阅读说明：本技术 加速度检测装置 (Acceleration detection device ) 是由 藤井慧友 于 2018-11-30 设计创作，主要内容包括：本发明提供加速度检测装置,具备：电源；加速度传感器,对通过车轮的旋转产生的离心加速度进行检测；取得部,以预定的取得周期从加速度传感器取得检测值,从而在车轮每旋转固定角度时从加速度传感器取得检测值；旋转周期计算部,计算车轮的旋转周期；以及取得周期设定部,设定取得周期。取得周期设定部以通过旋转周期计算部计算的旋转周期越长,在车轮旋转一圈期间从加速度传感器取得检测值的次数越多的方式,设定取得周期。(The present invention provides an acceleration detection device, comprising: a power source; an acceleration sensor that detects a centrifugal acceleration generated by rotation of the wheel; an acquisition unit that acquires a detection value from the acceleration sensor at a predetermined acquisition cycle, and acquires the detection value from the acceleration sensor every time the wheel rotates by a fixed angle; a rotation period calculation unit that calculates a rotation period of the wheel; and an acquisition cycle setting unit that sets an acquisition cycle. The acquisition cycle setting unit sets the acquisition cycle such that the longer the rotation cycle calculated by the rotation cycle calculation unit, the more times the detection value is acquired from the acceleration sensor during one rotation of the wheel.)

1. An acceleration detection device is provided with:

a power source;

an acceleration sensor configured to detect a centrifugal acceleration generated by rotation of the wheel;

an acquisition unit configured to acquire a detection value from the acceleration sensor at a predetermined acquisition cycle, and acquire the detection value from the acceleration sensor every time the wheel rotates by a fixed angle;

a rotation period calculation unit configured to calculate a rotation period of the wheel; and

an acquisition cycle setting unit that sets the acquisition cycle,

wherein the content of the first and second substances,

the acquisition cycle setting unit is configured to set the acquisition cycle,

the acquisition period is set such that the longer the rotation period calculated by the rotation period calculation unit, the more times the detection value is acquired from the acceleration sensor during one rotation of the wheel.

2. The acceleration detection device according to claim 1,

the acceleration detection device further includes a specific angle detection unit configured to compare at least two of the detection values continuously acquired by the acquisition unit and detect that the acceleration detection device is positioned at a predetermined specific angle from a transition of an increase or a decrease in the detection values.

3. The acceleration detection device according to claim 2,

the specific angle detection unit is configured to detect the specific angle,

the acceleration detection device determines that the acceleration detection device has passed the lowermost position or the uppermost position of the wheel, based on whether the detected value increases or decreases, or whether the detected value increases or decreases.

4. The acceleration detection device according to claim 1,

the acceleration detection device is attached to the back surface of the tread portion of the tire,

the acceleration detection device further includes a ground contact determination unit configured to determine that a portion of the tread portion where the acceleration sensor is located is grounded when a detection value of the acceleration sensor becomes smaller than a ground contact determination threshold from a state in which the detection value is equal to or larger than the predetermined ground contact determination threshold.

Technical Field

The present invention relates to an acceleration detection device.

Background

As described in patent document 1, a tire condition monitoring device that monitors the condition of a tire includes: a transmitter provided at a wheel; and a receiver receiving the transmission data transmitted from the transmitter. A transmitter is provided with: an acceleration sensor that detects centrifugal acceleration generated by rotation of the wheel; and a control unit for acquiring a detection value from the acceleration sensor. The control unit acquires the detection value of the acceleration sensor a plurality of times during one rotation of the wheel. The control unit can recognize the wheel state from the detection value of the acceleration sensor. The wheel state is, for example, whether or not the rotation angle of the wheel is a specific angle or the wheel is rotating.

Disclosure of Invention

Problems to be solved by the invention

When the number of times the detection value is obtained from the acceleration sensor during one wheel rotation is small, the wheel state may not be accurately grasped. It is also conceivable to increase the number of times the detection value is obtained from the acceleration sensor during one rotation of the wheel. However, in this case, there is a problem that power consumption increases and the life of the power supply becomes short.

An object of the present invention is to provide an acceleration detection device capable of reducing power consumption.

