JP2012210911A - Wheel position detecting device and tire air pressure detecting device equipped with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately identify a wheel position.SOLUTION: An RSSI value corresponding to a reception level when a frame is received with a reception antenna is obtained, but the RSSI value is saturated without raising an output such that the RSSI value becomes larger to such a degree as the reception level rises across the entire estimated range as the reception level. With this configuration, the RSSI value of a transmission frame of a transmitter of both rear wheels close to the reception antenna is saturated to be a constant value. Since the RSSI value of the transmission frame of the transmitter of both front wheels which are away from it basically fluctuates although partially saturated, a front wheel and a rear wheel are identified depending on whether the RSSI value is constant or there exists a difference. Further, based on the rotational direction information stored in the transmission frame from the transmitters, a left wheel and a right wheel are identified. Thus, all four wheels can be identified.

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 in order to determine which of the front and rear wheels, but when the comparison result of the RSSI value is always the same. Is not limited. That is, when the RSSI values are compared, in some cases, the magnitude relationship between the RSSI values may be reversed, or the difference between the RSSI values may be reduced between the front and rear wheels. In such a case, there is a concern that the wheel position is erroneously determined. 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, some RSSI values are used. The magnitude relationship between the front and rear wheels may be reversed, and the difference in RSSI values may be smaller between the front and rear wheels.

  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 does not require the use of a trigger machine, and does not cause a problem that the magnitude relationship between RSSI values is reversed. Even if the difference in RSSI values is small between the front and rear wheels, the present invention is accurate. It is an object of the present invention to provide a wheel position detection device capable of specifying a wheel position and a tire air pressure detection device including the wheel position detection device.

  In order to achieve the above object, according to the first aspect of the present invention, at least the receiving antenna (31) of the receiver (3) is connected to both front wheels (5a, 5b) and both rear wheels (5c, 5d) when the RSSI value of the frame received by the receiving circuit (32) is measured by the receiving circuit (32) and is received by the receiving antenna (31). The RSSI value increases as the reception level increases until the reception level, which is the signal intensity of the frame, reaches a predetermined value. When the reception level exceeds the predetermined value, the RSSI value is measured as a constant value. The second control unit (33) receives the frames transmitted from the transmitters (2a to 2d) provided on the four wheels (5a to 5d) when detecting the wheel position. Whether the frame is transmitted from the transmitter (2a, 2c) attached to the right wheel (5a, 5c) or the left wheel (5b, 5d) based on the rotation direction information contained in the minute frame And a frame having a constant RSSI value based on the change of the RSSI value is the two of the front wheels (5a, 5b) and the rear wheels (5c, 5d) that are closer to the receiving antenna (31). The frame in which the RSSI value changes is determined from the receiving antenna (31) of both front wheels (5a, 5b) and both rear wheels (5c, 5d). The far two wheels 5a, 5b) by specifying that the transmitter (2a-2d) is attached to each of the four wheels (5a-5d) It is a feature.

  As described above, in the receiver (3), the RSSI value corresponding to the reception level when the frame is received by the reception antenna (31) is obtained, and the RSSI increases as the reception level increases in the entire range assumed as the reception level. The output is not increased so that the RSSI value is saturated. By doing in this way, with a rotation of a wheel (5a-5d), a wheel (5c, 5d) near a receiving antenna (31) among both front wheels (5a, 5b) and both rear wheels (5c, 5d). The RSSI value of the transmission frame of the transmitter (2c, 2d) is saturated and becomes a constant value, and the RSSI value of the transmission frame of the transmitter (2a, 2b) of the far wheel (5a, 5b) may be partially saturated. Basically there is something that can be changed. Therefore, it was transmitted from the transmitters (2a to 2d) attached to either the front wheels (5a, 5b) or the rear wheels (5c, 5d) based on whether the RSSI value is constant or different. You can specify whether it is a frame.

  Moreover, based on the rotation direction information stored in the transmission frame from each transmitter (2a-2d), the transmitter in which the frame was attached to either the right wheel (5a, 5c) or the left wheel (5b, 5d) It can be specified whether it is transmitted from (2a, 2c). Thereby, all the transmitters (2a-2d) of four wheels (5a-5d) can be specified, and which wheel (5a-5d) each transmitter (2a-2d) is attached to. The wheel position to be identified can be detected. Therefore, there is no need to use a trigger machine, and there is no problem that the magnitude relationship between RSSI values is reversed, and the wheel position can be accurately specified even if the difference in RSSI values is small between the front and rear wheels. A position detecting device can be obtained.

  For example, as described in claim 2, as the wheel rotation direction detecting means (22), the wheel (5a to 5d) is rotated when the wheel (5a to 5d) to which the transmitter (2a to 2d) is attached is rotated. A biaxial acceleration sensor having an acceleration sensor (22a) that detects acceleration in both directions perpendicular to the circumferential direction and an acceleration sensor (22b) that detects acceleration in both directions parallel to the circumferential direction can be applied.

  In the invention according to claim 3, the transmitters (2a to 2d) calculate the vehicle speed from the acceleration detected by the acceleration sensors (22a, 22b) included in the biaxial acceleration sensor, and the vehicle speed becomes a predetermined vehicle speed. It is characterized by transmitting a frame when it reaches.

  As described above, since the frame transmission is performed when the vehicle speed becomes equal to or higher than the predetermined speed, the frame transmission can be prevented from being performed when the vehicle is stopped, and the battery life can be improved. Further, it is assumed that a spare tire is mounted on the vehicle (1), and the spare tire is also provided with a transmitter. However, since the spare tire does not rotate as the vehicle (1) travels, the transmission of the frame is triggered by the fact that the vehicle speed is equal to or higher than the predetermined speed, so that the transmitter attached to the spare tire can be used. Can prevent frames from being transmitted. For this reason, even when a spare tire is equipped with a transmitter, it is possible to accurately detect the wheel position.

