JP5803555B2 - Wheel position detecting device and tire air pressure detecting device having the same - Google Patents

Description

  The present invention relates to a wheel position detection device that automatically detects in which position of a vehicle a target wheel is mounted, and in particular, a transmitter having a pressure sensor on a wheel to which a tire is attached. It is suitable to be applied to a direct tire pressure detection device that detects tire pressure by directly attaching and transmitting the detection result of the pressure sensor from the transmitter and receiving it by the receiver attached to the vehicle body side. .

  Conventionally, there is a direct type as one of tire pressure detecting devices. In this type of tire pressure detecting device, a transmitter equipped with a sensor such as a pressure sensor is directly attached to a wheel side to which a tire is attached. In addition, an antenna and a receiver are provided on the vehicle body side. When a detection signal from the sensor is transmitted from the transmitter, the detection signal is received by the receiver via the antenna, and tire pressure is detected. Done.

  In such a direct tire pressure detecting device, the data transmitted by the transmitter can be determined so that it can be determined whether the transmitted data belongs to the host vehicle and which wheel the transmitter is attached to. ID information for discriminating whether the vehicle is a host vehicle or another vehicle and discriminating a wheel to which a transmitter is attached is individually given.

  In order to specify the position of the transmitter from the ID information included in the transmission data, the ID information of each transmitter needs to be registered in advance on the receiver side in association with the position of each wheel. For this reason, at the time of tire rotation, it is necessary to re-register the transmitter ID information and the wheel positional relationship with the receiver.

  On the other hand, a trigger signal is transmitted from a trigger device provided for each transmitter to the transmitter, and data including ID information is transmitted from the transmitter to the receiver in synchronization with the transmission. There has been proposed a method of registering the ID information of a machine and the positional relationship of wheels with a receiver (see Patent Document 1). There has also been proposed a method of reading the barcode attached to each transmitter and registering the ID information of the transmitter in the receiver. However, these methods have a problem that the number of man-hours for ID registration increases and the cost increases due to an increase in the number of parts such as a trigger machine and a barcode reader. In addition, there is a problem that, during tire rotation, ID information registration work occurs and work efficiency deteriorates. For this reason, there is a need for a system that can automatically perform ID information registration work for a transmitter.

  In order to perform such automatic registration work, it is detected which of the left and right wheels using a biaxial acceleration sensor, and which of the front and rear wheels is detected based on the reception intensity of RF data. Thus, there is a method for detecting the tire positions of the four wheels (see Patent Document 2). In addition, the reception strength received by a plurality of antennas is cumulatively measured, and the position of the transmitter is determined based on the reception strength (see Patent Document 3), or the signal sent from the transmitter mounted on each wheel There is a method of determining the position of a transmitter based on a distribution of RSSI (Received Signal Strength Indicator) values (see Patent Document 4).

  Furthermore, a trigger signal is output from a trigger device provided on the vehicle body side, and the fact that the reception strength of the trigger signal changes according to the distance between the trigger device and each transmitter is used, based on the reception strength of the trigger signal. Some also specify the wheel position (see Patent Document 5).

Japanese Patent No. 3212311 US Pat. No. 7,010,968 US Pat. No. 6,018,993 US Pat. No. 6,489,888 JP 2007-15491 A

  However, in the method described in Patent Document 2, the RSSI value of the RF data from the transmitter is compared or the number of receptions is compared in order to determine which of the front and rear wheels is. Comparison results are not always the same. For example, the transmission output level of the transmitter may vary due to product-to-product variation or aging deterioration, and the RSSI value of the RF data from the transmitter may vary. When the RSSI values are compared, they always have the same magnitude relationship. Is not limited. In such a case, there is a concern that the wheel position is erroneously determined. In addition, even if the received intensity is measured cumulatively as in the method described in Patent Document 3 or the RSSI value distribution is viewed as in the method described in Patent Document 4, the same problem as described above. There is also a problem that it takes time to detect the wheel position because the RSSI value must be accumulated.

  Furthermore, in the method described in the cited document 5, since a trigger machine is required for specifying the wheel position, the problem that the cost increases due to an increase in the number of parts is inevitable. For this reason, it is desirable to be able to specify the wheel position regardless of the reception intensity and the number of receptions and without using a trigger machine.

  In view of the above points, the present invention provides a wheel position detection device that does not require the use of a trigger machine and that can accurately specify the wheel position in a shorter time and a tire air pressure detection device including the wheel position detection device. Objective.

