JP2013184490A - Tire information obtaining device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption of each of detecting units while maintaining fine signal reception condition at a monitoring unit even when the detection units are located at an arbitrary rotation angle while tires are rotating.SOLUTION: A microprocessor 104 reads correction information on transmission power out of a correction information memory circuit 105, the transmission power being set in correspondence to a rotation angle of a tire so that an input signal level at a monitoring unit is within a given allowable range in an input signal level range in which the monitoring unit can receive a signal properly, and supplies the read correction information to a transmitting circuit 106. Based on the correction information, the transmitting circuit 106 then corrects the transmission power according to a rotation angle of the tire and transmits information of the correction. As a result, the power of a radio wave transmitted from a detecting unit is changed according to an angle of rotation of the detecting unit caused by the rotation of the tire during traveling of a vehicle. This leads to a reduction in battery power consumption.

Description

  The present invention relates to a tire information acquisition device, and in particular, a plurality of detection units that are attached to rims in each tire and transmit the detection results of tire information to the outside by radio waves, and are provided in a vehicle body and transmitted from each detection unit. The present invention relates to a tire information acquisition device including a monitoring unit that receives the detection result.

  Conventionally, inspection of a physical state of a tire such as tire air pressure is an indispensable work for safe driving of a vehicle. However, since it takes time and labor to manually inspect tires, a tire information acquisition device that automatically detects the physical state of tires such as air pressure has been developed and started to be used in general vehicles.

  The tire information acquisition device generally includes a detection unit that is mounted on a tire to detect a physical state of the tire and wirelessly transmits the detection result, and a monitoring unit that receives data transmitted from the detection unit. It is composed of The detection unit is generally provided inside the tire and is often fixed to the rim or embedded in the tire.

  As an example, a tire pressure detecting device disclosed in Japanese Patent Laid-Open No. 2005-321958 (Patent Document 1) is known. This device includes a transmitter having a sensor in each tire and a receiver provided in the vehicle body. The transmitter detects the tire air pressure, and the detection signal data indicating the detection result in the transmission frame. Store and send. The receiver is attached to the vehicle body side of the vehicle, receives the transmission frame transmitted from the transmitter, and performs various processes and calculations based on the detection signal stored in the tire. Find the air pressure.

  Furthermore, in the device disclosed in Patent Document 1, if there is a position where the reception level at the receiver is less than the required level due to the rotation of the tire, even if the transmitter transmits radio waves at that position, the receiver side Since it becomes impossible to receive this, which causes a decrease in the reception rate at the receiver in the tire pressure detection device, in order to avoid this, based on the detection signal of the acceleration sensor provided in the transmitter, The transmitter position is detected, and when the detected transmitter position is included in the receivable range of the antenna in the receiver is set as the transmission timing, the detection signal is transmitted to the receiver through the transmitter. ing.

  As another example, a tire information management system disclosed in Japanese Patent Laid-Open No. 2008-087704 (Patent Document 2) is known. In this system, in order to manage the tires of a running vehicle such as a construction vehicle, a sensor module for measuring a tire state quantity such as a tire pressure is attached to the inner surface of the tire, and the measurement data transmitted from the sensor module Etc. are received by the vehicle body side module, and based on this signal, the driver is informed of the abnormality of the tire and is used for management of the tire usage status and the like.

  Further, in the system disclosed in Patent Document 2, in order to reduce the power consumption of the sensor module, the sensor module is provided with transmission radio wave intensity control means for controlling the transmission radio wave intensity in data transmission. The vehicle-side module is configured to control the transmission radio field intensity in the next data transmission based on the transmission radio field intensity setting value received from the reception module, and the vehicle-side module receives the reception radio wave of the data signal transmitted from the sensor module for each sensor module. In addition to providing reception radio field strength measurement means to measure the strength, a transmission radio field strength setting value is created according to the reception radio field intensity of the data signal transmitted from the sensor module last time. It is comprised so that it may add to the command to a sensor module.

JP 2005-321958 A JP 2008-087704 A

  In the apparatus described in Patent Document 1, data is transmitted from the transmitter only when the transmitter is located within a range that can be satisfactorily received by the receiver. However, the rotational speed of the tire depends on the traveling speed of the vehicle. Since it changes greatly, it is difficult to determine the data transmission timing in consideration of the data transmission interval and the rotational position of the transmitter. Furthermore, the apparatus of Patent Document 1 does not consider anything about the reduction of data transmission power. For this reason, the lifetime of the battery provided in the transmitter may be shortened.

