JP2007010427A - Tire pressure monitoring system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tire air pressure monitoring system wherein a communication success probability is not lowered even at high speed. <P>SOLUTION: A transmitter transmits the second packet P2 at an interval T1 from transmission start of the first packet P1, then starts transmission of the first packet P1 at an interval T2 from transmission start of the second packet P2, and furthermore transmits the second packet P2 at the interval T1. The transmission timing is repeated regardless of rotational speed of the tire during rotation of the tire. The first packet P1 has a packet format wherein a reception success probability is heightened at a low-speed rotation time of the tire, and the second packet P2 has a packet format wherein the reception success probability is heightened at a high-speed rotation time of the tire. The intervals T1, T2 are determined in consideration of the time required for processing a received packet. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a tire pressure monitoring system, and more particularly to a tire pressure monitoring system that transmits tire pressure data from a transmitter installed in a tire and can be monitored in a vehicle via a receiver installed in a vehicle body. .

  In recent years, a tire pressure monitoring system has been proposed in which tire pressure data is transmitted from a transmitter installed in a tire and can be monitored in a vehicle via a receiver installed in a vehicle body. However, the proposed conventional tire pressure monitoring system has a problem that the wireless communication performance at the time of high speed (for example, about 100 km / h) operation is not sufficient. This is because the characteristics of wireless output transmitted from within the tire are not constant, and there are points (hereinafter referred to as “NULL points”) that cannot be communicated in certain areas.

  As a conventional method for avoiding the influence of this null point, a method of receiving transmitted data with a plurality of antennas has been attempted (see Patent Document 1). However, this method cannot be used when the place where the receiving antenna is attached is restricted by the vehicle, and even if it is not restricted by the vehicle, there is a problem that increasing the number of receiving antennas leads to an increase in cost.

  In addition, as another conventional method for avoiding the influence of the null point, a short packet is continuously transmitted from the transmitter installed in the tire and the number of times is increased to improve the communication success probability between the transmitter and the receiver. Attempts have also been made. By the way, most transmitters installed in tires are driven by batteries, and considering the power consumption, there is a situation in which the number of times the transmitter performs radio transmission cannot be increased unnecessarily.

Further, as another conventional method for avoiding the influence of the null point, a method of transmitting at a plurality of communication baud rates, in that case, a method of attaching a speed sensor to the transmitter side and changing a transmission packet based on the vehicle speed ( However, there has been a problem that all of them are not practical because they lead to an increase in cost as compared with the case of only a single transmission packet.
JP 2001-56263 A JP 2003-182325 A

  Here, the reason why the communication success probability decreases at high speed (when the tire rotates at high speed) will be described. As shown in FIG. 1, a battery-driven transmitter 3 is attached to a wheel 2 in a tire 1, and a receiver 4 is attached to a part of a vehicle body (not shown) outside the tire 1. The receiver 4 is provided with an antenna 5. The antenna associated with the transmitter 3 is not shown. When the tire 1 is rotated, when data such as tire pressure measured by a sensor (not shown) is packetized by the transmitter 3 and transmitted from the transmitter 3, the packet data is received by the receiver 4 via the antenna 5. The The reception characteristics when received by the receiver 4 are as shown in the graph of FIG. 2, and as shown in FIG. 2, in the region where communication is not possible during one rotation of the tire 1 (NULL point), packets are received. Data cannot be received correctly.

  When packet data is transmitted from the transmitter 3, the higher the speed of the tire 1 is, the more cases where a null point is applied during packet transmission. As a result, the probability of successful wireless communication decreases. Although an example in which one null point exists has been described with reference to FIG. 2, the present invention is not limited to one point, and a plurality of points may exist depending on circumstances.

  In view of the above problems, an object of the present invention is to provide a tire pressure monitoring system in which the communication success probability does not decrease even at high speeds.