In order to achieve the above object, in the invention according to claim 1 , in the transmitter (2) attached to each of the four wheels (5a to 5d), the transmitter (2) is connected to the wheels (5a to 5d). When the predetermined position is 0 °, the wheel (5a to 5d) is rotated once from the predetermined position and 360 ° when the wheel (5a to 5d) comes back to the predetermined position. ) To detect the position at which the transmitter (2) is located and during the period from the 0 ° position to the 180 ° position and from the 180 ° position to the 360 ° position. In the receiver (3), the transmitter (2) is 180 degrees from the 0 ° position of the RSSI value of the frame received by the receiving antenna (31) for one rotation of the tire. RSSI of the frame up to the position of ° Based on the magnitude relationship between the average value and the average RSSI value of the frame from the 180 ° position to the 360 ° position, the transmitter (2) that transmitted the frame has four wheels each. It is characterized by specifying which of (5a to 5d) is attached.

It can also be performed wheel position detection based on the difference between the maximum value and the minimum value of the RSSI value of the frame received by the receiving antenna (31) in the tire one rotation, as described in claim 1, the receiving antenna Of the RSSI values of the frame received at (31), the average value of the RSSI values of the frame from the position of 0 ° to the position of 180 ° and the position of 360 ° from the position of 180 ° are transmitted. The wheel position can be detected based on the magnitude relationship of the difference from the average value of the RSSI values of the frames up to the time .
According to such a wheel position detection device, it is assumed that the transmission output level of the transmitter (2) varies due to product-to-product variation or aging deterioration, and the RSSI value of the transmission frame from the transmitter (2) varies. However, the wheel position can be accurately detected. And since it is not necessary to receive and accumulate | store a some flame | frame like the method of patent documents 2-4, the time concerning wheel position detection can be shortened. Further, unlike the method described in Patent Document 5, no additional device such as a trigger machine is required to detect the wheel position, so that the number of parts can be reduced and the cost can be reduced. Become.

Specifically, in the first aspect of the invention , the transmitter (2) transmits a special frame as a frame when the transmitter (2) is at a position of 0 °, and is followed by a normal frame. Is transmitted, a special frame is transmitted even when the position is 180 °, and then a normal frame is additionally transmitted. When the position is again 0 °, a special frame is transmitted and frame transmission is terminated. Like that. In this way, on the receiver (3) side, the average value of the RSSI value of the frame from the position of 0 ° to the position of 180 ° and the position of 360 ° from the position of 180 ° on the transmitter (2) side. The average value of the RSSI values of the frames up to the time of can be calculated.

The invention according to claim 2 is characterized in that the receiving antenna (31) is arranged in the wheel house.

  Thus, when the receiving antenna (31) is disposed in the wheel house, the distance to the transmitter (2) disposed at a position far from the receiving antenna (31) can be further increased. For this reason, the longer the distance, the more affected by the multipath, the difference between the maximum value and the minimum value of the RSSI value, A difference between the average value and the average value of the RSSI values of the frames from the position of 180 ° to the position of 360 ° can be made large.

The frame transmission may be performed when the wheels (5a to 5d) are rotating. For example, as described in claim 3 , the transmission start condition is that the vehicle speed has reached a predetermined speed. A frame can be transmitted.

In this case, as described in claim 4, it is preferable that the first control unit (23) of the transmitter (2) is configured to perform frame transmission with a random delay after the vehicle speed reaches a predetermined speed. In this way, frame transmission can be performed at different timings, and it is possible to prevent reception on the receiver (3) side due to radio wave interference from a plurality of transmitters (2).

In the first to fourth aspects described above, the case where the present invention is grasped as the wheel position detecting device has been described. However, as shown in the fifth aspect , the wheel position detecting device can be incorporated in the tire pressure detecting device. It is. That is, the transmitter (2) includes a sensing unit (21) that outputs a detection signal corresponding to the tire air pressure provided on each of the four wheels (5a to 5d), and is sensed by the first control unit (23). The tire pressure information obtained by processing the detection signal of the unit (21) is stored in a frame and transmitted to the receiver (3). In the receiver (3), the second control unit (33) From the information related to the tire pressure, it is possible to detect the pressure of the tires provided on each of the four wheels (5a to 5d).

  In addition, the code | symbol in the bracket | parenthesis of each said means shows an example of a corresponding relationship with the specific means as described in embodiment mentioned later.

1 is a diagram illustrating an overall configuration of a tire air pressure detection device to which a wheel position detection device according to a first embodiment of the present invention is applied. 2 is a block diagram showing a transmitter 2 and a receiver 3. FIG. It is the schematic diagram which showed the relationship between the output waveform of the acceleration sensor 22, and the flame | frame transmitted. (A), (b) is the graph which showed the measurement data of the received voltage (= RSSI value) when the rotation angle of wheel 5a-5d and the transmission frame from each transmitter 2 were received with the receiving antenna 31, and its It is the chart which showed the maximum value, the minimum value, and those differences. (A), (b) are the graph and wheel which showed the measured data of the received voltage (= RSSI value) when the rotation angle of wheel 5a-5d and the transmission frame from each transmitter 2 were received with the receiving antenna 31. It is the graph which showed the average value of RSSI value when 5a-5d is 0 degrees-180 degrees, the average value of RSSI value when 180 degrees-360 degrees, and those differences.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals in the drawings.