  Further, as in the invention described in claim 4, the second control unit (33) receives the reception antenna (31) among a plurality of different frames transmitted from the same transmitter (2a to 2d) as a change in the RSSI value. ), The RSSI values at the timing determined from the start of reception are compared, and if the RSSI values are constant, the frame is out of both front wheels (5a, 5b) and both rear wheels (5c, 5d). If it is determined that the signal is transmitted from the two wheels (5c, 5d) closer to the receiving antenna (31), and there is a difference between the RSSI values, the frame is composed of both front wheels (5a, 5b) and both rear wheels. (5c, 5d) can be identified as being transmitted from the two wheels (5a, 5b) farther from the receiving antenna (31).

  Further, as in the invention described in claim 5, the second controller (33) is configured to change the RSSI value as a maximum value of the RSSI values of a plurality of different frames transmitted from the same transmitter (2a to 2d). If the maximum values of the RSSI values are constant, the two wheels closer to the receiving antenna (31) of the front wheels (5a, 5b) and the rear wheels (5c, 5d) (5c, 5d) is specified, and if there is a difference between the maximum RSSI values, the frame is a receiving antenna of the front wheels (5a, 5b) and the rear wheels (5c, 5d). It can also be specified that the transmission is made from the two wheels (5a, 5b) far from (31).

  Similarly, as in the invention described in claim 6, the second control unit (33) sets the minimum RSSI value of a plurality of different frames transmitted from the same transmitter (2 a to 2 d) as the change of the RSSI value. If the minimum values of the RSSI values are constant values, the frame is the two of the front wheels (5a, 5b) and the rear wheels (5c, 5d) that are closer to the receiving antenna (31). If it is transmitted from one wheel (5c, 5d) and there is a difference between the minimum values of RSSI values, the frame is out of both front wheels (5a, 5b) and both rear wheels (5c, 5d). It can also be specified that the signal is transmitted from the two wheels (5a, 5b) far from the receiving antenna (31).

  Further, as in the invention described in claim 7, the second control unit (33) determines the change of the RSSI value in one frame of the frames transmitted from the transmitters (2a to 2d) as the change of the RSSI value. If the RSSI value is a constant value, the frame is from the two wheels (5c, 5d) closer to the receiving antenna (31) of the front wheels (5a, 5b) and the rear wheels (5c, 5d). If there is a change in the RSSI value, it is determined that the frame has been transmitted, and the two wheels that are far from the receiving antenna (31) of the front wheels (5a, 5b) and the rear wheels (5c, 5d) It can also be specified that it is transmitted from (5a, 5b).

  In the first to seventh aspects, the present invention is shown as the wheel position detecting device. However, as shown in the eighth aspect, the wheel position detecting device can be incorporated in the tire pressure detecting device. That is, the transmitter (2a to 2d) includes a sensing unit (21) that outputs a detection signal corresponding to the tire pressure provided on each of the four wheels (5a to 5d), and the first control unit (23). The tire pressure information obtained by signal processing of the detection signal of the sensing unit (21) is stored in a frame and transmitted to the receiver (3). In the receiver (3), the second control unit (33) Thus, it is possible to detect the air pressure of the tire provided on each of the four wheels (5a to 5d) from the information on the tire air pressure.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence 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. It is a figure which shows the block configuration of the transmitters 2a-2d and the receiver 3. FIG. It is the figure which showed an example of the frame structure. An example of a mounting form of each wheel 5a to 5d of the wheel rotation direction detection unit 22 provided in the transmitter 2 and an output waveform of acceleration detected by each of the acceleration sensors 22a and 22b in the mounting form are shown. It is a figure. It is the graph which showed the relationship between a reception level and an RSSI value. It is the figure which showed the relationship between the rotation angle of the wheels 5a-5d, the measurement data of signal strength when transmitting a frame from each transmitter 2a-2d, and RSSI value. (A) is a flowchart showing processing performed by the microcomputer 23 of the transmitters 2a to 2d, and (b) is a flowchart showing processing performed by the microcomputer 33 of the receiver 3. It is a figure which shows the whole structure of the tire-pressure detection apparatus with which the wheel position detection apparatus demonstrated by other embodiment is applied.

  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 (2a to 2d), a receiver 3, and a display 4.

  As shown in FIG. 1, the transmitters 2 a to 2 d are attached to the wheels 5 a to 5 d in the vehicle 1. The tires detect the air pressure of the tires attached to the wheels 5 a to 5 d and indicate the detection results. Information on air pressure is stored in a frame and transmitted by RF. The receiver 3 is attached to the vehicle body 6 side of the vehicle 1, and receives RF frames transmitted from the transmitters 2a to 2d and performs various processes and computations based on detection signals stored therein. Etc. to detect the wheel position and the tire air pressure. FIG. 2 shows a block configuration of the transmitters 2 a to 2 d and the receiver 3.

  As shown in FIG. 2 (a), the transmitter 2 (2a to 2d) includes a sensing unit 21, a wheel rotation direction detection unit 22, a microcomputer 23, a transmission antenna 24, and a battery 25. Each unit is driven based on power supply from the battery 25.

  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 wheel rotation direction detection unit 22 detects whether the transmitter 2 is attached to the right wheel group 5a, 5c or the left wheel group 5b, 5d whose wheel rotation directions are opposite to each other. This corresponds to the wheel rotation direction detection means of the invention. The wheel rotation direction detection unit 22 is provided with a biaxial acceleration sensor including two acceleration sensors 22a and 22b (see FIG. 4). The functions of the acceleration sensors 22a and 22b will be described later.

