JP2015063203A - Tire air-pressure monitoring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tire air-pressure monitoring apparatus capable of preventing turn-on of a warning lamp during auto-location, in a case that a correct air-pressure adjustment is performed after tire rotation in a front-rear different-pressure vehicle in which a recommended air pressure of a tire air-pressure is different between front and rear wheels.SOLUTION: A TPMSCU (Tire Pressure Monitoring System Control Unit) 4 includes a lamp turn-on control part 4a for changing a front-wheel-side turn-on threshold and a rear-wheel-side turn-on threshold to given values lower than the aforementioned thresholds during auto-location implementation.

Description

  The present invention relates to a tire pressure monitoring device.

  Patent Document 1 discloses a technique in which when a tire air pressure is reduced by a predetermined percentage from a recommended air pressure, a warning lamp is turned on to prompt the driver to travel at the recommended air pressure.

JP 2008-126959 A

However, in the above prior art, when the driver adjusts each tire air pressure after tire rotation in a vehicle with different recommended air pressures for the front and rear wheels, auto-location for updating the correspondence between each sensor unit and the wheel position is completed. In the meantime, since the warning lamp is lit, there is a problem that the driver feels uncomfortable.
An object of the present invention is a tire capable of preventing a warning lamp from being turned on during auto-location in a vehicle with different front and rear pressures having different recommended tire pressures when the appropriate air pressure is adjusted after tire rotation. The object is to provide a pneumatic monitoring device.

  In order to achieve the above object, in the present invention, the front wheel side lighting threshold value and the rear wheel side lighting threshold value are changed to predetermined values lower than both during the auto location.

  Therefore, it is possible to prevent the warning lamp from being turned on during auto location.

1 is a configuration diagram of a tire air pressure monitoring device of Example 1. FIG. 1 is a configuration diagram of a TPMS sensor 2 of Example 1. FIG. It is a control block diagram of TPMSCU4 for implementing wheel position determination control. 3 is a diagram showing a method for calculating the rotational position of each wheel 1. FIG. It is a figure which shows the calculation method of a dispersion | distribution characteristic value. 3 is a flowchart illustrating a flow of wheel position determination control processing according to the first embodiment. It is a flowchart which shows the flow of the warning lamp incorrect lighting prevention control process implemented in the lamp lighting control part 4a of Example 1. FIG. It is a figure which shows the relationship between the rotation position (the number of teeth of a rotor) of each wheel 1FL, 1FR, 1RL, and 1RR when the rotation position of the TPMS sensor 2FL of the left front wheel 1FL becomes the highest point and the number of receptions of TPMS data . It is a figure which shows the change of the dispersion characteristic value X according to the frequency | count of reception of TPMS data. It is a time chart which shows the motion of each threshold value by warning lamp incorrect lighting prevention control of Example 1. FIG. It is explanatory drawing which shows the incorrect lighting prevention effect | action of the warning lamp 6 of Example 1. FIG.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described using embodiments based on the drawings.
[Example 1]
[System configuration]
FIG. 1 is a configuration diagram of a tire pressure monitoring apparatus according to the first embodiment. In the figure, FL at the end of each symbol indicates a left front wheel, FR indicates a right front wheel, RL indicates a left rear wheel, and RR indicates a right rear wheel. In the following description, the description of FL, FR, RL, and RR is omitted when there is no need to explain them individually.
The tire pressure monitoring device of the first embodiment includes a TPMS (Tire Pressure Monitoring System) sensor 2, a receiver 3, a TPMS control unit (TPMSCU) 4, a display 5, a warning lamp 6, a wheel speed sensor 7, Is provided. The TPMS sensor 2 is attached to each wheel 1, and the receiver 3, the TPMSCU 4, the display 5, the warning lamp 6, and the wheel speed sensor 7 are provided on the vehicle body side.

The TPMS sensor 2 is attached to an air valve (not shown) position of the tire. FIG. 2 is a configuration diagram of the TPMS sensor 2 according to the first embodiment. The TPMS sensor 2 includes a pressure sensor (tire pressure detection means) 2a, a temperature sensor 2b, an acceleration sensor (G sensor) 2c, a sensor control unit (sensor CU) 2d, a transmitter 2e, and a button battery 2f. Prepare.
The pressure sensor 2a detects tire air pressure [kPa].
The temperature sensor 2b detects the temperature [° C.] of the air in the tire.
The G sensor 2c detects centrifugal acceleration [G] acting on the tire.
The sensor CU2d is operated by electric power from the button battery 2f, and includes a tire pressure information detected by the pressure sensor 2a, a temperature information in the tire detected by the temperature sensor 2b, and a TPMS including a sensor ID (identification information). Data is transmitted from the transmitter 2e by radio signal.
The sensor CU2d compares the centrifugal acceleration detected by the G sensor 2c with a preset traveling determination threshold value, and determines that the vehicle is stopped when the centrifugal acceleration is less than the traveling determination threshold value, and determines TPMS data. Stop sending On the other hand, if the centrifugal acceleration is equal to or greater than the travel determination threshold, it is determined that the vehicle is traveling, and TPMS data is transmitted at a predetermined timing.
The receiver 3 receives and decodes the radio signal output from each TPMS sensor 2, and outputs it to the TPMSCU 4.