(First embodiment)
A first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating an overall configuration of a tire air pressure detection device to which a wheel position detection device according to a first embodiment of the present invention is applied. The left direction in FIG. 1 corresponds to the front of the vehicle 1, and the right direction in FIG. 1 corresponds to the rear of the vehicle 1. With reference to this figure, the tire pressure detecting device in the present embodiment will be described.

  As shown in FIG. 1, the tire air pressure detection device is attached to a vehicle 1 and includes a transmitter 2, a receiver 3, and a display 4.

  As shown in FIG. 1, the transmitter 2 is attached to each wheel 5 a to 5 d in the vehicle 1, and detects the air pressure of the tire attached to the wheels 5 a to 5 d and relates to the tire air pressure indicating the detection result. Information is stored in a frame and transmitted. The receiver 3 is attached to the vehicle body 6 side of the vehicle 1 and receives a frame transmitted from the transmitter 2 and performs various processes and calculations based on the detection signal stored therein. Wheel position detection and tire pressure detection. The transmitter 2 creates a frame by FSK (frequency shift keying), and the receiver 3 demodulates the frame to read the data in the frame, and detects the wheel position and the tire air pressure. FIG. 2 shows a block configuration of the transmitter 2 and the receiver 3.

  As shown in FIG. 2A, the transmitter 2 includes a sensing unit 21, an acceleration sensor 22, a microcomputer 23, a transmission circuit 24, and a transmission antenna 25, and supplies power from a battery (not shown). Each part is driven based on the above.

  The sensing unit 21 includes, for example, a diaphragm type pressure sensor 21a and a temperature sensor 21b, and outputs a detection signal corresponding to the tire pressure and a detection signal corresponding to the temperature. The acceleration sensor 22 is used to detect the rotation of the wheels 5a to 5d to which the transmitter 2 is attached and to detect the vehicle speed. The acceleration sensor 22 according to the present embodiment outputs, for example, detection signals corresponding to accelerations in both directions perpendicular to the circumferential direction of the wheels 5a to 5d among accelerations acting on the wheels 5a to 5d when the wheels 5a to 5d rotate. .

  The microcomputer 23 is a well-known one having a control unit (first control unit) and the like, and executes predetermined processing according to a program stored in a memory in the control unit. Individual ID information including identification information unique to the transmitter for identifying each transmitter 2 and identification information unique to the vehicle for identifying the host vehicle is stored in the memory in the control unit.

  The microcomputer 23 receives the detection signal related to the tire pressure from the sensing unit 21, processes the signal and processes it as necessary, and stores the information related to the tire pressure in the frame together with the ID information of each transmitter 2. . Moreover, the microcomputer 23 monitors the detection signal of the acceleration sensor 22, detects the rotation of the wheels 5a to 5d to which the transmitters 2 are attached, and detects the vehicle speed. When the microcomputer 23 creates a frame, the microcomputer 23 performs frame transmission (data transmission) from the transmission antenna 25 to the receiver 3 via the transmission circuit 24 based on the rotation detection result and the vehicle speed detection result.

  Specifically, the microcomputer 23 performs frame transmission on the condition that the vehicle speed becomes a predetermined speed (for example, 10 km / h) or more and starts transmission, and the tire rotates once when the wheel position is detected. The transmission time is adjusted so as to be longer than the length of time required for the above. For example, the microcomputer 23 adjusts the transmission time of frame transmission based on the output waveform of the acceleration sensor 22.

  FIG. 3 is a schematic diagram showing the relationship between the output waveform of the acceleration sensor 22 and the transmitted frame. How the angle of the transmitter 2 changes while the wheels 5a to 5d are rotating as shown in FIG. 3 with 0 ° when the transmitter 2 is positioned below the wheels 5a to 5d. Can be confirmed from the output waveform of the acceleration sensor 22. For this reason, on the basis of this output waveform, a special frame is transmitted when the transmitter 2 is at the 0 ° position, and a normal frame is additionally transmitted subsequently, so that the transmitter 2 is positioned above the wheels 5a to 5d. When the 180 ° position is reached, a special frame is transmitted, and then a normal frame is additionally transmitted. When the transmitter 2 reaches the 0 ° position again, the special frame is transmitted and the frame transmission is terminated. . The special frame transmitted at the position of 0 ° includes data indicating the position of 0 ° and data indicating the start and end of frame transmission. Based on this special frame, the receiver 3 Confirms the position of 0 ° and confirms the start and end of frame transmission when performing wheel position detection. The special frame transmitted at the 180 ° position is data indicating the 180 ° position, and the receiver 3 confirms the 180 ° position based on the special frame. That is, by confirming the 0 ° position and the 180 ° position, it is possible to confirm at which angle of the wheels 5a to 5d the transmitter 2 is located. As the normal frame, a frame storing data related to the tire pressure is used, but it may be simple dummy data.