  The microcomputer 23 is a well-known device including a control unit (first control unit), a transmission unit, and the like, and executes predetermined processing according to a program stored in a memory in the control unit. In the memory in the control unit, individual ID information including identification information unique to the transmitter for identifying each of the transmitters 2a to 2d and identification information unique to the vehicle for identifying the host vehicle is stored.

  The microcomputer 23 receives the detection signal related to the tire air pressure from the sensing unit 21, processes the signal and processes it as necessary, and stores the information regarding the tire air pressure in the frame together with the ID information of each of the transmitters 2a to 2d. Store. Further, the microcomputer 23 monitors the detection signals of the acceleration sensors 22a and 22b during a certain period, and detects the rotation direction of the wheels 5a to 5d to which the transmitters 2a to 2d are attached. In the microcomputer 23, data relating to the tire pressure is stored in this rotational direction, that is, the rotational direction information indicating the transmitter 2 attached to either the right wheel group 5a, 5c or the left wheel group 5b, 5d. Stored in a frame.

  FIG. 3 is a diagram illustrating an example of a frame configuration. The frame shown in this figure is a common frame used for both wheel position detection and tire air pressure detection. As shown in this figure, the frame starts with a synchronization code indicating the start of transmission, individual ID information given to each transmitter 2, rotational direction information, tire pressure information (air pressure and temperature), battery voltage, etc. Error detection information indicating that an error has been detected is stored in the information and data transmitted by the transmitter itself. Of these, the rotation direction information is used to detect whether the transmitters 2a to 2d are attached to the right wheel group 5a, 5c or the left wheel group 5b, 5d, and the tire pressure information is used for each wheel. Used to detect tire pressures 5a-5d.

  When the microcomputer 23 creates a frame, the microcomputer 23 transmits the frame from the transmission antenna 24 to the receiver 3 via the transmission unit with the same signal strength (electric field strength of radio waves). The process of transmitting this frame toward the receiver 3 is also performed according to the above program. In the present embodiment, the microcomputer 23 obtains the vehicle speed, and when the vehicle speed reaches a predetermined speed (for example, 30 km / h) as a trigger, frame transmission to the receiver 3 is started. Frame transmission is repeatedly performed at regular intervals until the transmission end speed is reached (for example, less than 30 km / h).

  The transmitters 2a to 2d configured as described above are attached to air injection valves in the wheels of the wheels 5a to 5d, for example, and are arranged so that the sensing unit 21 is exposed to the inside of the tire. Thus, the corresponding tire pressure is detected, and as described above, when the vehicle speed exceeds a predetermined speed, frames are transmitted at regular intervals (for example, every minute) through the transmission antenna 24 provided in each of the transmitters 2a to 2d. By transmitting, a signal related to the tire pressure is periodically transmitted to the receiver 3 side.

  Next, the wheel rotation direction detection unit 22 provided in each transmitter 2 will be described with reference to FIG. FIG. 4 shows an example of a mounting form of each wheel 5a to 5d of the wheel rotation direction detection unit 22 provided in the transmitter 2, and the acceleration detected by each acceleration sensor 22a, 22b when the mounting form is adopted. It is the figure which showed the output waveform.

  As shown in this figure, the wheel rotation direction detection unit 22 is configured by a biaxial acceleration sensor including acceleration sensors 22a and 22b that detect accelerations in different directions. One acceleration sensor 22a can detect acceleration in both directions perpendicular to the circumferential direction of the wheels 5a to 5d among the accelerations acting on the wheels 5a to 5d when the wheels 5a to 5d rotate, and the other acceleration sensor 22b It arrange | positions so that the acceleration of both directions parallel to the circumferential direction of the wheels 5a-5d can be detected.

  Therefore, the acceleration sensor 22a detects acceleration in both directions perpendicular to the circumferential direction of the wheels 5a to 5d, and generates an output corresponding to the gravitational acceleration. For this reason, when the transmitter 2 is located at the upper position of the wheels 5a to 5d, the acceleration sensor 22a outputs an output indicating the gravitational acceleration as a positive value. When the wheels 5a to 5d are rotated by 180 ° and the wheel side transceiver 2 is located at a lower position of the wheels 5a to 5d, an output indicating a gravitational acceleration as a negative value is obtained.

  On the other hand, the acceleration sensor 22b detects the acceleration in both directions parallel to the circumferential direction of the wheels 5a to 5d, and generates an output corresponding to the gravitational acceleration, like the acceleration sensor 22a. However, since the acceleration angle that the acceleration sensor 22b can detect with respect to the acceleration sensor 22a is shifted by 90 °, the phase of the output waveform corresponding to the detected gravitational acceleration is also different from the phase of the output waveform of the acceleration sensor 22a. It is shifted by 90 °. That is, in FIG. 4, when the transmitter 2 is at a position shifted by 90 ° counterclockwise with respect to the centers of the wheels 5a to 5d, an output indicating a gravitational acceleration as a negative value is obtained. When the wheels 5a to 5d are rotated by 180 ° in FIG. 4 and the transmitter 2 is positioned 90 ° clockwise relative to the centers of the wheels 5a to 5d, the output indicating the gravitational acceleration as a positive value is output. It becomes.

  Therefore, as shown in FIG. 4, when the rotation direction of the wheels 5a to 5d is counterclockwise as shown in FIG. 4, the phase of the output waveform of the acceleration sensor 22b is advanced by 90 ° with respect to the output waveform of the acceleration sensor 22a. It becomes a state. Conversely, when the rotation directions of the wheels 5a to 5d are clockwise as shown in FIG. 4, the phase of the output waveform of the acceleration sensor 22b is delayed by 90 ° with respect to the output waveform of the acceleration sensor 22a.