  In the system described in Patent Document 2, an attempt is made to reduce the power consumption of the sensor module, but there is no detailed description on how to control the transmission radio wave intensity in the next data transmission. That is, when the tire rotates while the vehicle is running, the sensor module also rotates with the rotation of the tire. Therefore, the received radio wave intensity at the receiver changes depending on the rotational position of the sensor module. For this reason, it is not known how to control the transmission radio wave intensity in the senna module to reduce the power consumption of the sensor module while maintaining a good reception state in the receiver. That is, as described in Paragraph 0032 of Patent Document 2, “Pmin is a transmission radio wave intensity at which communication with the vehicle body side module 5 becomes impossible below this value”, the transmission radio wave intensity depends on the rotational position of the tire. It is clear that there are cases where reception is possible and impossible when Pmin.

  The present invention provides a tire information acquisition device capable of reducing power consumption in each detection unit while maintaining a good reception state in the monitoring unit even when the tire is rotating and the detection unit exists at an arbitrary rotation angle. It is to provide.

  In order to achieve the above object, the present invention provides a first sensor that is provided in a tire of a vehicle and detects its own rotation angle as the tire rotates, and a second sensor that detects a predetermined physical quantity of the tire as tire information, A detection unit that has at least a transmission unit that transmits a detection result of the second sensor by radio waves and a battery in a predetermined housing and operates by power supplied from the battery, and the detection result transmitted from the detection unit In a tire information acquisition device comprising a monitoring unit that receives a received signal, a received signal level that is higher than a minimum receivable received signal level within a range of a received signal level by which the monitored unit can satisfactorily receive the monitored unit. The vehicle is set within a predetermined allowable range centered on the reference level with the level as the reference level. Suggest tire information obtaining apparatus having a transmission power changing means for changing the power of the radio wave transmitted from the sensing unit in accordance with the rotation angle of the detection unit with the rotation of the tire at the time line.

  According to the tire information acquisition device of the present invention, the vehicle travels by the transmission power varying means so that the received signal level by the monitoring unit falls within a predetermined allowable range within the range of the received signal level that can be satisfactorily received by the monitoring unit. The electric power of the radio wave transmitted from the detection unit is changed according to the rotation angle of the detection unit accompanying the rotation of the tire at the time.

  Thereby, the signal transmitted from each detection unit is always stably received by the monitoring unit, and the transmission power in the detection unit is reduced as compared with the conventional case.

  Since the battery consumption can be greatly reduced by the present invention, the size and capacity of the battery, which is the most heavy component in the detection unit of the tire information acquisition device, can be reduced, and the weight can be reduced. Especially for passenger cars, unlike the tires for trucks and buses, the electric field strength is much higher than the reception limit because there is little influence of the electric wave attenuation by the steel carcass and the electric wave can be transmitted, and this method greatly wastes battery consumption. Can be suppressed.

1 is an external view showing the arrangement of detection units and monitoring units in an embodiment of the present invention. The figure which shows the structure of the tire information acquisition apparatus in one Embodiment of this invention. The figure explaining the installation place of the detection unit to the tire in one embodiment of the present invention The figure explaining the installation place of the detection unit to the tire in one embodiment of the present invention The block diagram which shows the structure of the detection unit in one Embodiment of this invention. The block diagram which shows the structure of the monitoring unit in one Embodiment of this invention. Measured results of acceleration in the Z-axis direction in one embodiment of the present invention Measured results of acceleration in the Z-axis direction in one embodiment of the present invention Measured results of acceleration in the Z-axis direction in one embodiment of the present invention Measured result of acceleration in X-axis direction in one embodiment of the present invention Measured result of acceleration in X-axis direction in one embodiment of the present invention Measured result of acceleration in X-axis direction in one embodiment of the present invention The figure which shows the relationship of the gravity acceleration superimposed on the acceleration in the Z-axis direction, and the gravity acceleration which squared the acceleration of the X-axis direction in one Embodiment of this invention The flowchart showing the test signal emission process which the microprocessor of the detection unit in one Embodiment of this invention performs The flowchart showing the correction information setting process which the microprocessor of the detection unit in one Embodiment of this invention performs The figure which shows an example of the correction information in one Embodiment of this invention The figure which shows an example of the correction information in one Embodiment of this invention The flowchart showing the normal process which the microprocessor of the detection unit in one Embodiment of this invention performs The flowchart showing the test signal emission instruction | indication process and correction information setting process which the microprocessor of the monitoring unit in one Embodiment of this invention performs The flowchart showing the normal process which the microprocessor of the monitoring unit in one Embodiment of this invention performs The figure which shows the reception level of the signal which the monitoring unit in one Embodiment of this invention received from the detection unit of each tire. The figure which shows the setting value of the reception limit level and reception tolerance in one Embodiment of this invention The figure explaining the transmission timing of the detection unit in one Embodiment of this invention The figure which shows the ratio of the consumption current of the detection unit in one Embodiment of this invention. The figure explaining reduction of the consumption current of the detection unit in one Embodiment of this invention

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  The tire information acquisition device according to the present embodiment includes a detection unit provided in each tire that wirelessly transmits tire information such as tire air pressure and temperature and a monitoring unit provided in the vehicle body, and changes according to the rotation of the tire. The radio wave transmission intensity is corrected so that the radio wave intensity from the detection unit can be always received by the monitoring unit.