TPMSCU4 reads each TPMS data, refers to the correspondence between each sensor ID and each wheel position stored in advance in the internal memory from the sensor ID of the TPMS data, and corresponds to which wheel position the TPMS data corresponds to The tire pressure contained in the TPMS data is displayed on the display 5 as the corresponding wheel position air pressure. TPMSCU4 also turns on the warning lamp 6 to warn of a decrease in air pressure when the tire pressure drops below a predetermined ratio (for example, 20%) with respect to the recommended air pressure, and displays the corresponding wheel position at a low pressure. And encourage the driver to drive at the appropriate air pressure. The lighting of the warning lamp 6 and the low pressure display of the reduced pressure wheel are performed by the lamp lighting control unit (lamp lighting means) 4a of the TPMSCU 4.
In Example 1, the placard pressure of the front wheel is 500 [kPa], the placard pressure of the rear wheel is 300 [kPa], the front wheel side lighting threshold for lighting the warning lamp 6 is 400 [kPa], and the rear wheel side lighting threshold is set to The front wheel side turn-off threshold to be turned off after the warning lamp 6 is turned on is set to 460 [kPa], and the rear wheel side turn-off threshold is set to 276 [kPa]. Plakat pressure is the recommended air pressure when the tire is cold. The turn-off threshold is 12% higher than the turn-on threshold by the placard pressure. Here, since the pressure of the tire rises according to the temperature, even if each threshold is changed based on Boyle-Charles's law according to the temperature of the air in the tire [° C.] obtained from the temperature sensor 2b. good. Alternatively, each threshold value may be arbitrarily set by the driver, but in the following description, each threshold value is set to the above-described constant value for simplicity.
The wheel speed sensor 7 is provided corresponding to each wheel, detects the wheel speed of the corresponding wheel, and outputs a wheel speed pulse corresponding to the wheel speed. TPMSCU4 calculates the traveling speed (vehicle speed) of the vehicle from each wheel speed pulse.

[Auto location]
As described above, TPMSCU4 determines which wheel data the received TPMS data is based on the correspondence between each sensor ID stored in the internal memory and each wheel position. When tire rotation is performed at the time of OFF, the correspondence relationship between each stored sensor ID and each wheel position does not match the actual correspondence relationship, and it is impossible to know which wheel data the TPMS data is. Here, “tire rotation” refers to changing the mounting position of the tire in order to make the tire tread wear uniform and extend the life (tread life). For example, in a passenger car, the left and right tire positions are generally crossed to replace the front and rear wheels.
Therefore, in Example 1, in order to register the correspondence between each sensor ID and each wheel position after tire rotation by storing and updating in the memory, if there is a possibility that tire rotation has been performed, each of the TPMSCU4 side Autolocation is performed to determine which wheel the TPMS sensor 2 belongs to. The TPMSCU 4 includes an auto location execution unit (auto location means) 4b that performs auto location.

[Position transmission mode]
The sensor CU2c of the TPMS sensor 2 determines that there is a possibility that tire rotation has been performed when the vehicle stop determination time immediately before the start of traveling is a predetermined time (for example, 15 minutes) or more.
When the vehicle stop determination time immediately before the start of traveling is less than the predetermined time, the sensor CU2c performs the “normal mode” in which TPMS data is transmitted at regular intervals (for example, 1 minute intervals). On the other hand, when the vehicle stop determination time is equal to or longer than the predetermined time, it is an interval shorter than the transmission interval in the normal mode (for example, about 16 seconds interval), and transmits TPMS data at a constant rotational position. Is implemented. The fixed position transmission mode is performed until the number of transmissions of the TPMS data reaches a predetermined number (for example, 40 times). When the number of transmissions reaches the predetermined number, the mode shifts to the normal mode. If it is determined that the vehicle has stopped before the number of transmissions of the TPMS data reaches the predetermined number, if the vehicle stop determination time is less than the predetermined time (15 minutes), the fixed position transmission before the vehicle stops until the number of transmissions reaches the predetermined number The mode is continued, and when the vehicle stop determination time is a predetermined time or longer, the continuation of the fixed position transmission mode before the vehicle is stopped is canceled and the fixed position transmission mode is newly started.

  The sensor CU2c determines the transmission timing of the TPMS data in the fixed position transmission mode based on the gravitational acceleration dependent component of the centrifugal acceleration detected by the G sensor 2c during the fixed position transmission mode. The centrifugal acceleration acting on the TPMS sensor 2 changes with the acceleration / deceleration of the wheel 1, but its gravitational acceleration dependent component is always constant, +1 [G] at the highest point and -1 [G] at the lowest point The waveform which is 0 [G] at a position of 90 degrees with respect to the uppermost point and the lowermost point is shown. That is, the rotational position of the TPMS sensor 2 can be grasped by monitoring the magnitude and direction of the gravitational acceleration component of the centrifugal acceleration. Therefore, for example, by outputting TPMS data at the peak of the gravity acceleration dependent component, TPMS data can always be output at the highest point.