Means for solving the problems

In order to solve the above problem, according to a first aspect of the present invention, there is provided an acceleration detection device including: a power source; an acceleration sensor configured to detect a centrifugal acceleration generated by rotation of the wheel; an acquisition unit configured to acquire a detection value from the acceleration sensor at a predetermined acquisition cycle, and acquire the detection value from the acceleration sensor every time the wheel rotates by a fixed angle; a rotation period calculation unit configured to calculate a rotation period of the wheel; and an acquisition cycle setting unit that sets the acquisition cycle. The acquisition cycle setting unit is configured to set the acquisition cycle such that the number of times the detected value is acquired from the acceleration sensor during one rotation of the wheel increases as the rotation cycle calculated by the rotation cycle calculating unit increases.

The acquisition unit acquires the detection value from the acceleration sensor a large number of times when the rotation cycle of the wheel is long, and acquires the detection value from the acceleration sensor a small number of times when the rotation cycle of the wheel is short. Therefore, the power consumption can be reduced compared to the case where the number of times the detection value is obtained from the acceleration sensor is constant regardless of the rotation cycle of the wheel. Further, when the rotation cycle is long, the number of times the detection value is acquired from the acceleration sensor increases, so that the acceleration detection device can accurately grasp the wheel state.

The acceleration detection device may further include a specific angle detection unit configured to compare at least two of the detection values continuously acquired by the acquisition unit and detect that the acceleration detection device is positioned at a predetermined specific angle from a transition of increase and decrease of the detection values.

This makes it possible to detect that the rotation angle of the wheel is a specific angle.

In the acceleration detection device, the specific angle detection unit may be configured to determine that the acceleration detection device has passed the lowermost position or the uppermost position of the wheel, based on a transition from an increase to a decrease or from a decrease to an increase in increase or decrease in the detected value.

This makes it possible to determine whether the acceleration detection device has passed the uppermost position or the lowermost position.

The acceleration detection device may be attached to the back surface of a tread portion of a tire, and the acceleration detection device may further include a ground contact determination unit configured to determine that a portion of the tread portion where the acceleration sensor is located is grounded when a detection value of the acceleration sensor becomes smaller than a threshold value for ground contact determination from a state in which the detection value is equal to or larger than a predetermined threshold value for ground contact determination.

This makes it possible to accurately determine that the portion of the tread portion of the tire where the acceleration sensor is located has come into contact with the ground.

Effects of the invention

According to the present invention, power consumption can be reduced.

Drawings

Fig. 1 is a schematic configuration diagram of a tire condition monitoring system.

Fig. 2 is a schematic configuration diagram of the rotation sensor unit.

Fig. 3 is a schematic configuration diagram of a transmitter.

Fig. 4 is a flowchart showing a process performed by the transmission control unit when performing specific angle transmission.

Fig. 5 is a diagram showing a relationship between the rotation period and the number of times of acquisition.

Fig. 6 is a flowchart showing the wheel position determination process by the reception control section.

Fig. 7 is a diagram showing an example of a pulse count value obtained when reception of transmission data transmitted from a transmitter mounted on the left front wheel is triggered.

Fig. 8 is a schematic view of a transmitter provided in a tread portion of a tire.

Detailed Description

An embodiment of the acceleration detection device will be described below.

As shown in fig. 1, tire condition monitoring system 30 is mounted on vehicle 10.

The vehicle 10 includes four wheels 11, each wheel 11 includes a rim (wheel)12 and a tire 13 mounted on the rim 12, and the explanation will be given with the front right wheel 11 FR, the front left wheel 11F L, the rear right wheel 11 RR, and the rear left wheel 11R L among the wheels 11.

The vehicle 10 includes an antilock brake system (hereinafter, referred to as ABS) 20. the ABS20 includes an ABS controller 25 and rotation sensor units 21 to 24 corresponding to the four wheels 11, respectively, the 1 st rotation sensor unit 21 corresponds to the left front wheel F L, the 2 nd rotation sensor unit 22 corresponds to the right front wheel FR., the 3 rd rotation sensor unit 23 corresponds to the left rear wheel R L, the 4 th rotation sensor unit 24 corresponds to the right rear wheel rr. the ABS controller 25 is constituted by a microcomputer or the like, and the rotation angle of each wheel 11 is obtained based on signals from the rotation sensor units 21 to 24.