  A tire information acquisition device is a system that generally transmits data from a detection unit installed in a tire and receives and displays the data with a monitoring unit installed in a driver's seat or the like. Since the position of the detection unit changes as the tire rotates while the vehicle is running, a phenomenon occurs in which the level of the received electric field strength varies according to the rotation of the tire. Depending on the timing of data transmission, the data may be transmitted at a low electric field strength level. Therefore, it is essential to increase the radio wave transmission intensity so that radio waves can be received even in the lowest level, but there is a problem that the current consumption of the detection unit increases.

  In order to solve this problem, in the present embodiment, the detection unit is provided with a sensor that detects the rotation angle of the tire, and the radio wave transmission intensity is appropriately changed as needed depending on the electric field intensity that varies depending on the rotation angle of the tire. It was possible to receive stably and to reduce the current consumption during transmission and to extend the battery life.

  In the present embodiment, an example in which the tire information acquisition device of the present invention is mounted on a four-wheel vehicle will be described as an example.

  FIG. 1 is an external view showing the arrangement of detection units and monitoring units in a tire information acquisition apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing the configuration of the tire information acquisition apparatus according to an embodiment of the present invention. FIG. 4 is a diagram for explaining the installation location of the detection unit on the tire in one embodiment of the present invention, FIG. 5 is a block diagram showing the configuration of the detection unit in one embodiment of the present invention, and FIG. 6 is one embodiment of the present invention. It is a block diagram which shows the structure of the monitoring unit in a form.

  1 to 3, 1 is a vehicle, 2 is a tire (wheel), 3 is an axle, 4 is a tire house, 100 is a detection unit, and 200 is a monitoring unit. In the present embodiment, in each of the detection unit 100 and the monitoring unit 200, each electric system circuit is housed in a small casing having insulation and electromagnetic wave transmission, and each of the four detection units 100 is a tire of the vehicle 1. 2 and one monitoring unit 200 is arranged in the vicinity of the driver's seat. In the present embodiment, the detection unit 100 and the monitoring unit 200 constitute the tire information acquisition device of the present invention.

  The tire 2 is, for example, a known tubeless radial tire, and includes a wheel and a rim in the present embodiment. The tire 2 includes a tire main body 305, a rim 306, and a wheel 307. The tire main body 305 includes a known cap tread 301, under tread 302, belts 303A and 303B, carcass 304, and the like. In the present embodiment, as shown in FIG. 3, the tire 2 includes a detection unit 100, and the detection unit 100 is fixed to the rim 306.

  In the present embodiment, the following description will be made assuming that the rotation direction of the tire 2 is the X-axis direction, the rotation axis direction of the tire 2 is the Y-axis direction, and the radial direction centering on the rotation axis of the tire 2 is the Z-axis direction. In the present embodiment, the detection unit 100 is fixed to the rim 306 of the tire 2. However, the attachment position of the detection unit 100 is not limited to the rim 306, and may be any part of the tire / wheel. Good.

  As shown in FIG. 5, the detection unit 100 includes a pressure sensor 101, a temperature sensor 102, a rotational position detection sensor 103, a microprocessor 104, a correction information storage circuit 105, a transmission circuit 106, a reception circuit 107, an antenna switching circuit 108, an antenna. 109 and a battery 110.

  The pressure sensor 101 detects the air pressure in the tire 2 and outputs an electric signal corresponding to the value of the air pressure.

  The temperature sensor 102 detects the temperature in the tire 2 and outputs an electrical signal corresponding to the temperature value.

  The rotational position detection sensor 103 is a sensor for detecting the rotational position (rotational angle) of the detection unit 100 in the tire 2, and the first acceleration generated in the X-axis direction, which is the rotational direction of the tire 2, and the tire 2. Based on one sensor element (not shown) that detects the second acceleration generated in the Z-axis direction, which is the radial direction around the rotation axis 3, and outputs it as an electrical signal, and the electrical signal output from this sensor element And an interface unit (not shown) for outputting information corresponding to the acceleration value to the microprocessor 104. In this embodiment, the rotation position (rotation angle) is obtained by detecting the acceleration in the X and Z axis directions by the sensor element. However, the acceleration in the X, Y, and Z axis directions is detected by using the sensor element. The rotation position (rotation angle) may be obtained. In the present embodiment, the rotation position (rotation angle) of the tire is detected using the acceleration sensor. However, the present invention is not limited to this, and for example, the rotation position (the geomagnetic sensor or the gyro sensor is used). (Rotation angle) may be detected.