[Auto location mode]
When the ignition switch is turned on, the auto-location execution unit 4b determines that the tire rotation may have been performed if the elapsed time from the ignition switch being OFF is a predetermined time (for example, 15 minutes) or more. .
When the ignition switch is turned ON and the elapsed time from OFF to ON of the ignition switch is less than a predetermined time, the auto-location execution unit 4b determines each of the values based on the air pressure information of the TPMS data transmitted from each TPMS sensor 2. Implement “Monitor Mode” to monitor the tire 1 tire pressure. On the other hand, when the elapsed time from the ignition switch to the ON is equal to or longer than the predetermined time, the “auto location mode” for determining the wheel position of each TPMS sensor 2 is performed. The auto location mode is performed until the wheel positions of all the TPMS sensors 2 are determined. When the wheel positions of all the TPMS sensors 2 are determined, the monitor mode is entered.

Note that even during the auto location mode, the tire pressure can be monitored from the air pressure information included in the TPMS data. Based on the relationship, the display 5 displays the air pressure and the warning lamp 6 warns of a decrease in air pressure.
The TPMSCU 4 inputs the count value of the wheel speed pulse from the wheel speed sensor 7 during the auto location mode, and performs the wheel position determination control as described below.

[Wheel position determination control]
FIG. 3 is a control block diagram of the TPMSCU 4 for performing wheel position determination control. The TPMSCU 4 includes a rotation position calculation unit (rotation position detection means) 4c, a dispersion calculation unit 4d, a wheel position determination unit 4e, And a memory 4f.
The rotational position calculation unit 4c inputs the decoded TPMS data output from the receiver 3 and the count value of each wheel speed pulse output from the wheel speed sensor 7, and the rotational position of each TPMS sensor 2 is the highest point. The rotational position (number of teeth of the rotor) of each wheel 1 is calculated. Here, the “number of teeth of the rotor” indicates which tooth of the rotor is counted by the wheel speed sensor 7, and the count value of the wheel speed pulse is counted for one rotation of the tire (= 1 rotation). The number of teeth z = 48) can be obtained by division. In Example 1, when the count value of each wheel speed pulse for the first time was entered after starting the auto location mode, the value obtained by adding 1 to the remainder obtained by dividing the count value by the number of teeth for one rotation is the reference tooth number. In the second and subsequent times, the number of teeth is determined based on the number of wheel speed pulses counted from the reference number of teeth (current count value minus the first count value).

FIG. 4 is a diagram showing a method for calculating the rotational position of each wheel 1.
In FIG. 4, the time when the count value of the wheel speed pulse is input is t1, the time when the rotational position of the TPMS sensor 2 is the highest point is t2, and the time when the TPMS sensor 2 actually starts transmitting TPMS data. t3, the time when TPMSCU4 completes the reception of TPMS data is t4, and the time when the wheel speed pulse count value is input is t5. At this time, t1, t4, t5 can be actually measured, t3 can be calculated by subtracting the data length of TPMS data (specified value, for example, about 10 msec) from t4, and t2 is a time lag at the time of transmission from t3 ( It can be calculated in advance by experiments etc.).
Therefore, if the number of teeth at _t1 is z _t1 , the number of teeth at _t2 is z _t2 , and the number of teeth at _t5 is z _t5 ,
(t2-t1) / (t5-t1) = (z _t2 -z _t1 ) / (z _t5 -z _t1 )
Is established,
z _t2 -z _t1 = (z _t5 -z _t1 ) * (t2-t1) / (t5-t1)
Therefore, the number of teeth z _{t2 at} time t2 when the rotational position of the TPMS sensor 2 becomes the highest point is
z _t2 = z _t1 + (z _t5 -z _t1 ) * (t2-t1) / (t5-t1)
It becomes.

The dispersion calculation unit 4d accumulates the rotation position of each wheel 1 calculated by the rotation position calculation unit 4c for each sensor ID to obtain rotation position data. The dispersion characteristic value indicates the degree of variation of each rotation position data for each sensor ID. Calculate as The calculation of the dispersion characteristic value is performed every time the rotation position of the same sensor ID is calculated by the rotation position calculation unit 4c.
FIG. 5 is a diagram showing a method for calculating the dispersion characteristic value. In the first embodiment, a unit circle (circle having a radius of 1) centered on the origin (0,0) is considered on each two-dimensional plane, and each wheel is considered. 1 rotation position θ [deg] (= 360 × number of teeth of rotor / 48) is converted into coordinates (cosθ, sinθ) on the circumference of the unit circle. That is, the rotational position of each wheel 1 is regarded as a vector of length 1 with the origin (0,0) as the start point and the coordinates (cosθ, sinθ) as the end point, and the average vector (ave_cosθ, ave_sinθ) is calculated, and the scalar quantity of the average vector is calculated as the dispersion characteristic value X of the rotational position data.
(cosθ, sinθ) = (cos ((z _t2 +1) * 2π / 48), sin ((z _t2 +1) * 2π / 48))
Therefore, if the number of receptions of TPMS data of the same sensor ID is n (n is a positive integer), the average vector (ave_cosθ, ave_sinθ) is
(ave_cosθ, ave_sinθ) = ((Σ (cosθ)) / n, (Σ (sinθ)) / n)
The dispersion characteristic value X is
X = ave_cosθ ² + ave_sinθ ²
Can be expressed as