  As described above, the microcomputer 23 performs frame transmission at a transmission time longer than the time required for the tire to make one rotation when the wheel position is detected. Since this frame transmission is performed while monitoring one rotation of the tire while the wheels 5a to 5d are rotating, the microcomputer 23 detects the rotation by using the detection signal of the acceleration sensor 22. . That is, since the rotation of each of the wheels 5a to 5d appears in the output waveform of the detection signal of the acceleration sensor 22, the microcomputer 23 determines that the transmitter 2 is located at a predetermined position of the wheels 5a to 5d from the output waveform of the acceleration sensor 22 (this embodiment). In this case, the transmitter 2 is set to 0 ° when it is positioned at the lower position), and 360 ° when the wheels 5a to 5d are rotated once from the predetermined position and come again to the predetermined position. Rotation detection is performed to determine which angle is located. In addition, since the frame transmission start timing is set when the vehicle speed reaches a predetermined speed, the microcomputer 23 detects the vehicle speed using the detection signal of the acceleration sensor 22. That is, the output of the acceleration sensor 22 includes acceleration based on centrifugal force (centrifugal acceleration). The vehicle speed can be calculated by integrating the centrifugal acceleration and multiplying the coefficient. For this reason, the microcomputer 23 calculates the centrifugal acceleration by removing the gravitational acceleration component from the output of the acceleration sensor 22, and calculates the vehicle speed based on the centrifugal acceleration.

  The start timing of frame transmission from each transmitter 2 may be the same as the vehicle speed reaches a predetermined speed, but cannot be received on the receiver 3 side due to radio wave interference from a plurality of transmitters 2. In order to prevent this, it is preferable to set different timings by providing a random delay for each transmitter 2.

  Each transmitter 2 has a function of outputting a plurality of transmission output levels, and performs frame transmission with an appropriate transmission output level set. For example, in the handling of radio waves, the average power that can be output per unit time is determined by laws and regulations. For example, in US law standard, it is defined as 75.6 dBuV / m @ 3 m at 315 MHz, and this is the average power that can be output in 100 ms, so it is necessary to change the transmission output level according to the transmission time. For example, when the tire size is 205 / 65R15, the outer circumference is 2.034 m, so when the vehicle speed is 10 km / h (= 2.78 m / s), the time required for one rotation of the tire is 0.73 s. Become. If the frame transmission is performed in a short time, the transmission output level can be set high. However, if the frame transmission is performed during the period in which the tire rotates once, it is necessary to set the transmission output level low. For this reason, the microcomputer 23 has a function capable of adjusting the transmission output level of frame transmission in a plurality of stages, and transmits it so as to satisfy the condition of the average power that can be output per unit time determined as described above. The output level is adjusted.

  Furthermore, the microcomputer 23 performs normal frame transmission in the second and subsequent frame transmissions after the completion of the first frame transmission for wheel position detection. That is, a frame in which information related to tire air pressure is stored together with the ID information of each transmitter 2 is transmitted in a shorter transmission time (for example, 10 ms) than a single rotation of the tire.

  The transmission circuit 24 functions as an output unit that transmits a frame transmitted from the microcomputer 23 to the receiver 3 through the transmission antenna 25. For frame transmission, for example, radio waves in the RF band are used.

  The transmitter 2 configured in this way is attached to an air injection valve in each of the wheels 5a to 5d, for example, and is arranged so that the sensing unit 21 is exposed inside the tire. Thereby, the corresponding tire pressure is detected, and as described above, when the vehicle speed exceeds the predetermined speed, the frame transmission for detecting the wheel position is performed through the transmission antenna 25 provided in each transmitter 2. Thereafter, the transmitter 2 periodically transmits a signal related to tire air pressure to the receiver 3 side by performing frame transmission at regular intervals (for example, every minute). At this time, for example, by providing a random delay for each transmitter 2, the transmission timing of each transmitter 2 is shifted.

  As shown in FIG. 2B, the receiver 3 includes a receiving antenna 31, a receiving circuit 32, a microcomputer 33, and the like.

  The receiving antenna 31 is for receiving a frame transmitted from each transmitter 2. The receiving antenna 31 is fixed to the vehicle body 6 and is disposed in a place at a different distance from the wheels 5a to 5d on the front side or the rear side of the vehicle 1, more specifically in the wheel house of the left front wheel 5b. 3 is an external antenna in which the wiring is extended from the main body. Here, it is assumed that the main body of the receiver 3 is arranged in the vehicle interior, but the main body of the receiver 3 is arranged at a different distance from the wheels 5a to 5d on the front side or the rear side of the vehicle 1. You may do it. In that case, the receiving antenna 31 may not be an external antenna but may be constituted by an internal antenna built in the main body of the receiver 3.