  Thus, when the rotation directions of the wheels 5a to 5d are reversed, the phase shift of the output waveforms of the acceleration sensors 22a and 22b is also reversed. By utilizing this fact, by including rotation direction information indicating the rotation direction of the wheels 5a to 5d in the frame transmitted from the transmitter 2 to the receiver 3, the frame is received by the receiver 3 on the right wheel groups 5a and 5c. And the left wheel group 5b, 5d can be identified from the transmitter 2 attached.

  In the above description, the centrifugal force included in the outputs of the acceleration sensors 22a and 22b is ignored, but the output of the acceleration sensors 22a and 22b includes acceleration based on the centrifugal force (centrifugal acceleration). The vehicle speed can be calculated by integrating the centrifugal acceleration and multiplying the coefficient. For this reason, the microcomputer 33 calculates the centrifugal acceleration by removing the gravitational acceleration component from the output of either of the acceleration sensors 22a and 22b, and calculates the vehicle speed based on the centrifugal acceleration.

  As shown in FIG. 2B, the receiver 3 includes a receiving antenna 31, a receiving circuit 32, a microcomputer 33, a power supply circuit 34, and an interface (I / F) circuit 35.

  The receiving antenna 31 is for receiving frames sent from the transmitters 2a to 2d. The receiving antenna 31 is fixed to the vehicle body 6 and is disposed closer to the front or rear of the vehicle 1 so that either one of the front wheels 5a, 5b and the rear wheels 5c, 5d is more than the other. The distance is made closer. In the present embodiment, the receiving antenna 31 is disposed at a location near the rear of the vehicle 1, for example, a rear bumper, and compared with the transmitters 2a and 2b attached to both front wheels 5a and 5b, both rear wheels 5c and 5d. It is arranged near the transmitters 2c and 2d attached to the transmitter.

  The reception circuit 32 functions as an input unit that receives transmission frames from the transmitters 2 a to 2 d received by the reception antenna 31 and sends the frames 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.

  However, the output is not such that the RSSI value increases as the reception level increases in the entire range of the reception level assumed when the frames transmitted from the transmitters 2a to 2d are received by the reception antenna 31. The relationship between the reception level and the RSSI value is as shown in FIG. That is, as shown in FIG. 5, until the reception level of the frame reaches a predetermined value, the RSSI value increases as the reception level increases. When the reception level exceeds the predetermined value, the RSSI value is measured as a constant value. It has become. In general, the gain of the detection circuit is set to such a value that the RSSI value also changes over the entire range of change in the reception level assumed within the voltage range that can be output by the detection circuit. On the other hand, in the case of the present embodiment, when a part of the assumed reception level change range, that is, when the reception level becomes larger than a predetermined value, it is saturated beyond the voltage range that can be output by the detection circuit, and the RSSI value The gain of the detection circuit is set so that becomes a constant value.

  As for the gain of the detection circuit at this time, the RSSI values of the transmission frames of the transmitters 2c and 2d attached to the rear wheels 5c and 5d arranged at positions close to the receiving antenna 31 are constant values, and the positions are far from each other. It is preferable that the RSSI values of the transmission frames of the transmitters 2c and 2d attached to the two front wheels 5a and 5b arranged in the vehicle are set so as to vary.

  That is, using the fact that the electric field strength of radio waves attenuates according to the distance from the radio wave generation source, the received frames of transmitters 2c and 2d have a high reception level, so the RSSI value is saturated and becomes a constant value. Since the reception levels of the transmission frames of the transmitters 2a and 2b are small, the RSSI value can be basically not saturated even if the RSSI value is partially saturated.

  FIG. 6 is a diagram showing the relationship between the rotation angle of the wheels 5a to 5d and the measured data of the signal strength and the RSSI value when a frame is transmitted from each of the transmitters 2a to 2d. As shown in FIG. 6A, in the measured data, the signal strength of the transmission frame of each of the transmitters 2a to 2d varies with the rotation of the wheels 5a to 5d. In FIG. 6A, the signal strengths of the transmission frames of the transmitters 2a and 2b attached to both front wheels 5a and 5b are attached to both rear wheels 5c and 5d throughout the entire range even if the rotation angle changes. An example is given in which the signal strength of the transmission frame of the transmitters 2c and 2d is smaller. However, depending on the situation, the magnitude relationship may be partially reversed.

  On the other hand, as shown in FIG. 6B, with respect to the RSSI value, the RSSI value of the transmission frame of the transmitters 2c and 2d is saturated and becomes a constant value as the wheels 5a to 5d rotate, and the transmitters 2a and 2b. Although the RSSI value of the transmission frame is partially saturated, it basically varies.

  In the present embodiment, using such a phenomenon, when the receiver 3 receives a frame based on the change in the RSSI value, the transmitter 2a to 2d attached to any of the wheels 5a to 5d. Specify whether it was sent more. Specifically, a frame having a constant RSSI value can be identified as being transmitted from the transmitters 2c and 2d attached to the rear wheels 5c and 5d close to the receiving antenna 31, and a frame whose RSSI value fluctuates is received. It can be specified that it is transmitted from the transmitters 2a and 2b attached to the front wheels 5a and 5b far from the antenna 31. Thereby, the wheel position is specified.

  In order to obtain such a relationship between the reception level and the RSSI value, it is only necessary to adjust the gain setting of the detection circuit, for example, as described above. There is no need to change.