  The present invention relates to a tire pressure monitoring system in which measurement data relating to tire pressure is packetized and transmitted from a transmitter installed in a tire, is received by a receiver installed in a vehicle body, and is monitored in the vehicle. Comprises means for alternately transmitting the measurement data in first and second packets having different formats regardless of the rotational speed of the tire.

  According to the present invention, it is possible to improve the probability of successful communication without increasing power consumption and with the processing capability of the receiver being almost the same as the specification when receiving only one type of packet.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a configuration of a tire pressure monitoring system according to an embodiment of the present invention. In FIG. 1, a tire pressure monitoring system according to an embodiment of the present invention includes a battery-driven transmitter 3 attached to a wheel 2 in a tire 1 and a receiver on a part of a vehicle body (not shown) outside the tire 1. 4 is attached, and tire pressure data measured by a sensor (not shown) is transmitted from the transmitter 3 in a packet format. The transmitted packet data is received by the receiver 4 via the antenna 5. Packet data received by the receiver 4 is sent to and monitored by a control device (not shown) installed in the vehicle. In the tire pressure monitoring system configured as described above, the transmitter 3 according to the embodiment of the present invention transmits packet data at the transmission timing shown in FIG. That is, in FIG. 3, the transmitter 3 according to the embodiment of the present invention transmits the second packet P2 at an interval T1 after starting transmission of the first packet P1. Then, the transmission of the first packet P1 is started at an interval T2 after the transmission of the second packet P2 is started, and the second packet P2 is transmitted at an interval T1. While the tire is rotating, this transmission timing is repeated regardless of the rotation speed of the tire. The first packet P1 has a packet format that increases the reception success probability when the tire rotates at a low speed, and the second packet P2 has a packet format that increases the reception success probability when the tire rotates at a high speed. The intervals T1 and T2 are determined in consideration of the time required for processing the received packet.

  As described above, the tire pressure monitoring system according to the present embodiment includes the first packet P1 having a high reception success probability when the tire rotates at a low speed and the second packet P2 having a high reception success probability when the tire rotates at a high speed. The transmission is alternately performed from the transmitter 3 at the transmission timing as shown in FIG. 3, and in this way, the communication success probability at the time of high-speed rotation of the tire without lowering the reception success probability at the time of low-speed rotation of the tire. Can be guaranteed.

  As shown in FIG. 1 and FIG. 2, a null point always exists while the tire 1 makes one revolution, and therefore the communication success probability decreases in a case where the null point is straddled during wireless communication. Therefore, when the tire 1 is rotating at a low speed, the wireless communication is terminated while the tire 1 does not pass the null point. Therefore, a packet P1 having a short frame length (see Table 1 below) is selected. On the other hand, when the tire 1 rotates at a high speed, the number of cases where a packet with a short frame length passes through the null point increases. Therefore, the packet P2 that is assumed to pass through the null point is transmitted. Therefore, as the packet P2, a packet that can be corrected if there is an error of several bits even if the frame length is somewhat longer is selected. In other words, even if the tire 1 rotates at a high speed, a packet having the ability to correct an error of a few bits even if the frame length is somewhat long so that the time to pass the null point is kept within a few bits (see Table 1 below Select). The packet P2 is preferably a frame having an error correction capability of N bits for each block.

  As described above, in the embodiment of the present invention, the packet P1 having a frame length as short as possible is transmitted as a packet suitable for low-speed traveling, while the packet P2 having a slightly longer frame length including error correction capability and redundant data is included. Transmits packet P2 at intervals of T1 after starting transmission of packet P1 as a packet suitable for high-speed driving, and alternately transmits packet P2, and at intervals T2 longer than T1 after transmission of packet P2 starts. Packet P1, then packet P2 and so on. Packets P1 and P2 are sent alternately. By repeating this, the communication success at high speed rotation of the tire is achieved without reducing the probability of successful reception at low speed rotation of the tire. Probability can be guaranteed. As a result, the tire pressure can be monitored without reducing the packet reception success probability even in the case where the tire rotation speed repeats from high speed → low speed → high speed. Note that the sending order of the packets P1 and P2 shown in FIG. 1 may be reversed.