  The wheel position determination unit 4e compares the dispersion characteristic value X of each rotational position data of the same sensor ID calculated by the dispersion calculation unit 4d, and the maximum value of the dispersion characteristic value X is the first threshold value (for example, 0.57). And the remaining three dispersion characteristic values X are all less than the second threshold value (for example, 0.37), the wheel position of the rotational position data corresponding to the maximum dispersion characteristic value X, That is, the wheel position of the wheel speed sensor 7 that has detected the rotational position data is determined as the wheel position of the TPMS sensor 2 corresponding to the sensor ID of the rotational position data. By carrying out this determination for all sensor IDs, the correspondence between each sensor ID and each wheel position is obtained and registered by updating the memory 4f.

[Wheel position determination control processing]
FIG. 6 is a flowchart showing the flow of the wheel position determination control process according to the first embodiment, and each step will be described below. In the following description, the case of sensor ID = A will be described, but the wheel position determination control process is also performed in parallel for other IDs (ID = B, C, D).
In step S1, the rotational position calculation unit 4c receives TPMS data of sensor ID = A.
In step S2, the rotational position calculation unit 4c calculates the rotational position of each wheel 1.
In step S3, the dispersion characteristic value X of the rotational position data of each wheel 1 is calculated in the dispersion calculation unit 4d.
In step S4, it is determined whether or not the TPMS data of sensor ID = A has been received a predetermined number of times (for example, 10 times) or more. If YES, the process proceeds to step S5, and if NO, the process returns to step S1.
In step S5, in the wheel position determination unit 4e, whether or not the maximum dispersion characteristic value is larger than the first threshold value 0.57 and the remaining dispersion characteristic value is less than the second threshold value 0.37. If YES, the process proceeds to step S6. If NO, the process proceeds to step S7.

In step S6, the wheel position determination unit 4e determines that the wheel position of the rotational position data corresponding to the highest dispersion characteristic value is the wheel position of the sensor ID, and ends the auto location mode.
In step S7, the wheel position determination unit 4e determines whether or not a predetermined cumulative travel time (for example, 8 minutes) has elapsed since the start of the auto location mode. If YES, the process proceeds to step S8. If NO, the auto location mode is terminated.
If the wheel positions can be determined for all the sensor IDs within the predetermined cumulative travel time, the wheel position determination unit 4e registers the correspondence between each sensor ID and each wheel position by storing and updating the memory 4f. On the other hand, when the wheel positions cannot be determined for all the sensor IDs within the predetermined cumulative travel time, the correspondence relationship between each sensor ID and each wheel position currently stored in the memory 4f is continuously used.

[Warning lamp false lighting prevention control]
TPMSCU4 switches from monitor mode to autolocation mode to prevent the warning lamp 6 from being lit in error during autolocation even though the correct air pressure is adjusted after tire rotation When this happens, the warning lamp erroneous lighting prevention control as shown below is performed until the auto-location mode ends. The warning lamp erroneous lighting prevention control is performed by the lamp lighting control unit 4a of the TPMSCU 4. In order to realize the warning lamp mislighting prevention control, the TPMSCU4 stores the lighting state of the warning lamp 6 and the most recently received tire pressure of each wheel and the air temperature in the tire each time the ignition switch is turned off. To remember.

FIG. 7 is a flowchart showing a flow of a warning lamp erroneous lighting prevention control process performed by the lamp lighting control unit 4a of the first embodiment. Each step will be described below.
In step S11, it is determined whether or not auto-location has started. If YES, the process proceeds to step S12. If NO, the process proceeds to return.
In step S12, the front wheel side lighting threshold and the rear wheel side lighting threshold are changed to predetermined values lower than both. Here, the predetermined value is a tire air pressure at which the vehicle can travel at least until the tire is not punctured and at least the auto-location is completed. The predetermined value may be changed based on Boyle-Charles' law according to the temperature of the air in the tire, as in the case of each threshold. In the first embodiment, the predetermined value is set to 150 [kPa]. This value is the tire pressure at which the vehicle can travel even when the tire is cold.
In step S13, it is determined whether or not the tire pressure of at least one wheel is lower than the lighting threshold 150 [kPa]. If YES, the process proceeds to step S14, and if NO, the process proceeds to step S15.
In step S14, the warning lamp 6 is turned on, and the low-pressure wheel is displayed at a low pressure.