  The microprocessor 104 is composed mainly of a well-known CPU, and includes a memory for storing a program for operating the CPU, an arithmetic memory, and the like. Further, the microprocessor 104 inputs output signals of the pressure sensor 101, the temperature sensor 102, and the rotational position detection sensor 103, and in normal processing, pressure information, temperature information, and rotational position (rotation angle) information are obtained from these signals. For example, it is acquired every 3 seconds, these information is accumulated corresponding to the passage of time, and the information is converted into a digital signal of a predetermined format together with identification information unique to itself stored in advance. The data is transmitted to the monitoring unit 200 via the transmission circuit 106 every predetermined time, for example, every 3 minutes. At this time, the transmission circuit 106 inputs the correction information stored in the correction information storage circuit 105 via the microprocessor 104, and transmits information with the transmission power obtained by correcting the maximum transmission power based on the correction information.

  Further, the microprocessor 104 receives a test signal emission instruction from the monitoring unit 200, and when the received test signal emission instruction includes its own identification information, a test signal emission process, which will be described later, is different from the normal process. And correction information setting processing. Through these processes, the correction information is stored in the correction information storage circuit 105.

  The correction information storage circuit 105 is composed of a rewritable nonvolatile memory, in which the transmission limit time t1 and the transmission interval time t2 of the test information necessary for the test information emission process are stored in advance, and all the correction information in the initial state The correction information that the transmission power correction amount becomes 0 at the rotation angle is stored, but the transmission power correction information in which a predetermined correction amount is set for each rotation angle by the correction information setting process is stored. . In this embodiment, the transmission limit time t1 is set to 60 seconds and the transmission interval time t2 is set to 6 seconds so that the transmission power correction amount for each rotation angle of the tire can be calculated. However, the present invention is not limited to this and may be set as appropriate.

  The transmission circuit 106 transmits the digital signal input from the microprocessor 104 from the antenna 109 with a radio wave of a predetermined frequency, for example, a radio wave of 315 MHz. In the test signal emission process, a signal is transmitted at the maximum transmission power, and after the test signal emission process and the correction information setting process are performed, based on the correction information stored in the correction information storage circuit 105. To correct the transmission power and transmit the signal.

  The receiving circuit 107 receives the signal transmitted from the monitoring unit 200 and outputs the received information to the microprocessor 104.

  The antenna switching circuit 108 connects the antenna 109 to either the output terminal of the transmission circuit 106 or the input terminal of the reception circuit 107 by a switching signal output from the microprocessor 104.

  The battery 110 supplies driving power to each sensor and each circuit included in the detection unit 100.

  As shown in FIG. 6, the monitoring unit 200 includes an antenna 201, an antenna switching circuit 202, a receiving circuit 203, a transmitting circuit 204, a microprocessor 205, a display circuit 206, an alarm buzzer 207, an alarm lamp 208, a storage unit 209, an operation The unit 210 and the DC / DC conversion circuit 211 are configured.

  The antenna switching circuit 202 connects the antenna 201 to either the input terminal of the reception circuit 203 or the output terminal of the transmission circuit 204 by a switching signal output from the microprocessor 205.

  The receiving circuit 203 receives the radio wave transmitted from the detection unit 100 via the antenna 201, outputs the value of the received radio wave signal strength (reception level) to the microprocessor 205, and also receives the received information as a digital signal. Reproduce and output to the microprocessor 205.

  The transmission circuit 204 transmits the digital signal input from the microprocessor 205 from the antenna 201 using radio waves of a predetermined frequency, for example, 315 MHz radio waves.

  The microprocessor 205 inputs pressure information, temperature information, and acceleration information from the receiving circuit 202, displays the pressure information and temperature information on the display of the display circuit 206, and when the pressure value exceeds a predetermined threshold or temperature When the value of exceeds the predetermined threshold, the alarm buzzer 207 is sounded and the alarm lamp 208 is turned on. Further, the microprocessor 205 inputs the value of the reception level from the reception circuit 203 and records the reception level for each rotation angle within a predetermined time.

  In the test signal emission process, the microprocessor 205 records the reception level of the radio wave transmitted from the detection unit 100 after transmitting the test signal emission instruction specifying the identification information for each rotation angle, and sets the correction information. In the processing, correction information corresponding to the detection unit 100 to be corrected information setting is calculated using the received reception level for each rotation angle and the reception limit level value stored in the storage unit 209, and this correction information is calculated. Is transmitted to the detection unit 100.

  In the storage unit 209, identification information of all the detection units 100 mounted on the tire 2 of the vehicle 1 is stored corresponding to the positions of the tires on which the detection unit 100 is mounted. A permissible range of air pressure (allowable minimum value and permissible maximum value), a permissible maximum value of the tire air temperature, and a value of the minimum reception level (reception limit level value) that can be received by the monitoring unit 200 are stored in advance. For example, −105 dBm is stored in the storage unit 209 as the value of the reception limit level. Further, the storage unit 209 falls within a predetermined allowable range (for example, −95 dBm ± 1 dBm) centered on the reference level with a reception signal level (for example, −95 dBm) higher than the reception limit level as a reference level. As described above, the allowable reception range is set.