  The microcomputer 33 corresponds to the second control unit, and performs transmission from each of the transmitters 2a to 2d as described above by executing wheel position detection processing according to a program stored in a memory in the microcomputer 33. Using the RSSI value of the frame, wheel position detection is performed to specify which wheel 5a to 5d each transmitter 2a to 2d is attached to. Further, the microcomputer 33 stores the ID information of the transmitters 2a to 2d in association with the positions of the wheels 5a to 5d to which the transmitters 2a to 2d are attached based on the wheel position detection result. Thereafter, based on the ID information and the tire pressure data stored in the transmission frames from the transmitters 2a to 2d, the tire pressure of each wheel 5a to 5d is detected.

  The power supply circuit 34 generates a power supply voltage for the microcomputer 33 and the receiving circuit 32 based on the battery voltage. The I / F circuit 35 plays a role of outputting the tire air pressure in the microcomputer 33 to the display 4.

  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, wheel position detection processing by a tire air pressure detection device to which the wheel position detection device configured as described above is applied will be described. FIG. 7A is a flowchart showing processing performed by the microcomputer 23 of the transmitters 2a to 2d, and FIG. 7B is a flowchart showing processing performed by the microcomputer 33 of the receiver 3.

  First, on the transmitters 2a to 2d side, the rotation direction information is obtained by monitoring the detection signal of the biaxial acceleration sensor at regular intervals (for example, 1 min) based on the power supply from the battery 25, and the sensing unit 21 Information on tire pressure such as tire pressure and temperature is acquired based on the detection signal, and a frame is created based on the information. And the process shown to Fig.7 (a) is performed. Specifically, each of the transmitters 2a to 2d determines whether or not the vehicle speed is equal to or higher than a predetermined speed (for example, 30 km / h) (step 100). Data transmission is performed to transmit a frame in which information on the information is stored (step 110). In this data transmission, it is preferable to transmit a plurality of frames continuously in order to increase the reception rate.

  As described above, the vehicle speed is calculated by calculating the centrifugal acceleration by removing the gravitational acceleration component from the output of the acceleration sensor 22a, integrating the centrifugal acceleration and multiplying the coefficient. For data transmission, for example, each transmitter 2a to 2d is set so that the timing of regular transmission is shifted randomly. In this way, frames in which the rotational direction information and information about tire pressure are stored are transmitted from the transmitters 2a to 2d.

  On the other hand, on the receiver 3 side, when an ignition switch (not shown) is turned on and the power supply circuit 34 generates the power supply voltage based on the power supply from the battery, the receiver 3 starts to operate, and is displayed at every predetermined control cycle. The process shown in 7 (b) is executed.

  First, as shown in FIG. 7B, the receiver 3 performs data reception (step 200), and determines whether two frames of data for four wheels have been acquired (step 210), 4 Wait until two cycles of ring data are received. The term “two frames” here means that different frames are received from the transmitters 2a to 2d, and two frames transmitted in adjacent cycles may be received, or different contents within the same cycle. If a plurality of frames are continuously transmitted, two of them may be received. And when the reception of the data for the four wheels is completed, that is, when all the frames transmitted from the transmitters 2a to 2d provided in the wheels 5a to 5d are received, based on the acquired data for the four wheels, The wheel position is specified (step 220).

  Specifically, since the frames transmitted from the transmitters 2a to 2d include the rotation direction information, the frame is converted into the right wheel group 5a based on the rotation direction information included in the data for the four wheels. 5c and the left wheel group 5b and 5d are identified from the transmitter 2 attached thereto. The ID information is stored separately for the transmitters 2a and 2c attached to the right wheel groups 5a and 5c and the transmitters 2b and 2d attached to the left wheel groups 5b and 5d.

  On the other hand, the RSSI value of each frame when data for four wheels is received is measured, and the frames in which the RSSI value does not change between the frames for two cycles are transmitted from the transmitters 2c and 2d of both rear wheels 5c and 5d. While specifying that it was transmitted, the frame in which the RSSI value is changing is specified as having been transmitted from the transmitters 2a and 2b of both front wheels 5a and 5b. Specifically, since the wheels 5a to 5d are rotating during frame transmission by each transmitter 2, the reception level changes even in the same frame. For this reason, in this embodiment, when a frame is received, the RSSI value is measured at a timing determined from the start of reception, and the RSSI value measured at the same timing between the frames for two periods is a constant value or there is a difference. Based on this, the above identification is performed. Each ID information is stored separately for the transmitters 2a and 2b attached to both front wheels 5a and 5b and for the transmitters 2c and 2d attached to both rear wheels 5c and 5d.

  Thereafter, in the ID information stored in the received frame, the transmitters 2a and 2c attached to the right wheel groups 5a and 5c are identified, and the transmitters 2c and 2d of both rear wheels 5c and 5d The identified item is identified as the ID information of the transmitter 2c of the right rear wheel 5c. Identify the transmitters 2a and 2c attached to the right wheel groups 5a and 5c, and identify the transmitters 2a and 2b of both front wheels 5a and 5b as the ID information of the transmitter 2a of the right front wheel 5a. To do. The ID information of the transmitter 2d of the left rear wheel 5d is specified as the transmitters 2b and 2d attached to the left wheel group 5b and 5d and specified as the transmitters 2c and 2d of both rear wheels 5c and 5d. Is identified. The ID information of the transmitter 2b of the left front wheel 5b is specified as the transmitters 2b and 2d attached to the left wheel groups 5b and 5d, and the transmitter 2a and 2b of both front wheels 5a and 5b is specified. Is identified. Thereby, it is possible to specify the transmitters 2a to 2d of all four wheels 5a to 5d, and perform wheel position detection to specify which wheel 5a to 5d each transmitter 2a to 2d is attached to. Can do.