In step S15, it is determined whether or not the wheel, which has been displayed at low pressure when the ignition switch is OFF, is higher than the turn-off threshold (front wheel 460 [kPa], rear wheel 276 [kPa]). If YES, the process proceeds to step S16. If NO, the process proceeds to step S17.
In step S16, the low pressure display of the pneumatic return wheel is turned off.
In step S17, the low pressure display of the wheel with the air pressure lowered is turned on.
In step S18, it is determined whether or not the low pressure display of all four wheels is turned off. If YES, the process proceeds to step S19, and if NO, the process proceeds to step S20.
In step S19, the warning lamp 6 is turned off.
In step S20, it is determined whether or not auto-location has ended. If YES, the process proceeds to step S21, and if NO, the process returns to step S13.
In step S21, each threshold value is reset according to the wheel position determination result by autolocation, that is, the relationship between the updated sensor ID of each TPMS sensor 2 and the wheel position. That is, the lighting threshold of the TPMS sensor 2 in which the wheel position is determined to be the front wheel is set to 400 [kPa], the lighting threshold is set to 460 [kPa], and the lighting threshold of the TPMS sensor 2 in which the wheel position is determined to be the rear wheel is set to 240 [kPa], set the extinction threshold to 276 [kPa].

Next, the operation will be described.
[Wheel position determination function based on variation in rotational position data]
Each TPMS sensor 2 determines that there is a possibility that tire rotation has been performed when the vehicle stop determination time immediately before the start of travel is 15 minutes or more, and shifts from the normal mode to the fixed position transmission mode. In the fixed position transmission mode, each TPMS sensor 2 transmits TPMS data when 16 seconds have elapsed from the previous transmission time and its own rotational position is at the highest point.

  On the other hand, TPMSCU4 shifts from the monitor mode to the auto-learning mode when the elapsed time from the ignition switch OFF to ON is 15 minutes or more. In auto-learning mode, every time TPMSCU4 receives TPMS data from each TPMS sensor 2, the rotational position of the TPMS sensor 2 is the highest point from the input time of the count value of the wheel speed pulse, the reception completion time of the TPMS data, etc. The rotational position (number of teeth of the rotor) of each wheel 1 is calculated, and this is repeated 10 times or more and accumulated as rotational position data. The rotational position data with the smallest variation among the rotational position data is calculated. The corresponding wheel position is determined as the wheel position of the TPMS sensor 2.

  When the vehicle travels, the rotational speed of each wheel 1 varies depending on the difference between the inner and outer wheels when turning, the locking and slipping of the wheel 1, and the tire pressure difference. It is known that even during straight running, there is a difference in rotational speed between the front and rear wheels 1FL and 1FR and between the left and right wheels 1RL and 1RR due to a slight correction rudder by the driver and a difference in the left and right road surface conditions. In other words, the rotational speed of each wheel 1 varies depending on the running, whereas the TPMS sensor 2 and the wheel speed sensor 7 (the rotor teeth) rotate together, so that the output cycle of a certain TPMS sensor 2 On the other hand, the output cycle of the wheel speed sensor 7 of the same wheel is always synchronized (matched) regardless of the travel distance and the travel state.

Therefore, the wheel position of each TPMS sensor 2 can be accurately determined by looking at the degree of variation in the rotational position data of each wheel 1 with respect to the transmission cycle of the TPMS data.
Fig. 8 shows the relationship between the rotational position of each wheel 1FL, 1FR, 1RL, 1RR (number of teeth on the rotor) and the number of TPMS data received when the rotational position of the TPMS sensor 2FL on the left front wheel 1FL is the highest point. (A) is the wheel speed sensor 7FL for the left front wheel 1FL, (b) is the wheel speed sensor 7FR for the right front wheel 1FR, (c) is the wheel speed sensor 7RL for the left rear wheel 1RL, and (d) is the right Corresponds to the wheel speed sensor 7RR of the rear wheel 1RR.
As is clear from FIG. 8, the wheel positions (number of teeth) obtained from the wheel speed sensors 7FR, 8RL, 8RR of the other wheels (right front wheel 1FR, left rear wheel 1RL, right rear wheel 1RR) have a large degree of variation. On the other hand, the wheel position obtained from the wheel speed sensor 7FL of the own wheel (the left front wheel 1FL) has the smallest degree of variation, and the output cycle of the TPMS sensor 2FL and the output cycle of the wheel speed sensor 7FL are almost synchronized.
In the wheel position determination control according to the first embodiment, the wheel position of each TPMS sensor 2 can be determined without using the radio wave intensity. Therefore, the wheel position of each TPMS sensor 2 can be determined regardless of the reception environment and layout. Further, since only one receiver 3 is required, the cost can be kept low.

[Effect of variation degree judgment by dispersion characteristic value]
Since the rotational position of wheel 1 is periodic angle data, the degree of variation in rotational position cannot be determined from the general variance formula defined by the average of the square of the difference from the average. .
Therefore, in the first embodiment, in the variance calculation unit 4d, the rotational position θ of each wheel 1 obtained from each wheel speed sensor 7 is set to the coordinates on the circumference of the unit circle around the origin (0, 0) ( cosθ, sinθ), the coordinates (cosθ, sinθ) are regarded as vectors, the average vector (ave_cosθ, ave_sinθ) of each vector of the same rotational position data is obtained, and the scalar quantity of the average vector is calculated as the dispersion characteristic value X Thus, the degree of variation in rotational position can be obtained while avoiding periodicity.