Next, the reason why the communication success probability at the time of high speed rotation of the tire can be guaranteed without reducing the reception success probability at the time of low speed rotation of the tire will be described in detail.
[Definition]
Probability of successful packet reception A: Probability of completing communication without straddling the null point Probability of successful packet reception B: Probability of passing through the null point within an error correctable time Probability of successful communication: Transmitting the packet once Probability of successful communication sometimes Probability of successful system communication: Probability of successful communication with both or one when P1 and P2 are sent once

[a formula]
N [bit] / baud rate [bps] = N-bit communication disabled time [s] (Equation 1)
Tire external size [m] / speed [m / s] = time for one revolution of tire [s] ... (Formula 2)
Tire rotation time [s] x (Null angle not received [degrees] / 360 [degrees]) = Not received time [s]
... (Formula 3)
From the above, the packet reception success probability A is obtained by the following equation 4.
(1- (unavailable time [s] + frame length [s]) / time for one revolution of tire [s]) x 100
= Packet reception success probability A [%] (Formula 4)
The packet reception success probability B is divided into cases (1) to (3), and is obtained by the following equations 5 to 7.
(1) When reception is unavailable> (N + 1) bit communication unavailable time:
0 [%] = packet reception success probability B [%] ... (Formula 5)
(2) N bit communication unavailable time <reception unavailable time <(N + 1) bit communication unavailable time:
(1- (Reception unavailable time [s] -N bit communication unavailable time) / 1 bit communication unavailable time) x 100
= Packet reception success probability B [%] (Equation 6)
(3) When reception unavailable time <N bit communication unavailable time:
100 [%] = packet reception success probability B [%] (Equation 7)
From the above, the communication success probability is obtained as shown in Equation 8 below.
Packet reception success probability A + (1-packet reception success probability A) × packet reception success probability B
= Probability of communication success (Equation 8)
In addition, the system communication success probability is obtained as shown in Equation 9 below.
1- (1-P1 communication success probability) × (1-P2 communication success probability) = system communication success probability (Equation 9)
The results obtained from the above equations based on the following performance, specifications and parameters are displayed in a graph, and the effects brought about by the embodiments of the present invention will be described based on the results.

[Performance, specifications, parameters]
Tire outer size: The circumference of the tire surface is 2.6 [m].
Non-reception null angle: Width of non-reception angle = 3 [degrees], and there is one place in a circle.

  Note that the above performance, specifications and parameters are all reference values. Then, when the probability distribution is obtained in relation to the speed by the above formula based on these values, the relation between the speed and the packet reception success probability A is expressed as in the graph of FIG. 5 and the relationship between the speed and the communication success probability for each packet (packets P1, P2) are represented as in the graph of FIG. High communication success probability can be obtained by using packet P2 when P1 and tire rotate at high speed.

  In addition, as shown in FIG. 7, the system communication success probability is obtained as the sum of the packet P1 reception success probability and the packet P2 reception success probability shown in FIG. 4, so that a high communication success probability regardless of the tire rotation speed. Can be maintained.

  FIG. 8 shows the structure of the packet frame format according to the present invention in which the packet type is specified by the data type existing in the specific part of the packet, instead of specifying the packet type at the transmission timing shown in FIG. FIG. In FIG. 8, the first packet P1 according to the present invention is composed of frames including synchronization data, type 1, and data, and the second packet P2 according to the present invention is a frame including synchronization data, type 2, and data. It is configured. When the first and second packets configured as described above are transmitted from the transmitter 3, the receiver 4 decodes the data type existing in a predetermined portion of the received packet frame and receives the received packet. Can be easily distinguished whether it is the first packet P1 or the second packet P2.