  The operation unit 210 includes a plurality of switches, and outputs on / off signals of these switches to the microprocessor 205.

  The DC / DC conversion circuit 211 is supplied with electric power from an in-vehicle DC power supply (not shown), and this voltage is supplied to the antenna switching circuit 202, the reception circuit 203, the transmission circuit 204, the microprocessor 205, the display circuit 206, and the alarm buzzer 207. The warning light 208, the storage unit 209, and the operation unit 210 are converted into voltages for driving, and drive power is supplied to them.

  Next, the operation of the rotation position (rotation angle) acquisition process in the detection unit 100 will be described with reference to the drawings. 7 to 9 show actual measurement results of acceleration in the Z-axis direction, and FIGS. 10 to 12 show actual measurement results of acceleration in the X-axis direction. In addition, the minute vibration component which generate | occur | produces by the friction between a driving | running | working road surface and the tire 2 is superimposed on the signal waveform of each figure.

  7 to 9, FIG. 7 is an actual measurement value of acceleration in the Z-axis direction when traveling at a speed of 2.5 km, FIG. 8 is an actual measurement value of acceleration in the Z-axis direction when traveling at a speed of 20 km, and FIG. This is an actual measurement value of acceleration in the Z-axis direction when traveling at a speed of 40 km / h. Thus, since the centrifugal force of the wheel increases as the traveling speed increases, the acceleration in the Z-axis direction also increases. Also, gravitational acceleration is superimposed on the acceleration in the Z-axis direction.

  10 to 12, FIG. 10 is an actual measurement value of acceleration in the X-axis direction when traveling at a speed of 2.5 km / h, and FIG. 11 is an actual measurement value of acceleration in the X-axis direction when traveling at a speed of 20 km / h. 12 is an actual measurement value of acceleration in the X-axis direction during traveling at a speed of 40 km / h. Thus, since the rotation speed of the wheel increases as the traveling speed increases, the cycle in which the acceleration in the X-axis direction changes becomes shorter. Moreover, in the figure, the reason why the actually measured value has a sine wave shape is that gravitational acceleration is superimposed as described above. Therefore, the rotation position (rotation angle) of the detection unit 100 can be obtained from the gravity acceleration superimposed on the acceleration in the X-axis direction and the gravity acceleration superimposed on the acceleration in the Z-axis direction. That is, as shown in FIG. 13, the magnitude of the gravitational acceleration component Ax superimposed on the acceleration in the X-axis direction and the magnitude of the gravitational acceleration component Az superimposed on the acceleration in the Z-axis direction change to sine wave shapes, respectively. Since a phase difference of 90 degrees is generated in the rotation angle, the rotation position (rotation angle) of the detection unit 100 can be obtained by comparing these.

  Next, the operation of the tire information acquisition apparatus according to this embodiment having the above-described configuration will be described with reference to the flowcharts shown in FIGS. 14 to 20 and the diagrams showing the correction information. 14 represents a test signal emission process performed by the microprocessor 104 of the detection unit 100, the flowchart of FIG. 15 represents a correction information setting process performed by the microprocessor 104 of the detection unit 100, and FIGS. 16 and 17 illustrate correction information. FIG. 18 is a flowchart illustrating normal processing performed by the microprocessor 104 of the detection unit 100, and FIG. 19 is a flowchart illustrating test signal emission instruction processing and correction information setting processing performed by the microprocessor 205 of the monitoring unit 200. 20 represents a normal process performed by the microprocessor 205 of the monitoring unit 200.

  The test signal emission process and the correction information setting process in the detection unit 100 are started when an operator (such as a driver of the vehicle) pushes an initial setting switch (not shown) of the monitoring unit 200 while driving the vehicle. The monitoring unit 200 and the detection unit 100 automatically perform normal processing when the test signal emission processing and the correction information setting processing are completed.

  In the initial state, the detection unit 100 performs normal processing.

  When the microprocessor 104 of the detection unit 100 receives a test signal emission instruction including its own identification information from the monitoring unit 200, the microprocessor 104 starts a test signal emission process.

  In the test signal emission process, as shown in the flowchart of FIG. 14, the microprocessor 104 of the detection unit 100 sets the transmission power in the transmission circuit 106 to the maximum transmission power (SA1), and the correction information storage circuit 105 is rewritable. It consists of a non-volatile memory, and reads the transmission interval time t2 and the transmission limit time t1 from the correction information storage circuit 105 (SA2).

  Next, the microprocessor 104 resets the first timer time T1 to start measuring time (SA3) and resets the second timer time T2 to start measuring time (SA4). Thereafter, the rotation angle is acquired from the detection result of the rotation position detection sensor 103 (SA5), and test information including information on the rotation angle and its own identification information is transmitted (SA6).