As shown in fig. 2, each of the rotation sensor units 21 to 24 includes: a gear 26 that rotates integrally with the wheel 11; and a detector 27 disposed so as to face the outer peripheral surface of the gear 26. A plurality of gear teeth are provided at regular angular intervals on the outer peripheral surface of the gear 26. The number of teeth of the gear 26 is 48. The detector 27 detects pulses generated by the rotation of the gear 26. The ABS controller 25 is connected to the detectors 27 via a wire, and determines the rotation angle of each wheel 11 from the pulse count value, which is the detection value of each detector 27. In detail, the ABS controller 25 counts the rising and falling edges of the pulse generated at the detector 27. The ABS controller 25 calculates a pulse count value as a remainder of dividing the counted pulse count number by 96, which is the count number of pulses of one rotation of the gear 26. Further, by dividing the number of pulses generated at the detector 27 during one rotation of the wheel 11 by 360 degrees, it is also possible to grasp that the gear 26 rotates by several degrees for each pulse count value. This enables the rotation angle of the wheel 11 to be obtained from the pulse count value. The pulse count value is 0 to 95.

Next, the tire condition monitoring system 30 will be explained.

As shown in fig. 1, tire condition monitoring system 30 includes: transmitters 31 mounted on the four wheels 11, respectively; and a receiver 50 provided at the vehicle 10. The transmitter 31 is mounted on the wheel 11 so as to be disposed in the inner space of the tire 13. As the transmitter 31, a transmitter fixed to a tire valve or a transmitter fixed to the rim 12 or the tire 13 is used. The transmitter 31 detects the state of the corresponding tire 13, and wirelessly transmits transmission data including information of the detected tire 13 to the receiver 50. Tire condition monitoring system 30 receives the transmission data transmitted from transmitter 31 via receiver 50, and monitors the condition of tire 13.

As shown in fig. 3, each transmitter 31 includes a pressure sensor 32, a temperature sensor 33, an acceleration sensor 34, a transmission control unit 35, a transmission circuit 36, a battery 37, and a transmission antenna 39. The transmitter 31 operates by the power supplied from the battery 37, and the transmission control unit 35 collectively controls the operation of the transmitter 31. The battery 37 serving as a power source of the transmitter 31 may be a primary battery, or may be a power storage device such as a secondary battery or a capacitor.

The pressure sensor 32 detects the air pressure of the corresponding tire 13. The temperature sensor 33 detects the temperature in the corresponding tire 13.

The acceleration sensor 34 is equipped to be able to detect centrifugal acceleration. The acceleration sensor 34 includes a detection axis, and detects acceleration in a direction in which the detection axis faces. The acceleration sensor 34 is attached to the wheel 11 so that the detection axis is oriented in the vertical direction when the transmitter 31 is located at the lowermost position of the wheel 11. The acceleration sensor 34 may be an acceleration sensor 34 of one axis or an acceleration sensor 34 of multiple axes as long as it can detect at least the centrifugal acceleration.

The transmission control unit 35 is constituted by a microcomputer or the like including a CPU35a and a storage unit 35b constituted by a RAM, a ROM, or the like. The transmission control unit 35 has a timer function. The timing function is implemented, for example, by a timer or a counter. The transmission control unit 35 may include dedicated hardware (application specific integrated circuit: ASIC) for executing at least a part of various processes. That is, the transmission control unit 35 may be configured as 1) one or more processors operating according to a computer program (software), 2) one or more dedicated hardware circuits such as an ASIC, or 3) a circuit (circuit) including a combination of these circuits. The processor includes a CPU and memories such as RAM and ROM. The memory stores program codes or instructions configured to cause the CPU to execute processing. Memory, i.e., computer-readable media, includes all available media that can be accessed by a general purpose or special purpose computer.

For convenience of explanation, the ID code of the transmitter 31 mounted on the front left wheel F L is expressed as F L ID, the ID code of the transmitter 31 mounted on the front right wheel FR is expressed as FRID, the ID code of the transmitter 31 mounted on the rear left wheel R L is expressed as R L ID, and the ID code of the transmitter 31 mounted on the rear right wheel RR is expressed as rrid, and the storage unit 35b stores various programs for controlling the transmitter 31.

The transmission control unit 35 generates transmission data and outputs the generated transmission data to the transmission circuit 36. The transmission data is digital data and is a string of binary data. The transmission circuit 36 modulates transmission data. The modulated transmission data is transmitted as a radio signal from the transmission antenna 39. The wireless signal refers to a signal containing transmission data. The radio signal is a signal in an RF band such as 315MHz band or 434MHz band.

The transmitter 31 is capable of general transmission for transmitting transmission data regardless of the rotation angle of the wheel 11 and specific angle transmission for transmitting transmission data when the rotation angle of the wheel 11 becomes a predetermined specific angle.

In the normal transmission, transmission data is transmitted from the transmitter 31 at predetermined intervals. The predetermined interval is, for example, ten seconds to several tens of seconds.