  As described above, in another tire pressure monitoring system according to the embodiment of the present invention, the packet type is specified without decoding the transmission timing by decoding the data type existing in the specific part of the packet on the receiving side and specifying the packet type. Can be received. Needless to say, the receiver has a function of simultaneously monitoring two packets in order to identify the packet type by decoding the data type existing in the specific part of the packet on the receiving side.

  FIG. 9 is a schematic diagram showing the configuration of another tire pressure monitoring system according to the embodiment of the present invention. In this embodiment, as shown in FIG. 9, the vehicle speed by the speedometer 6 is input to the receiver 4. As shown in FIG. 6 of the embodiment of the present invention described above, when the vehicle speed is 150 [km / h] or less, the probability of successful reception of the first packet P1 is high, and when the vehicle speed is 150 [km / h] or more. Since the probability of successful reception of the second packet P2 is high, when the vehicle speed input by the speedometer 6 is 150 [km / h] or less, the vehicle speed input by the first packet P1 and the speedometer 6 is 150 [km. / h] By setting the receiver 4 in advance so as to receive the second packet P2, when compared with the system receiving only the first packet P1 and only the second packet P2, communication is performed. The probability of success can be improved.

  As described above, in another tire pressure monitoring system according to the embodiment of the present invention, by setting the receiver to transit to a mode in which a receiver receives a packet having a high communication success probability from the vehicle speed input, communication equivalent to that at low speed is performed. Quality can be maintained. Further, if the technique for discriminating the received packet type according to the type in the frame is used, it is possible to adopt a system configuration in which the speedometer 6 is removed.

It is a figure which shows the structure of the tire pressure monitoring system which concerns on embodiment of this invention. It is a figure which shows a mode that it becomes impossible to receive at a null point. It is a figure which shows the packet transmission timing in the tire pressure monitoring system which concerns on embodiment of this invention. It is a graph which shows the relationship between a speed and the packet reception success probability A defined by this invention. It is a graph which shows the relationship between a speed and the packet reception success probability B defined by this invention. It is a graph which shows the relationship between speed and the communication success probability for every packet defined by this invention. 5 is a graph showing the communication success probability for each packet shown in FIG. 4 and the system communication success probability defined by the present invention obtained by alternately transmitting both packets. It is a figure which shows the structure of the packet frame format which concerns on this invention. It is the schematic which shows the structure of the other tire pressure monitoring system which concerns on embodiment of this invention.

Explanation of symbols

1 Tire 2 Wheel 3 Transmitter 4 Receiver 5 Antenna 6 Speedometer

Claims (6)

In a tire pressure monitoring system that transmits measurement data related to tire pressure from a transmitter installed in a tire, packetizes it, receives it with a receiver installed on the vehicle body, and monitors it inside the vehicle,
The tire pressure monitoring system according to claim 1, wherein the transmitter includes means for alternately transmitting the measurement data in first and second packets having different formats regardless of the rotation speed of the tire.   The first packet has a packet format with a short frame length that increases the probability of successful reception when the tire rotates at a low speed, and the second packet has a frame length that increases the probability of successful reception when the tire rotates at a high speed. 2. The tire pressure monitoring system according to claim 1, wherein the tire pressure monitoring system has a packet format longer than one packet and having an error correction capability of several bits.   The tire pressure monitoring system according to claim 1, wherein the transmitter alternately defines the transmission order of the first and second packets in advance.   The tire pressure monitoring system according to claim 1, wherein an area indicating a data type is provided in a format of a packet transmitted by the transmitter, and the transmitter describes a data type in the type and transmits the data.   The tire pressure monitoring system according to any one of claims 1 to 4, wherein the receiver selects and receives an appropriate packet based on a speed parameter indicating a vehicle speed.   The tire pressure monitoring system according to claim 1, wherein the receiver has a function of simultaneously monitoring and receiving the first and second packets.