  The receiving circuit 32 functions as an input unit that receives a transmission frame from each transmitter 2 received by the receiving antenna 31 and sends the frame to the microcomputer 33. The receiving circuit 32 measures the RSSI value of the signal (frame) received through the receiving antenna 31 and transmits the measurement result to the microcomputer 33. Specifically, the reception circuit 32 includes a detection circuit, and the reception circuit 32 corresponds to the reception level (signal strength) when the reception antenna 31 receives a frame by setting the gain of the detection circuit. Output the RSSI value.

  The microcomputer 33 corresponds to a second control unit, and executes wheel position detection processing according to a program stored in a memory in the microcomputer 33. Specifically, the microcomputer 33 measures each RSSI value input from the receiving circuit 32 when receiving a transmission frame from each transmitter 2, and the maximum value and minimum value of each RSSI value in one rotation of the tire. A value is calculated, and the difference between the maximum value and the minimum value of each RSSI value is calculated. Then, the microcomputer 33 performs wheel position detection that identifies which wheel 5a to 5d each transmitter 2 is attached to based on the difference between the maximum value and the minimum value of the RSSI values.

  In general, since the radio wave has a characteristic of being attenuated as the distance from the output source increases, if the transmission output level of each transmitter 2 is equal, the RSSI depends on the distance from each transmitter 2 to the receiving antenna 31. The value will be determined. However, since the transmission output level of each transmitter 2 varies due to manufacturing variations of the transmitter 2 and aging, the RSSI value does not necessarily depend on the distance from each transmitter 2 to the receiving antenna 31. However, since the maximum value and the minimum value of the RSSI value when the transmission frame of each transmitter 2 is received by the receiving antenna 31 are both changed due to manufacturing variations and aging deterioration, these differences are The change is canceled and becomes almost equal regardless of the transmission output level. For this reason, the microcomputer 33 stores the magnitude relationship between the difference between the maximum value and the minimum value of the RSSI value of each transmitter 2, and the maximum value and the minimum value of the RSSI value of the frame transmitted from each transmitter 2. When the difference is calculated, the wheel 5a to 5d to which each transmitter 2 is attached is specified based on the magnitude relationship between the difference between the maximum value and the minimum value of the RSSI value.

  Further, the microcomputer 33 stores the ID information of each transmitter 2 and the position of each wheel 5a to 5d to which each transmitter 2 is attached in association with the result of wheel position detection. After that, based on the ID information and tire pressure data stored in the transmission frame from each transmitter 2, the tire pressure of each wheel 5a to 5d is detected, and an electrical signal corresponding to the tire pressure is displayed. 4 is output. For example, the microcomputer 33 detects a decrease in tire air pressure by comparing the tire air pressure with a predetermined threshold Th, and outputs a signal to that effect to the display 4 when a decrease in tire air pressure is detected. Thereby, the indicator 4 is informed that the tire pressure of any of the four wheels 5a to 5d has decreased.

  The display device 4 functions as an alarm unit, and as shown in FIG. 1, is arranged at a place where the driver can visually recognize, and is configured by, for example, a meter display or the like installed in an instrument panel in the vehicle 1. The For example, when a signal indicating that the tire air pressure has decreased is sent from the microcomputer 33 in the receiver 3, the display device 4 notifies the driver of the decrease in tire air pressure by displaying that effect.

  Next, the operation of the tire pressure detection device of the present embodiment will be described. Hereinafter, the operation of the tire air pressure detection device will be described, but the description will be divided into wheel position detection and tire air pressure detection performed by the tire air pressure detection device.

  First, wheel position detection will be described. On the transmitter 2 side, rotation detection and vehicle speed detection are performed by monitoring the detection signal of the acceleration sensor 22 for each predetermined sampling period based on the power supply from the battery. Further, information related to tire air pressure such as tire air pressure and temperature is acquired based on the detection signal of the sensing unit 21, and this information is stored in the frame together with the ID information of each transmitter 2.

  When the vehicle speed becomes equal to or higher than a predetermined vehicle speed (for example, 10 km / h) based on the vehicle speed detection result, each transmitter 2 performs frame transmission from the transmission antenna 25 to the receiver 3 via the transmission circuit 24.

  Specifically, frame transmission is performed based on the rotation detection result based on the detection signal of the acceleration sensor 22. That is, the rotation of each wheel 5a to 5d appears in the output waveform of the detection signal of the acceleration sensor 22. For this reason, the microcomputer 23 of each transmitter 2 has a 0 ° position where the transmitter 2 is located at a predetermined position (a lower position in the present embodiment) of the wheels 5a to 5d from the output waveform of the acceleration sensor 22. A special frame is transmitted from time to time, followed by additional transmission of a normal frame, and when the transmitter 2 reaches a position 180 ° above the wheels 5a to 5d, the special frame is transmitted and then the normal frame is transmitted. Additional transmission is performed, and when the transmitter 2 reaches the 0 ° position again, a special frame is transmitted and frame transmission is terminated. Thus, it takes a transmission time including the period from the position of 0 ° to the position of 180 ° and the time from the position of 180 ° to the position of 360 °, that is, the wheels 5a to 5d make one rotation. Frame transmission is performed with a transmission time longer than the length of time.