FIG. 9 is a diagram illustrating a change in the dispersion characteristic value X according to the number of receptions of TPMS data. In FIG. 9, the own wheel shows the dispersion characteristic value X calculated from the rotational position data of the wheel speed sensor 7 of the same wheel as the TPMS sensor 2 that transmitted the TPMS data, and the other wheel is different from the TPMS sensor 2 that transmitted the TPMS data. The dispersion characteristic value X calculated from the rotational position data of the wheel speed sensor 7 of the wheel 1 is shown.
As shown in FIG. 9, the dispersion characteristic value X of the own wheel approaches 1 and the dispersion characteristic value X of the other wheel approaches 0 as the number of receptions of TPMS data of the same sensor ID increases. Therefore, it is sufficient to select the maximum dispersion characteristic value X (dispersion characteristic value X closest to 1) when the sufficient number of receptions (several tens of times) is reached, but the wheel immediately after the tire rotation is performed. Since it is impossible to notify the driver of accurate tire information during position determination, a delay in determination time is not preferable. On the other hand, when the number of receptions is small (about several times), there is no difference in the dispersion characteristic value X between the own wheel and the other wheel, resulting in a decrease in determination accuracy.

Therefore, in the first embodiment, when the wheel position determination unit 4e receives TPMS data of the same sensor ID 10 times or more, the dispersion characteristic value X of each rotational position data of the sensor ID is compared, and the dispersion characteristic value X When the maximum value is greater than the first threshold value 0.57 and the remaining three dispersion characteristic values X are all less than the second threshold value 0.37, the rotation corresponding to the maximum dispersion characteristic value X The wheel position of the position data is determined as the wheel position of the sensor ID.
Rather than simply selecting the maximum value of the dispersion characteristic value X, a certain determination accuracy can be ensured by comparing the maximum value with the first threshold value (0.57). Furthermore, by comparing the dispersion characteristic value X other than the maximum value with the second threshold value (0.37), it can be confirmed that there is a difference of more than the predetermined value (0.2) between the maximum value and the other three values. Can be further enhanced. For this reason, it is possible to achieve both of ensuring the determination accuracy and shortening the determination time with a small number of receptions of 10 times.

[Lighting threshold change effect]
FIG. 10 is a time chart showing the movement of each threshold value by the warning lamp erroneous lighting prevention control of the first embodiment. Here, the sensor IDs of the TPMS sensor 2 of the left front wheel 1FL, the right front wheel 1FR, the left rear wheel 1RL, and the right rear wheel 1RR before tire rotation are A, B, C, and D, and the left front wheel 1FL and the right rear are rotated by the tire rotation. It is assumed that the wheel 1RR is replaced and the right front wheel 1FR and the left rear wheel 1RL are replaced.
Wheels corresponding to sensor ID = A, B before tire rotation, that is, the lighting threshold of the left and right front wheels 1FL, 1FR is 400 [kPa], the extinguishing threshold is 460 [kPa], the wheels corresponding to sensor ID = C, D, The lighting threshold values of the left and right rear wheels 1RL and 1RR are 240 [kPa] and the lighting threshold value is 276 [kPa].

At time t1, the ignition switch is turned on, and autolocation starts when it is determined that there is a possibility of tire rotation. At this time, the lamp lighting control unit 4a changes the lighting threshold values of all the sensor IDs to the same predetermined value 150 [kPa]. On the other hand, the lighting threshold value maintains the value before auto location.
At time t2, since the auto-location is completed, the lamp lighting control unit 4a sets the wheel lighting threshold value and the light-off threshold value corresponding to each sensor ID based on the correspondence relationship between each sensor ID and the wheel position updated by the auto location. Reset it. In auto-location, the wheels corresponding to sensor ID = A, B, C, D are judged as right rear wheel 1RR, left rear wheel 1RL, right front wheel 1RR, left front wheel 1FL, so it corresponds to sensor ID = A, B Set the lighting threshold of the left and right rear wheels 1RL and 1RR to 240 [kPa], the extinguishing threshold to 276 [kPa], and the wheels corresponding to the sensor ID = C and D, that is, the lighting threshold of the left and right front wheels 1FL and 1FR Is set to 400 [kPa], and the turn-off threshold is set to 460 [kPa].

[Warning lamp warning light prevention action]
As shown in FIG. 11 (a), the vehicle according to the first embodiment is a front / rear differential pressure vehicle in which the recommended air pressure for the front and rear wheels is set to 500 [kPa] and the recommended air pressure for the rear wheels is set to 300 [kPa]. The side lighting threshold (recommended air pressure x 80%) is 400 [kPa], and the rear wheel lighting threshold is 240 [kPa]. Here, as in the case of FIG. 10, the sensor IDs of the TPMS sensors 2 of the left front wheel 1FL, the right front wheel 1FR, the left rear wheel 1RL, and the right rear wheel 1RR before tire rotation are A, B, C, and D.
When the tire pressure before tire rotation is the recommended air pressure, when the driver performs tire rotation that crosses the left and right tire positions and swaps the front and rear wheels, the tire pressure of the left and right front wheels is insufficient for the recommended air pressure of 200 [kPa] Since the tire air pressure of the left and right rear wheels is 200 [kPa] higher than the recommended air pressure, the driver adjusts each tire air pressure to the recommended air pressure (FIG. 11 (b)).