  As described above, the receiver 3 obtains the RSSI value corresponding to the reception level when the frame is received by the reception antenna 31, and the RSSI value increases as the reception level increases in the entire range assumed as the reception level. The output is not increased and the RSSI value is saturated. That is, when a part of the assumed reception level change range, that is, when the reception level becomes larger than a predetermined value, the voltage exceeds the voltage range that can be output from the detection circuit, and the RSSI value becomes a constant value. .

  By doing so, the RSSI values of the transmission frames of the transmitters 2c and 2d of both rear wheels 5c and 5d that are close to the receiving antenna 31 with the rotation of the wheels 5a to 5d are saturated and become a constant value, and both front wheels that are far Although the RSSI values of the transmission frames of the transmitters 2a and 2b of 5a and 5b are partially saturated, they can be basically changed. Therefore, based on whether the RSSI value measured at the same timing between frames is a constant value or a difference, transmission is performed from the transmitters 2a to 2d attached to either the front wheels 5a, 5b or the rear wheels 5c, 5d. Can be identified.

  Moreover, based on the rotation direction information stored in the transmission frame from each transmitter 2a-2d, it transmits from transmitter 2a-2d attached to either of right wheel group 5a, 5c and left wheel group 5b, 5d. Can be specified.

  Thereby, it is possible to specify the transmitters 2a to 2d of all four wheels 5a to 5d, and perform wheel position detection to specify which wheel 5a to 5d each transmitter 2a to 2d is attached to. Can do.

  And if wheel position detection is performed in this way, the frame for four wheels will be received by the receiver 3 every time a frame is transmitted from each transmitter 2a-2d for every fixed period after that. Based on the ID information stored in each frame, the transmitters 2a to 2d attached to the wheels 5a to 5d are identified as frames, and the wheels 5a to 5d are determined from the tire pressure information. It becomes possible to detect the tire pressure of 5d.

  Therefore, there is no need to use a trigger machine, and there is no problem that the magnitude relationship between RSSI values is reversed, and the wheel position can be accurately specified even if the difference in RSSI values is small between the front and rear wheels. A position detection device and a tire air pressure detection device including the position detection device can be provided. Further, since the frame transmission is performed when the vehicle speed becomes equal to or higher than the predetermined speed, the frame transmission can be prevented from being performed when the vehicle is stopped, and the battery life can be improved.

  In addition, it is assumed that the vehicle 1 is equipped with a spare tire and the spare tire is also provided with the transmitter 2. However, since the spare tire does not rotate as the vehicle 1 travels, the transmission of the frame is triggered by the fact that the vehicle speed is equal to or higher than the predetermined speed, so that the transmitter 2 attached to the spare tire can be used. It is possible to prevent frame transmission. For this reason, even when the transmitter 2 is provided in the spare tire, the wheel position can be accurately detected.

(Second Embodiment)
A second embodiment of the present invention will be described. In the present embodiment, the RSSI value comparison method is changed with respect to the first embodiment, and the others are the same as those in the first embodiment. Therefore, only the parts different from the first embodiment will be described.

  In the first embodiment, when a frame is received, the RSSI value is measured at a timing determined from the start of reception, and the RSSI value measured at the same timing between frames for two periods is a constant value or there is a difference. Based on the above, it was specified whether the frame was transmitted from the transmitters 2a to 2d attached to either the front wheels 5a, 5b or the rear wheels 5c, 5d. On the other hand, in this embodiment, the comparison target of the RSSI values of the frames for two periods is not the RSSI value at the same timing, but the maximum values of the RSSI values between the frames are compared. The above identification is performed based on whether the value is constant or different.

  As described above, the RSSI value of the frame that is sent for each period also changes during frame transmission as the wheels 5a to 5d rotate. However, for the transmitters 2c and 2d attached to both rear wheels 5c and 5c close to the receiving antenna 31, the RSSI value remains constant, and the transmitter 2a attached to both front wheels 5a and 5b far from the receiving antenna 31. For 2b, the RSSI value changes. For this reason, the maximum RSSI values between the frames are compared with each other, and if they are constant values, the frame is identified as being transmitted from the transmitters 2c and 2d attached to both rear wheels 5c and 5c. If there is a difference between them, the frame can be identified as being transmitted from the transmitters 2a and 2b attached to both front wheels 5a and 5b.

  Thus, based on whether the maximum values of the RSSI values between the frames are compared with each other and the maximum values are constant or different, it is determined which of the front wheels 5a, 5b and the rear wheels 5c, 5d It is also possible to specify whether the frame is transmitted from the attached transmitters 2a to 2d. And like the said 1st Embodiment, based on the rotation direction information stored in the transmission frame from each transmitter 2a-2d, it attaches to either right wheel group 5a, 5c and left wheel group 5b, 5d. It is specified whether the frame is transmitted from the transmitters 2a to 2d.

  Thereby, it is possible to specify the transmitters 2a to 2d of all four wheels 5a to 5d, and perform wheel position detection to specify which wheel 5a to 5d each transmitter 2a to 2d is attached to. Can do.

  As can be seen from FIG. 6, the RSSI values of the frames transmitted from the transmitters 2a and 2b attached to the front wheels 5a and 5b may be partially saturated, but this is only a part. Therefore, it is highly possible that the maximum value of the RSSI value becomes a value when the RSSI value is not saturated in any one of the frames of two periods. Therefore, based on whether the maximum values are a constant value or a difference, it is determined whether the frame is transmitted from the transmitters 2a to 2d attached to the front wheels 5a and 5b or the rear wheels 5c and 5d. Can be identified. If there are three or more wheels whose maximum values for two periods are constant, frames for three periods may be confirmed.