  Next, the microprocessor 104 determines whether or not the second timer time T2 has reached the transmission interval time t2 (SA7), and when the second timer time T2 has reached the transmission interval time t2, It is determined whether or not the timer time T1 of 1 has reached the transmission limit time t1 (SA8). As a result of this determination, when the first timer time T1 does not reach the transmission limit time t1, the process proceeds to SA4. When the first timer time T1 reaches the transmission limit time t1, the monitoring unit 200 Test end information is transmitted to (SA9), and the test signal emission processing is ended.

  In the correction information setting process, as shown in the flowchart of FIG. 15, the microprocessor 104 of the detection unit 100 monitors whether or not the correction information transmitted from the monitoring unit 200 is received via the receiving circuit 107 (SB1). ), After receiving the correction information, the received correction information is stored in the correction information storage circuit 105.

  An example of the correction information stored in the correction information storage circuit 105 is shown in the tables of FIGS. In this example, for example, when the angle (rotation angle) is 20 degrees, the reception level at the monitoring unit 220 when the detection unit 100 transmits at the maximum transmission power is −94 dBm, so the reception level is −95 dBm. Since the reception level in the monitoring unit 220 when the detection unit 100 transmits at the maximum transmission power when the angle (rotation angle) is 90 degrees is −84 dBm, The correction amount for making the reception level −95 dBm is −11 dBm. In this embodiment, since the minimum receivable level that can be received is −105 dBm, an average reception level of −95 dBm that is 10 dBm larger than the minimum receivable level that can be received in order to obtain a stable reception state is obtained. The transmission power of the detection unit 100 is corrected.

  In the normal process, as shown in the flowchart of FIG. 18, the microprocessor 104 of the detection unit 100 clears the accumulated information (SC1), resets the third timer time T3, and starts timekeeping (SC2). . Thereafter, the microprocessor 104 acquires pressure information from the pressure sensor 101 every time t4, acquires temperature information from the temperature sensor 102, and acquires a rotation angle based on acceleration information from the rotation position detection sensor 103. These pieces of information are stored in the memory corresponding to the passage of time (SC3). Further, the microprocessor 104 determines whether or not the time T3 of the third timer has passed the predetermined transmission interval time t5 along with the accumulation of information (SC4), and is stored in advance when the transmission interval time t5 has elapsed. The pressure information, the temperature information, and the accumulated information of the rotation angle are converted into a digital signal of a predetermined format together with the identification information unique to itself and transmitted to the monitoring unit 200 via the transmission circuit 106 (SC5). That is, the detection unit 100 transmits information to the monitoring unit 200 every 3 minutes.

  In the present embodiment, the time t4 and the time t5 are stored in advance in the memory of the microprocessor 104. In the present embodiment, the time t4 is set to 3 seconds, and the transmission interval time t5 is set to 3 minutes. Yes.

  In the initial state, the monitoring unit 200 performs normal processing.

  Further, when an initial setting switch (not shown) of the operation unit 210 is pressed, the microprocessor 205 of the monitoring unit 200 starts a test signal emission instruction process and a correction information setting process.

  In the test signal emission instruction process and the correction information setting process, as shown in the flowchart of FIG. 19, the microprocessor 205 of the monitoring unit 200 sequentially stores identification information of all the detection units 100 attached to the vehicle from the storage unit 209. Reading is performed, and a test signal emission instruction process and a correction information setting process are performed on each detection unit 100.

  That is, the microprocessor 205 of the monitoring unit 200 reads the identification information of the detection unit 100 from the storage unit 209 (SD1), and transmits a test signal emission instruction including this identification information via the transmission circuit 204 (SD2).

  Thereafter, the test information transmitted from the detection unit 100 corresponding to the identification information is received, the identification information included in the test information is confirmed to be the specified identification information, and included in the test information. The received rotation angle information is acquired, the reception level of the received signal is acquired from the reception circuit 203, and the reception level and the rotation angle are associated with each other for each identification information and stored in the storage unit 209 (SD3).

  Next, the microprocessor 205 determines whether or not the test end information is received from the detection unit 100, and repeats the process of SD3 until the test end information is received from the detection unit 100. When the test end information is received from the detection unit 100, the microprocessor 205 confirms the identification information included in the test end information, and the reception level and rotation stored in the storage unit 209 corresponding to this identification information. Correction information is calculated from the angle (SD5).

  Next, the microprocessor 205 transmits the identification information of the detection unit 100 and the calculated correction information to the detection unit 100 (SD6).

  By performing the processes of SD1 to SD6 on each detection unit 100, transmission power correction information can be stored in each detection unit 100.