  On the other hand, when frame transmission is performed from each transmitter 2, the receiver 3 receives the frame transmitted from each transmitter 2 by the reception antenna 31. This is input to the receiving circuit 32, and the RSSI value of the received signal (frame) is measured and transmitted to the microcomputer 33. Based on this, the microcomputer 33 measures each RSSI value input from the receiving circuit 32, calculates the maximum value and the minimum value of each RSSI value for one rotation of the tire, and difference between the maximum value and the minimum value. Is calculated. Then, based on the difference between the maximum value and the minimum value of the RSSI value, wheel position detection is performed to identify which wheel 5a to 5d each transmitter 2 is attached to.

  4 (a) and 4 (b) show measured data of the received voltage (= RSSI value) when the receiving antenna 31 receives the rotation angle of the wheels 5a to 5d and the transmission frame from each transmitter 2, respectively. 3 is a chart showing the graphs and their maximum and minimum values and their differences.

  As shown to Fig.4 (a), in measurement data, the RSSI value of the transmission frame of each transmitter 2 is fluctuate | varied with rotation of the wheels 5a-5d. Moreover, as shown in FIG.4 (b), the maximum value and minimum value of an RSSI value become different values for every wheel 5a-5d, and the difference of these maximum values and minimum values also differs for every wheel 5a-5d. It becomes. When the receiving antenna 31 is arranged as in the present embodiment, the order in which the difference between the maximum value and the minimum value of the RSSI value of the transmission frame of the transmitter 2 attached to each wheel 5a to 5d is small is the receiving antenna 31. In this order, the left front wheel 5b, the right front wheel 5a, the left rear wheel 5d, and the right rear wheel 5c.

  At this time, since the transmission output level of each transmitter 2 varies due to manufacturing variations or aging of the transmitter 2, the RSSI value does not necessarily depend on the distance from each transmitter 2 to the receiving antenna 31. For this reason, the maximum value and the minimum value of the RSSI value can be different values even in the transmitters 2 attached to the same wheel according to variations in the transmission output level. However, the difference between the maximum value and the minimum value of each RSSI value is almost equal regardless of the magnitude of the transmission output level. For this reason, the microcomputer 33 stores the magnitude relationship between the maximum and minimum values of the RSSI values stored in each transmitter 2, that is, in the order of the difference between the maximum and minimum values of the RSSI values. Based on this, it is possible to specify which wheel 5a to 5d each transmitter 2 is attached to.

  In this way, it is specified which of the wheels 5a to 5d each frame is attached to. Then, the microcomputer 33 stores the ID information of each transmitter 2 that has transmitted the frame in association with the position of the wheel to which it is attached.

  When wheel position detection is performed in this manner, frames are transmitted from each transmitter 2 at regular intervals thereafter, and every time a frame is transmitted from each transmitter 2, frames for four wheels are received by the receiver. 3 is received. At this time, frame transmission is performed by returning to a relatively early transmission time. Based on the ID information stored in each frame, the transmitter 2 attached to the wheels 5a to 5d is identified as the frame sent from the frame, and the information on the tire pressure is used to determine the wheels 5a to 5d. It becomes possible to detect the tire pressure.

  As described above, the receiving antenna 31 is arranged at a different location from each transmitter 2, and the maximum and minimum RSSI values when the transmission frame from each transmitter 2 is received by the receiving antenna 31 are obtained. ing. And the difference of the maximum value of each RSSI value and the minimum value is calculated | required, and wheel position detection is performed based on the magnitude relationship of the difference of the maximum value of RSSI value in each transmitter 2, and a minimum value.

  According to such a wheel position detection device, even if the transmission output level of the transmitter 2 varies due to product-to-product variation or aging deterioration, and the RSSI value of the transmission frame from the transmitter 2 varies, Wheel position detection can be performed. And since it is not necessary to receive and accumulate | store a some flame | frame like the method of patent documents 2-4, the time concerning wheel position detection can be shortened. Further, unlike the method described in Patent Document 5, no additional device such as a trigger machine is required to detect the wheel position, so that the number of parts can be reduced and the cost can be reduced. Become.

  In addition, since the frame transmission condition is that the vehicle speed is equal to or higher than the predetermined speed, or the rotation of the wheels 5a to 5d is detected using the acceleration sensor 22, the wheel position is detected only after the vehicle 1 starts to travel. The wheel position can be detected immediately after traveling.

(Second Embodiment)
A second embodiment of the present invention will be described. In the present embodiment, the RSSI value used for wheel position detection is changed with respect to the first embodiment, and the others are the same as those in the first embodiment, and therefore only different parts will be described.