(Third embodiment)
A third embodiment of the present invention will be described. This embodiment is also a modification of the RSSI value comparison method with respect to the first embodiment, and is otherwise the same as the first embodiment, so only the parts different from the first embodiment will be described.

  In the present embodiment, as the comparison target of the RSSI values of the frames for two periods, the minimum values of the RSSI values between the frames are compared, and the above identification is performed based on whether the minimum values are a constant value or a difference. I do. That is, as in the case where the maximum values of the RSSI values between the frames are to be compared with each other, when the minimum values are to be compared with each other, if the values are constant, the frame is placed on both rear wheels 5c and 5c. If the transmitters 2c and 2d are attached, the frames are identified as being transmitted from the transmitters 2a and 2b attached to the front wheels 5a and 5b.

  Thus, based on whether the minimum values of the RSSI values between the frames are compared with each other and the minimum values are constant or different, it is determined which of the front wheels 5a, 5b and the rear wheels 5c, 5d It is also possible to specify whether the frame is transmitted from the attached transmitters 2a to 2d. And like the said 1st Embodiment, based on the rotation direction information stored in the transmission frame from each transmitter 2a-2d, it attaches to either right wheel group 5a, 5c and left wheel group 5b, 5d. It is specified whether the frame is transmitted from the transmitters 2a to 2d.

  Thereby, it is possible to specify the transmitters 2a to 2d of all four wheels 5a to 5d, and perform wheel position detection to specify which wheel 5a to 5d each transmitter 2a to 2d is attached to. Can do.

(Fourth embodiment)
A fourth embodiment of the present invention will be described. This embodiment is also a modification of the RSSI value comparison method with respect to the first to third embodiments, and is otherwise the same as the first to third embodiments, so the first to third embodiments. Only the parts different from the form will be described.

  In the first to third embodiments, from the transmitters 2a to 2d attached to both the front wheels 5a and 5b and the rear wheels 5c and 5d based on the difference in RSSI values between the frames for two periods. Identified whether the frame was transmitted. On the other hand, this specification may be performed based on a change in RSSI value in one frame.

  That is, as described above, the RSSI value of the frame sent for each period changes during frame transmission as the wheels 5a to 5d rotate. However, for the transmitters 2c and 2d attached to both rear wheels 5c and 5c close to the receiving antenna 31, the RSSI value remains constant, and the transmitter 2a attached to both front wheels 5a and 5b far from the receiving antenna 31. For 2b, the RSSI value changes. For this reason, if the RSSI value is a constant value, the frame is specified as being transmitted from the transmitters 2c and 2d attached to the rear wheels 5c and 5c. 5b can be identified as being transmitted from the transmitters 2a and 2b attached to 5b. The change in the RSSI value can be represented by the difference between the maximum value and the minimum value of the RSSI value in one frame, for example.

  Thus, based on the change of the RSSI value in one frame, the frame transmitted from the transmitters 2a to 2d attached to either the front wheels 5a, 5b or the rear wheels 5c, 5d is specified. You can also. And like the said 1st Embodiment, based on the rotation direction information stored in the transmission frame from each transmitter 2a-2d, it attaches to either right wheel group 5a, 5c and left wheel group 5b, 5d. It is specified whether the frame is transmitted from the transmitters 2a to 2d.

  Thereby, it is possible to specify the transmitters 2a to 2d of all four wheels 5a to 5d, and perform wheel position detection to specify which wheel 5a to 5d each transmitter 2a to 2d is attached to. Can do.

(Other embodiments)
In the above embodiment, the rear antenna 5c, 5d is compared with the transmitters 2a, 2b attached to the front wheels 5a, 5b by disposing the receiving antenna 31 of the receiver 3 closer to the rear of the vehicle 1. It is arranged near the transmitters 2c and 2d attached to the transmitter. On the other hand, as shown in FIG. 8, the entire receiver 3 may be disposed closer to the rear of the vehicle 1. Moreover, the receiver antenna 31 or the entire receiver 3 is not arranged near the rear of the vehicle 1, but the sensitivity of the receiver 3 is lowered by arranging it in a place near the front of the vehicle 1, for example, a front bumper. At this time, only the transmission frames from the transmitters 2a and 2b attached to both front wheels 5a and 5b may be received.

  In the above embodiment, as shown in FIG. 3, since the wheel position detection device is applied to the tire air pressure detection device, the rotational direction information of the wheels 5a to 5d is stored in the frame in which the information related to the tire air pressure is stored. To be sent. Thereby, wheel position detection and tire air pressure detection can be performed in a common frame. However, this is merely an example of the frame, and the frame for storing the rotation direction information and the frame for storing the information on the tire pressure may be separate frames.