  In the normal processing, as shown in the flowchart of FIG. 20, the microprocessor 205 of the monitoring unit 200 monitors whether or not the initial setting switch of the operation unit 210 is pressed (SE1), and the initial setting switch is pressed. If so, the test signal emission instruction process and the correction information setting process are performed, and then the process proceeds to SE1. When the initial setting switch is not pressed, the microprocessor 205 receives information transmitted from each detection unit 100 (SE2), extracts tire pressure information and temperature information from the received information, and displays the display circuit 206. (SE3).

  Next, the microprocessor 205 determines whether or not the received pressure value is within the allowable range (SE4). As a result of this determination, if the received pressure value is not within the allowable range, the process proceeds to SE6 described later. If the received pressure value is within the allowable range, the received temperature value is allowable. It is determined whether or not the maximum value is exceeded (SE5). When the received temperature value does not exceed the allowable maximum value, the process proceeds to SE1. When the received temperature value exceeds the allowable maximum value, The display circuit 206 indicates that an abnormality has occurred in the pressure or temperature of the tire (SE6), and an alarm buzzer is sounded (SE7), and an abnormality occurs in the alarm light provided for each tire. The warning light corresponding to the tire that has been burned is turned on (SE8).

  By performing the processing described above, the power consumption in each detection unit 100 can be reduced as compared with the conventional case. That is, FIG. 21 shows the reception level when the monitoring unit 200 receives a radio wave transmitted with the maximum transmission power from the detection unit 100 attached to each tire. Thus, the reception level in the monitoring unit 200 differs depending on the detection units 100 provided in the front, rear, left and right tires.

  Further, as shown in FIG. 22, in this embodiment, if a reception level of −95 dBm, which is 10 dBm larger than the minimum reception level (reception limit level) −105 dBm that can be received in order to obtain a stable reception state, can be obtained on average. Since it is good, it can be seen that when the transmission is performed with the maximum transmission power, the reception level is considerably higher than −95 dBm and wasteful transmission power is consumed. For this reason, by correcting the transmission power of the detection unit 100 so that the reception level in the monitoring unit 200 is within an allowable range E of, for example, ± 1 dBm centered at −95 dBm, waste of transmission power can be reduced and the battery life is extended. be able to.

  In addition, the transmission limit time t1 and the transmission interval time t2 used for the test signal emission processing in the detection unit 100 can be freely set in the correction information storage circuit 105 of the detection unit 100. It is preferable to do. For example, as shown in FIG. 23, when the transmission interval time t2 is set to 30 seconds and the vehicle travels at a speed of 30 km / h, information can be obtained for each rotation angle of about 130 degrees.

  As shown in FIG. 24, the ratio of the battery current consumption in the detection unit 100 is 8.4% when the microprocessor 104 is in the sleep state, 4.5% when the pressure / temperature is measured, and 72. 2% and others are 15.1%, which consumes the largest amount of current during radio transmission.

  By correcting the transmission power of the detection unit 100 as described above, current consumption during wireless transmission can be reduced. That is, as shown in FIG. 25, when the current consumption in the sleep state is considered as a reference, the current consumption increases by 4 mA in the pressure / temperature measurement than in the sleep state. In addition, during wireless transmission, the current consumption increases by 20 mA than in the sleep state. Here, for example, when the transmission radio wave intensity is lowered by 8 dBm, the current consumption during wireless transmission is reduced from 20 mA to 14 mA, and the transmission current can be reduced by 30%. As described above, the current consumed by the detection unit 100 is the largest at the time of wireless transmission and occupies 70% or more. Therefore, it is possible to significantly extend the battery life by reducing the wireless transmission current.

  Therefore, since the battery consumption of the detection unit can be greatly reduced by this embodiment, the size and capacity of the battery, which is the most heavy component in the detection unit of the tire information acquisition device, can be reduced, and the weight can be reduced. Become. Especially for passenger cars, unlike the tires for trucks and buses, the electric field strength is much higher than the reception limit because there is little influence of the electric wave attenuation by the steel carcass and the electric wave can be transmitted, and this method greatly wastes battery consumption. Can be suppressed.

  In this embodiment, the correction value of the transmission power is automatically set to each detection unit 100 by pressing the initial setting switch of the monitoring unit 200. However, the correction value is stored in each detection unit 100 in advance. In addition, the transmission power may be changed according to the stored correction value.

  In the present embodiment, the detection unit 100 transmits a signal with the maximum transmission power in the test signal emission process, but the present invention is not limited to this.

  It consists of a plurality of detection units that are mounted on the rim in each tire and transmit the detection results of tire information to the outside by radio waves, and a monitoring unit that is provided in the vehicle body and receives the detection results transmitted from each detection unit The battery consumption of the detection unit in the tire information acquisition device can be reduced as compared with the conventional case.