  In the first embodiment, the wheel position detection is performed based on the difference between the maximum value and the minimum value of the RSSI value. In this embodiment, the RSSI value when the wheels 5a to 5d are 0 ° to 180 °. The wheel position is detected based on the difference between the average value and the average value of the RSSI values at 180 ° to 360 ° (hereinafter referred to as an average value difference in different angle ranges). As described in the first embodiment, the difference between the maximum value and the minimum value of the RSSI value is less affected by product-to-product variation of the transmitter 2 and aging deterioration, but the average value difference in different angle ranges is also affected. The same can be said.

  FIGS. 5A and 5B are graphs showing measured data of the received voltage (= RSSI value) when the receiving antenna 31 receives the rotation angle of the wheels 5a to 5d and the transmission frame from each transmitter 2. FIG. And wheels 5a to 5d are charts showing average values of RSSI values when they are 0 ° to 180 °, average values of RSSI values when wheels are 5 ° to 180 °, and their differences.

  As shown in FIG. 5A, the average RSSI value when the wheels 5a to 5d are 0 ° to 180 ° and the average RSSI value when the wheels 5a to 5 ° are 180 ° to 360 ° are different for each of the wheels 5a to 5d. As shown in FIG. 5B, the average value difference in different angle ranges is also different for each of the wheels 5a to 5d. And when the receiving antenna 31 is arranged as shown in FIG. 1, the average value difference in the different angular ranges of the RSSI values of the transmission frames of the transmitters 2 attached to the wheels 5a to 5d is, for example, in descending order. A left rear wheel 5d, a left front wheel 5b, a right front wheel 5a, and a right rear wheel 5c.

  As described above, the average value difference between the RSSI values in different angle ranges is the same as the difference between the maximum value and the minimum value of each RSSI value, and is almost equal regardless of the transmission output level. . For this reason, if the magnitude relationship of the average value difference in the angle range from which the RSSI value of each transmitter 2 differs is memorize | stored in the microcomputer 35, based on the memorized magnitude relationship, each transmitter 2 will be which wheel. It can be specified whether it is attached to 5a-5d.

  Here, the case where the left rear wheel 5d, the left front wheel 5b, the right front wheel 5a, and the right rear wheel 5c are arranged in the descending order of the average value difference in the different angle ranges of the RSSI values has been described as an example. However, this order is a value that changes depending on the vehicle type, and the magnitude relationship exemplified here may be reversed, so it is set for each vehicle type.

(Other embodiments)
(1) In each of the above embodiments, the inside of the wheel house has been described as an example of the arrangement location of the receiving antenna 31. This is because, when the receiving antenna 31 is arranged in the wheel house, the distance to the transmitter 2 arranged far from the receiving antenna 31 can be further increased. This is because the difference between the maximum value and the minimum value of the RSSI values and the average value difference in different angle ranges of the RSSI values appear greatly. However, this arrangement location is merely an example, and it is only necessary that the reception antenna 31 is arranged at a different distance from each of the wheels 5a to 5d.

  (2) In the above embodiment, as an example of adjusting the frame transmission time so as to be equal to or longer than the time required for one rotation of the tire, the rotation detection of the tire from the output waveform of the acceleration sensor 22 is performed. Frame transmission is performed with a frame length corresponding to one rotation of the tire. However, this is also merely an example, and frame transmission may be performed for a certain period of time that is equal to or longer than the length of time required for one rotation of the tire. Although the time required for one rotation of the tire varies depending on the vehicle speed, if the frame transmission is performed when the vehicle speed reaches a predetermined speed, the time required for one rotation of the tire is inevitably determined. For this reason, the frame transmission time may be set longer than the time required for one rotation of the tire at the vehicle speed.

  (3) In the first and second embodiments, based on the difference between the maximum and minimum RSSI values of frames transmitted from each transmitter 2 for one rotation of the tire and the average value difference in different angle ranges. Wheel position detection was performed. However, the wheel position may be detected based on the difference between the maximum value, minimum value, median value, or specific angle value of the RSSI values of the frames transmitted from each transmitter 2 for one rotation of the tire.

  (4) In the above embodiment, each transmitter 2 is attached to any of the four wheels 5a to 5d based on the difference between the maximum value and the minimum value of the RSSI value of the frame transmitted from each transmitter 2. The transmitter 2 is identified. However, by this method, the transmitter 2 that has transmitted the frame is specified as the transmitter 2 attached to either the front wheels 5a, 5b or the rear wheels 5c, 5d, and the right wheels 5a, 5c and the left wheels The identification of which of the wheels 5b and 5d the transmitter 2 is attached to may be performed by other methods.

  For example, the first receiving antenna is disposed at a different position from the front of the vehicle 1 and from the front wheels 5a and 5b, and the second receiving antenna is disposed at a different position from the rear of the vehicle 1 and from the rear wheels 5c and 5d. The transmitter 2 that has transmitted the frame based on the RSSI value of the frame received by each of the first and second receiving antennas is attached to either of the front wheels 5a, 5b and the rear wheels 5c, 5d. 2 is specified.