After that, when the driver turns on the ignition switch and starts the vehicle, if the elapsed time from the ignition switch OFF to ON is longer than the predetermined time, the monitor mode is switched to the auto location mode. Since each tire pressure is continuously monitored even if the vehicle is in the middle, the correspondence relationship between each sensor ID currently stored and each wheel position (A = left front wheel, B = right front wheel, C = left rear wheel, D = Rear wheel), it is determined that the tire pressure of sensor ID = A, B is less than the front wheel side lighting threshold 400 [kPa].
At this time, in the conventional tire pressure monitoring device, the warning lamp is turned on until the correspondence between each sensor ID and the wheel position is updated by autolocation. Since the driver adjusts each tire pressure to the recommended pressure, lighting of the warning lamp gives the driver a feeling of strangeness. In the auto location of the first embodiment, the wheel position of each TPMS sensor 2 is determined from the degree of variation of each rotational position data. At this time, since the radio signal transmitted at 16-second intervals is acquired 10 times or more in order to improve the determination accuracy, the warning lamp continues to be lit for 160 seconds or more, and the driver feels uncomfortable.

On the other hand, in Example 1, when it is determined in step S1 that auto-location has started, in step S2, the front wheel side lighting threshold and the rear wheel side lighting threshold are both set to a predetermined value 150 [kPa] lower than both. change.
Therefore, as shown in FIG. 11 (b), when the driver properly adjusts the tire pressure after the tire rotation, the tire pressures of the four wheels exceed the predetermined value 150 [kPa]. Warning lamp 6 does not light up. As a result, the warning lamp 6 can be prevented from erroneously lighting for 160 seconds or more, and the uncomfortable feeling given to the driver can be reduced.

  In the first embodiment, the front wheel side lighting threshold value and the rear wheel side lighting threshold value are reduced to predetermined values during autolocation, while the front wheel side lighting threshold value and the rear wheel side lighting threshold value are set to the values before autolocation. maintain. As a result, when the warning lamp 6 was lit when the ignition switch was turned off the last time, and the driver made an appropriate air pressure adjustment for the warning after the ignition switch was turned off, the warning lamp 6 can be turned off. On the other hand, when the driver does not perform proper air pressure adjustment, the warning lamp 6 is lit during auto location, so the driver can be continuously urged to travel at the recommended air pressure. In this case, since the driver recognizes the decrease in air pressure, the driver does not feel uncomfortable even if the warning lamp 6 is turned on. That is, by disabling the lighting of the warning lamp 6 during auto-location only when the driver is taking appropriate measures, it is possible to prevent the driver from feeling uncomfortable.

  In the first embodiment, the lighting threshold values of the four wheels in the auto location mode are set to a predetermined value 150 [kPa] lower than the lighting threshold values in the monitor mode (front wheel 400 [kPa], rear wheel 240 [kPa]). Therefore, even if tire rotation is not performed and the tire pressure of the rear wheels is lower than 240 [kPa] while the vehicle is stopped, each tire pressure exceeds a predetermined value 150 [kPa] Warning lamp 6 does not light up. On the other hand, in the first embodiment, the lighting threshold value during auto-location is set to a predetermined value 150 [kPa] at which the vehicle can travel, so that the tire is punctured, that is, the tire air pressure is lower than the predetermined value 150 [kPa]. In this state, the warning lamp 6 can be prevented from being turned off. Further, since the warning lamp 6 is turned on when the auto-location is completed, the driver can be warned of a decrease in air pressure.

Next, the effect will be described.
The tire pressure monitoring device of the first embodiment has the following effects.
(1) A pressure sensor 2a that is mounted on the tire of each wheel 1 and detects the tire air pressure, and when the air pressure of the left and right front wheels 1FL, 1FR falls below the front wheel side lighting threshold 400 [kPa], or the rear wheel 1RL, When the air pressure of 1RR falls below the rear wheel side lighting threshold 240 [kPa], the lamp lighting control unit 4a that lights the warning lamp 6 and the ignition switch are turned on, and then each pressure sensor 2a (TPMS sensor 2) An autolocation execution unit 4b that performs autolocation to determine the wheel position of each of the pressure sensors 2a and update the correspondence relationship between each pressure sensor 2a and the wheel position, and the lamp lighting control unit 4a The side lighting threshold and the rear wheel lighting threshold are changed to a predetermined value 150 [kPa] lower than both.
As a result, when the tire air pressure is properly adjusted after the tire rotation, the warning lamp 6 is not lit during auto location, so that it is possible to prevent the driver from feeling uncomfortable.

(2) The lamp lighting control unit 4a is used when the air pressure of the left and right front wheels 1FL, 1FR falls below the front wheel side lighting threshold 400 [kPa] and then exceeds the front wheel side lighting threshold 460 [kPa]. If the rear wheel side turn-off threshold value 276 [kPa] is exceeded after the rear wheel side turn-on threshold value 240 [kPa] is exceeded, the warning lamp 6 is turned off and the front wheel side turn-off threshold value and the rear wheel side are turned off during auto-location. The extinguishing threshold value is maintained at a value immediately before the execution of the auto location.
As a result, when the driver is performing an appropriate process for reducing the air pressure, the warning lamp 6 is not lit during auto-location, so that the driver can be prevented from feeling uncomfortable. In addition, when the driver does not perform appropriate processing for the decrease in air pressure, the warning lamp 6 is lit during auto location, so the driver can be continuously urged to travel at the recommended air pressure.