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

Claims (8)

Applied to a vehicle (1) to which four wheels (5a-5d) with tires are attached to the vehicle body (6);
Wheel rotation direction detection means (22) provided on each of the four wheels (5a to 5d) and outputting a detection signal corresponding to the rotation direction of each of the four wheels (5a to 5d), and the wheel rotation direction detection A transmitter (2a to 2d) having a first control unit (23) that creates and transmits a frame including rotation direction information and unique identification information regarding the rotation direction detected by the means (22);
A receiving circuit (32) provided on the vehicle body (6) side for receiving frames transmitted from the transmitters (2a to 2d) via a receiving antenna (31), and data obtained from the received frames. Based on which of the four wheels (5a to 5d) the transmitter (2a to 2d) that has transmitted the frame is specified to which of the four wheels (5a to 5d) is attached. And a second control unit (33) for detecting the wheel position for storing the identification information of the transmitters (2a to 2d) provided to each of the four wheels (5a to 5d) in association with each other. (3)
At least the receiving antenna (31) of the receiver (3) has a distance from one of the front wheels (5a, 5b) and the rear wheels (5c, 5d) of the vehicle (1) from the other. It is arranged closer than the distance of
The reception circuit (32) measures the RSSI value of the received frame, and the reception level, which is the signal strength of the frame when received by the reception antenna (31), is up to a predetermined value. The RSSI value increases as the reception level increases. When the reception level exceeds a predetermined value, the RSSI value is measured as a constant value.
The second control unit (33) receives the frames transmitted from the transmitters (2a to 2d) provided on the four wheels (5a to 5d) when the wheel position is detected. From the rotation direction information included in the frame for four wheels, the frame is transmitted from the transmitter (2a, 2c) attached to either the right wheel (5a, 5c) or the left wheel (5b, 5d). And the frame where the RSSI value becomes a constant value is determined by the front wheels (5a, 5b) and the rear wheels (5c, 5d) based on the change of the RSSI value. Among them, it is determined that the frame is transmitted from the two wheels (5c, 5d) closer to the receiving antenna (31), and the frame in which the RSSI value changes is the front wheels (5a, 5b) and the Both rear wheels 5c and 5d), the transmitters (2a to 2d) are respectively connected to the four wheels by specifying that the signals are transmitted from the two wheels (5a, 5b) farther from the receiving antenna (31). A wheel position detecting device that identifies which of the two wheels (5a to 5d) is attached.   The wheel rotation direction detection means (22) detects acceleration in both directions perpendicular to the circumferential direction of the wheel (5a to 5d) when the wheel (5a to 5d) to which the transmitter (2a to 2d) is attached is rotated. The wheel position detecting device according to claim 1, wherein the wheel position detecting device is a two-axis acceleration sensor having an acceleration sensor (22a) for detecting acceleration and an acceleration sensor (22b) for detecting acceleration in both directions parallel to the circumferential direction.   The transmitters (2a to 2d) calculate a vehicle speed from accelerations detected by acceleration sensors (22a, 22b) included in the biaxial acceleration sensor, and transmit the frame when the vehicle speed reaches a predetermined vehicle speed. The wheel position detection device according to claim 1, wherein the wheel position detection device is performed.   The second control unit (33) is determined from the start of reception at the reception antenna (31) among a plurality of different frames transmitted from the same transmitter (2a to 2d) as a change in the RSSI value. The RSSI values at the same timing are compared with each other. If the RSSI values are constant, the reception antenna (31) of the front wheels (5a, 5b) and the rear wheels (5c, 5d) is used as the frame. ) That are transmitted from the two wheels (5c, 5d) closer to each other, and if there is a difference between the RSSI values, the front wheel (5a, 5b) and the rear wheels 4. The method according to claim 1, further comprising: transmitting from two wheels (5 a, 5 b) farther from the receiving antenna (31) of (5 c, 5 d). Suddenly Mounting the wheel position detecting device.   The second control unit (33) compares the RSSI values of a plurality of different frames transmitted from the same transmitter (2a to 2d) as changes in the RSSI value, and compares the RSSI value. If the maximum values of the two wheels are constant, the frame has two wheels (5c, 5d) closer to the receiving antenna (31) of the front wheels (5a, 5b) and the rear wheels (5c, 5d). ), And if there is a difference between the maximum RSSI values, the frame is received from the front wheels (5a, 5b) and the rear wheels (5c, 5d). 4. The wheel position detection device according to claim 1, wherein the wheel position detection device specifies that the transmission is made from two wheels (5 a, 5 b) farther from the antenna (31). 5.   The second control unit (33) compares the RSSI value minimum values of a plurality of different frames transmitted from the same transmitter (2a to 2d) as changes in the RSSI value, and compares the RSSI values with each other. If the minimum value is a constant value, the two frames (5c, 5c, 5d) of the front wheel (5a, 5b) and the rear wheels (5c, 5d) closer to the receiving antenna (31) 5d), and if there is a difference between the minimum values of the RSSI values, the frame is the front wheel (5a, 5b) and the rear wheels (5c, 5d). 4. The wheel position detecting device according to claim 1, wherein the wheel position detecting device identifies that the wheel is transmitted from two wheels (5 a, 5 b) far from the receiving antenna (31). 5. .   The second control unit (33) compares the RSSI value change in one frame of the frames transmitted from the transmitters (2a to 2d) as the RSSI value change, and the RSSI value is constant. If it is a value, the frame is transmitted from the two wheels (5c, 5d) closer to the receiving antenna (31) of the front wheels (5a, 5b) and the rear wheels (5c, 5d). If there is a change in the RSSI value, the frame is divided into two of the front wheels (5a, 5b) and the rear wheels (5c, 5d) that are far from the receiving antenna (31). The wheel position detection device according to any one of claims 1 to 3, wherein the wheel position detection device is specified to be transmitted from a wheel (5a, 5b). A tire pressure detecting device including the wheel position detecting device according to any one of claims 1 to 7,
The transmitters (2a to 2d) include a sensing unit (21) that outputs a detection signal corresponding to the tire pressure provided on each of the four wheels (5a to 5d), and the first control unit ( 23) storing information on tire air pressure obtained by signal-processing the detection signal of the sensing unit (21) in a frame, and transmitting the frame to the receiver (3);
The receiver (3) detects the air pressure of the tire provided in each of the four wheels (5a to 5d) from the information related to the tire air pressure in the second control unit (33). A tire pressure detecting device.

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