  Furthermore, by providing a wheel rotation direction detector, the rotation direction of the wheel to which the transmitter 2 is attached is detected, and data relating to this rotation direction is stored in the transmission frame of the transmitter 2. In this way, it becomes possible for the microcomputer 35 to identify the transmitter 2 attached to either the right wheels 5a, 5c or the left wheels 5b, 5d based on the rotation direction information. As such a wheel rotation direction detector, a biaxial acceleration sensor including two acceleration sensors can be used.

  Specifically, a two-axis acceleration sensor is configured by two acceleration sensors that detect accelerations in different directions, and the acceleration acting on the wheels 5a to 5d during rotation of the wheels 5a to 5d by one acceleration sensor is The acceleration in both directions perpendicular to the circumferential direction of each wheel 5a to 5d is detected, and the acceleration in both directions parallel to the circumferential direction of each wheel 5a to 5d is detected by the other acceleration sensor. And since the phase difference of the output waveform of these acceleration sensors becomes reverse by right wheel 5a, 5c and left wheel 5b, 5d, a wheel rotation direction is detectable by calculating | requiring this phase difference.

  Similarly, it is specified whether the transmitter 2 is the transmitter 2 attached to the right wheels 5a, 5c or the left wheels 5b, 5d, and is attached to either the front wheels 5a, 5b or both the rear wheels 5c, 5d. The identification of the transmitted transmitter 2 may be performed by another method.

DESCRIPTION OF SYMBOLS 1 Vehicle 2 Transmitter 3 Receiver 4 Indicator 5 (5a-5d) Wheel 6 Car body 21 Sensing part 22 Acceleration sensor 23 Microcomputer 24 Transmission circuit 25 Transmission antenna 31 Reception antenna 32 Reception circuit 33 Microcomputer

Claims (5)

Applied to a vehicle (1) to which four wheels (5a-5d) with tires are attached to the vehicle body (6);
A transmitter (2) provided on each of the four wheels (5a to 5d) and having a first control unit (23) that creates and transmits a frame including unique identification information;
A frame transmitted from the transmitter (2) is received via one receiving antenna (31) provided on the vehicle body (6) side and disposed at different distances from the four wheels (5a to 5d). A receiving circuit (32) for measuring the RSSI value of the frame received by the receiving antenna (31), and the transmitter that has transmitted the frame based on the RSSI value measured by the receiving circuit (32). (2) specifies which of the four wheels (5a to 5d) is attached to each of the four wheels (5a to 5d) and the four wheels (5a to 5d). A receiver (3) having a second control unit (33) for detecting a wheel position for storing the identification information of the transmitter (2) in association with each other,
The transmitter (2) attached to each of the four wheels (5a to 5d) is set to 0 ° when the transmitter (2) is at a predetermined position of the wheels (5a to 5d), and from the predetermined position. Rotation detection is performed to detect the position of the transmitter (2) on the wheels (5a to 5d) by setting 360 ° when the wheel (5a to 5d) rotates once and comes to the predetermined position again. Performing the transmission of the frame in a transmission time including the period from the position of 0 ° to the position of 180 ° and the period from the position of 180 ° to the position of 360 °.
The receiver (3) includes the RSSI value of the frame received by the receiving antenna (31) for one rotation of the tire until the transmitter (2) is at a position of 0 ° to a position of 180 °. The transmitter that has transmitted the frame based on the magnitude relationship of the difference between the average value of the RSSI value of the frame and the average value of the RSSI value of the frame from the position of 180 ° to the position of 360 ° ( 2) specify which of the four wheels (5a to 5d) each is attached to ,
The transmitter (2) transmits a special frame as the frame when the transmitter (2) is at a position of 0 °, and additionally transmits a normal frame following that to the position of 180 °. A wheel position detecting device characterized in that a special frame is transmitted after that, a normal frame is additionally transmitted, and the special frame is transmitted again when the vehicle reaches the 0 ° position again to end the frame transmission . The wheel position detecting device according to claim 1 , wherein the receiving antenna (31) is arranged in a wheel house. Wherein said first control section of the transmitter (2) (23), the vehicle speed is a condition for starting transmission that reaches a predetermined speed, according to claim 1 or 2, characterized in that transmitting the frame Wheel position detection device. The wheel position detection device according to claim 3 , wherein the first control unit (23) of the transmitter (2) transmits the frame with a random delay after the vehicle speed reaches a predetermined speed. . A tire pressure detecting device including the wheel position detecting device according to any one of claims 1 to 4 ,
The transmitter (2) includes a sensing unit (21) that outputs a detection signal corresponding to the air pressure of the tire provided on each of the four wheels (5a to 5d), and the first control unit (23). After storing the information on the tire pressure obtained by signal processing the detection signal of the sensing unit (21) in a frame, the frame is transmitted to the receiver (3),
In the receiver (3), the second control unit (33) detects air pressures of the tires provided to the four wheels (5a to 5d) from information on the tire air pressures. Tire pressure detection device.

Images