  DESCRIPTION OF SYMBOLS 1 ... Vehicle, 2 ... Tire, 3 ... Axle, 4 ... Tire house, 100 ... Detection unit, 101 ... Pressure sensor, 102 ... Temperature sensor, 103 ... Rotation position detection sensor, 104 ... Microprocessor, 105 ... Correction information storage circuit , 106 ... transmission circuit, 107 ... reception circuit, 108 ... antenna switching circuit, 109 ... antenna, 110 ... battery, 200 ... monitoring unit, 201 ... antenna, 202 ... antenna switching circuit, 203 ... reception circuit, 204 ... transmission circuit, 205 ... microprocessor, 206 ... display circuit, 207 ... alarm buzzer, 208 ... alarm lamp, 209 ... storage unit, 210 ... operation unit, 211 ... DC / DC conversion circuit, 301 ... cap toledo, 302 ... under tread, 303A, 303B ... Belt, 304 ... Carcass, 305 ... Tire body, 306 ... Rim, 307 ... Wheel.

Claims (5)

A first sensor that is provided on the tire of the vehicle and detects a rotation angle of the tire as the tire rotates, a second sensor that detects a predetermined physical quantity of the tire as tire information, and at least a detection result of the second sensor is transmitted by radio waves. Tire information acquisition apparatus comprising: a detection unit that includes a transmission unit and a battery in a predetermined housing and operates by power supplied from the battery; and a monitoring unit that receives the detection result transmitted from the detection unit In
The reception signal level by the monitoring unit is within a range of the reception signal level at which the monitoring unit can satisfactorily receive, and a predetermined reception signal level that is higher than the lowest receivable reception signal level by a predetermined level is set as a reference level. A transmission power varying means is provided for changing the power of the radio wave transmitted from the detection unit in accordance with the rotation angle of the detection unit accompanying the rotation of the tire when the vehicle is running so as to be within an allowable range. Tire information acquisition device. The detection unit is
The reception signal level by the monitoring unit is within a range of the reception signal level at which the monitoring unit can satisfactorily receive. Correction amount storage means in which the correction amount of the transmission power value is stored in advance corresponding to the rotation angle of the detection unit accompanying the rotation of the tire during vehicle travel so as to be within the allowable range;
The transmission circuit having means for correcting the transmission power value based on the correction amount stored in the correction amount storage means and transmitting the detection result;
The tire information acquiring apparatus according to claim 1, wherein the transmission power varying unit includes the correction amount storage unit and the transmission circuit. The transmission power variable means is
Provided in the monitoring unit,
Test signal emission instructing means for transmitting to the detection unit a test signal emission instruction for instructing to emit a test signal including information on the rotation angle at a plurality of rotation angles at which the detection unit is located;
Signal level recording means for recording the received signal level of the test signal transmitted from the received detection unit in correspondence with the rotation angle;
A reference level storage means for storing a predetermined permissible range centered on the reference level in correspondence with the rotation angle, with a low predetermined received signal level within the range of the received signal level that can be satisfactorily received as a reference level; ,
Based on the received signal level recorded in the signal level recording means and the signal level stored in the reference level storage means, the value of the received signal level is within a predetermined allowable range centered on the reference level. Correction amount calculation means for calculating a correction amount of the transmission power of the detection unit in correspondence with the rotation angle so as to be a value;
Correction amount setting means for transmitting information on the correction amount of the transmission power corresponding to the rotation angle calculated by the correction amount calculation means to the detection unit;
Provided in the detection unit,
Test signal emission means for emitting a test signal of a predetermined reference transmission power including information on the rotation angle at a plurality of rotation angles after receiving the test signal emission instruction from the monitoring unit;
Correction amount storage means for storing information on the correction amount of the transmission power received from the monitoring unit;
Transmission power control means for changing the transmission power according to the rotation angle based on information on the correction amount of the transmission power stored in the correction amount storage means;
The tire information acquisition device according to claim 1, comprising: The detection unit is provided for each tire mounted on the vehicle,
The detection unit is
Identification information storage means in which identification information unique to itself is stored in advance;
Means for transmitting the identification information together with the detection result;
The correction amount storing means for storing the correction amount information when receiving the correction amount information of the transmission power together with the identification information of the self,
The monitoring unit is
The test signal emission instruction means having means for transmitting a test signal emission instruction including identification information of the detection unit to be tested to the detection unit;
With the reference level storage means for each mounting position of each tire in the vehicle,
An identification information storage means for storing the identification information of the detection unit in advance corresponding to the mounting position of the tire;
The correction amount calculation means includes means for calculating a correction amount of transmission power for each detection unit,
The tire information acquisition apparatus according to claim 3, wherein the correction amount setting means includes means for transmitting a correction amount of transmission power together with identification information of the detection unit for each detection unit. The tire information acquisition device according to claim 3 or 4, wherein the value of the reference transmission power is set to the value of the maximum transmission power of the transmission unit.

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