(3) The lamp lighting control unit 4a sets the predetermined value as the tire pressure at which the vehicle can travel.
Thereby, it is possible to avoid the warning lamp 6 from being extinguished when the vehicle cannot travel due to tire puncture or the like.

(4) When the auto-location ends, the lamp lighting control unit 4a determines whether the left and right front wheels 1FL, 1FR are turned on and off and the left and right rear wheels according to the correspondence between the updated sensor ID of each TPMS sensor 2 and the wheel position. Reset the lighting and extinguishing thresholds of 1RL and 1RR.
As a result, even if the tire air pressure decreases between the time when the ignition switch is turned off and the time when the ignition switch is turned on, the warning lamp 6 is turned on when the autolocation is completed, so that the driver can be warned of the air pressure decrease.

(5) a transmitter 2e that is provided on each wheel 1 and transmits the air pressure by a wireless signal together with a unique sensor ID at a predetermined rotational position; a receiver 3 that is provided on the vehicle body side and receives the wireless signal; A wheel speed sensor 7 provided on the vehicle body side corresponding to each wheel 1 and detecting the rotational position of the wheel, and the autolocation execution unit 4b is configured to output each radio signal including a certain sensor ID. The rotational position of the wheel 1 is acquired 10 times or more and accumulated as rotational position data of each wheel 1, and the wheel position corresponding to the rotational position data with the smallest variation among the rotational position data is transmitted corresponding to the sensor ID. It is determined as the wheel position of the machine 2e.
Thereby, it is possible to accurately determine the wheel position of each transmitter 2e without using radio wave intensity and at low cost.

[Other Examples]
The best mode for carrying out the present invention has been described with reference to the embodiments based on the drawings. However, the specific configuration of the present invention is not limited to the embodiments, and does not depart from the gist of the invention. Such design changes are included in the present invention.
For example, in the embodiment, a vehicle having a front wheel lighting threshold larger than the rear wheel lighting threshold has been described. However, the present invention can also be applied to a vehicle having a rear wheel lighting threshold larger than the front wheel lighting threshold. An effect can be obtained.

1 wheel
2 TPMS sensor
2a Pressure sensor (Tire pressure detection means)
2b Temperature sensor
2c G sensor
2d sensor CU
2e transmitter
2f button battery
3 Receiver
4 TPMSCU
4a Lamp lighting control unit (lamp lighting means)
4b Auto-location implementation department (auto-location means)
4c Rotation position calculation unit (Rotation position detection means)
4d Distributed arithmetic unit
4e Wheel position judgment part
4f memory
5 display
6 Warning lamp
7 Wheel speed sensor

Claims (5)

Tire pressure detecting means mounted on the tire of each wheel and detecting the tire pressure;
When the front wheel air pressure falls below the front wheel side lighting threshold, or when the rear wheel air pressure falls below the rear wheel side lighting threshold different from the front wheel side lighting threshold, lamp lighting means for lighting a warning lamp;
After the ignition switch is turned on, auto location means for determining the wheel position of each tire air pressure detecting means and performing auto location for updating the correspondence between each tire air pressure detecting means and the wheel position;
With
The lamp lighting means changes the front wheel side lighting threshold and the rear wheel side lighting threshold to predetermined values lower than both during execution of the autolocation. In the tire pressure monitoring device according to claim 1,
The lamp lighting means, when the front wheel air pressure falls below the front wheel side lighting threshold value and then exceeds a front wheel side lighting threshold value higher than the front wheel side lighting threshold value, and the rear wheel air pressure exceeds the rear wheel side lighting threshold value. When the rear wheel side turn-off threshold value is higher than the rear wheel side turn-on threshold value after being lower, the warning lamp is turned off,
A tire pressure monitoring device that maintains the front wheel-side turn-off threshold and the rear wheel-side turn-off threshold at values immediately before the execution of the auto-location during the auto-location. In the tire pressure monitoring device according to claim 1 or 2,
The tire lighting monitor device characterized in that the lamp lighting means uses the predetermined value as a tire pressure at which a vehicle can travel. In the tire pressure monitoring device according to any one of claims 1 to 3,
The lamp lighting means resets each threshold value according to the correspondence relationship between each updated tire pressure detecting means and wheel position at the end of the autolocation. The tire pressure monitoring device according to any one of claims 1 to 4,
A transmitter that is provided on each wheel and that transmits the air pressure together with identification information unique to each transmitter at a predetermined rotational position;
A receiver provided on the vehicle body side for receiving the radio signal;
Rotation position detecting means provided on the vehicle body side corresponding to each wheel and detecting the rotation position of the wheel;
With
The auto-location means acquires the rotational position of each wheel when a wireless signal including certain identification information is output, and accumulates it as rotational position data of each wheel, and the degree of variation is the largest among the rotational position data. A tire air pressure monitor device that determines a wheel position corresponding to small rotational position data as a wheel position of a transmitter corresponding to the identification information.

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