., an under inflated tire occurrence. The confidence level can be determined by several different methods. One example is to determine that the WS angle data in a table does not vary over a predetermined number of samples by more than a predetermined amount.

Once the sensor ID's are correlated with the corner locations, the pressure/temperature information portion of the transmitted signal is monitored for each of the sensors, and the tire condition information can be displayed along with the associated determined tire location information for the vehicle operator. As those skilled in the art will appreciate, the display of tire condition information can be limited only to abnormal tire conditions or can be continuous tire pressure and temperature information if so desired.

Referring toFIG. 6, a flow chart is shown depicting a control process150in accordance with an example embodiment of the present invention for determining tire location in a TPM system. The process starts at step152where initial conditions, flags, appropriate values, etc., are set. At step154, the ABS signals indicative of the wheel angular position from each of the vehicle tires is continuously captured and provided to the receiver/controller44. In step156, the receiver/controller44monitors for received RF tire condition information signals from the tire-based units. In step158, a determination is made whether RF signals have been received. If negative, the process loops back to step154where wheel angular position from the ABS wheel speed sensors is continued to be captured. If the determination in step158is affirmative, the wheel angles from all four wheels are temporarily stored in step160(table94). In step162, a determination is made as to whether there has been a sufficient amount of data collected to make a location determination. For example, it may be desired to have 10-20 samplings of data before a location determinations is made. If there is not enough data, the process loops back to step154until a sufficient amount of data is received and stored.

In step164, a determination of wheel location is performed by correlating the angular wheel position that best corresponds to the event of the received tire condition signals, e.g., wheel FR rotates 180 degrees each time a tire condition signal having S1ID is received therefore correlating S1with the FR location. In step166, a determination is made as to whether the determined tire location correlation has a confidence value greater than a predetermined value. Assuming that the confidence level of the determination is sufficient, the tire-based unit ID and determined tire location information is stored in memory in step168. If the confidence value is not greater than a predetermined level, no location information is stored, the process loops back to step154, and any previous stored location information is retained. The vehicle-based unit44correlates the sensors S1, S2, S3, and S4with tire locations FR, FL, RR, and RL on the vehicle.

Signal filtering is required even on smooth road surfaces. Both passive and adaptive digital filtering techniques can be used to smooth the signal over the frequency range of three to twenty Hertz without undue signal attenuation or use of battery energy.

From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. For example, although the toothed disc, as described in the example embodiment, has a missing tooth to establish a zero position of the wheel, the wheel position at the time the vehicle is started can be designated the zero position, knowing that every 72 pulses (assuming a disc with 72 teeth) returns the wheel to the “zero” position (i.e., start position). Also, it is contemplated that the tire-based sensors could communicate via RF to the ABS ECU and that the ABS ECU could perform the correlation of tire-based units with vehicle corner location. Such improvements, changes, and/or modifications within the skill of the art are intended to be covered by the appended claims.