The specific angle transmission is performed, for example, when the vehicle 10 is continuously stopped for a predetermined time or more. The predetermined time is set to be longer than the time required for changing the position of the wheel 11 such as Tire rotation (Tire rotation) or the time required for replacing the wheel 11. The predetermined time is, for example, several tens of minutes to several hours.

Whether the vehicle 10 is running can be determined from the acceleration detected by the acceleration sensor 34. As the vehicle speed becomes faster, the centrifugal acceleration acting on the acceleration sensor 34 becomes larger. The transmission control unit 35 determines that the vehicle 10 is traveling if the acceleration detected by the acceleration sensor 34 is equal to or greater than the traveling determination threshold value. On the other hand, if the acceleration detected by the acceleration sensor 34 is smaller than the threshold value for travel determination, the transmission control unit 35 determines that the vehicle 10 is stopped. The travel determination threshold value is set to a value larger than the acceleration detected by the acceleration sensor 34 when the vehicle 10 is stopped, taking into account a tolerance and the like.

At the time of the specific angle transmission, when it is detected that the rotation angle of the wheel 11 is a predetermined specific angle, the transmission data is transmitted from the transmitter 31. To describe in detail, the transmission control unit 35 transmits the transmission data from the transmitter 31 when a predetermined time (for example, ten seconds to several tens of seconds) has elapsed since the last transmission of the transmission data and a specific angle is detected.

The control performed by the transmission control unit 35 when performing specific angle transmission will be described.

As shown in fig. 4, in step S1, the transmission control unit 35 acquires the detection value of the acceleration sensor 34. The transmission control unit 35 functions as an acquisition unit. Next, in step S2, the transmission control unit 35 calculates the rotation period [ sec ] of the wheel 11. To explain in detail, the transmission control unit 35 calculates the rotation period of the wheel 11 using the following expression (1).

[ formula 1 ]

Here, S is a rotation period [ sec ] of the wheel 11, G is a detection value [ G ] of the acceleration sensor 34, and R is a radius [ mm ] of the rim 12. The radius of the rim 12 is stored in the storage portion 35 b. The transmission control unit 35 functions as a rotation period calculation unit.

Next, in step S3, the transmission control unit 35 determines whether or not the rotation period S is equal to or greater than a threshold value. The threshold is used to determine whether the vehicle speed is low or high. The rotation period has a correlation with the vehicle speed, and the faster the vehicle speed, the shorter the rotation period. As the threshold value, for example, a value corresponding to a vehicle speed of 70[ km/h ] is set.

When the rotation period is equal to or greater than the threshold value, the transmission control unit 35 performs the process of step S4. When the rotation period is less than the threshold value, the transmission control unit 35 performs the process of step S5. In step S4, the transmission control unit 35 sets the acquisition count to 20. In step S5, the transmission control unit 35 sets the acquisition count to 10. The number of times of acquisition is the number of times of acquisition of the detection value from the acceleration sensor 34 during one rotation of the wheel 11. Therefore, it can be said that the transmission control unit 35 increases the number of times the detection value is acquired from the acceleration sensor 34 during one rotation of the wheel 11 as the rotation period calculated by equation (1) increases.

The number of times of acquisition set according to the rotation period preferably varies by an integral multiple. In the present embodiment, since the two types of acquisition count are set according to the rotation period, 10 times or 20 times 2 times the 10 times are set as the acquisition count. In the case where the number of acquisition times of the three methods is set according to the rotation period, the number of acquisition times is preferably set to 10, 20, or 30.

Next, in step S6, the transmission control unit 35 calculates an acquisition cycle, which is a cycle for acquiring the detection value from the acceleration sensor 34, from the set acquisition count. The acquisition cycle is set so that the detection values of the set acquisition times can be acquired during one rotation of the wheel 11. The acquisition period can be calculated by dividing the acquisition count by the rotation period. The transmission control unit 35 functions as an acquisition cycle setting unit.

Next, in step S7, the transmission control unit 35 detects that the rotation angle of the wheel 11 is a specific angle. First, the transmission control unit 35 acquires the detection value from the acceleration sensor 34 at the calculated acquisition cycle.

As shown in fig. 5, although the gravitational acceleration always acts in the vertical direction, the detection axis of the acceleration sensor 34 changes direction together with the rotation of the wheel 11, and therefore the gravitational acceleration detected by the acceleration sensor 34 varies depending on the rotation angle of the wheel 11. Specifically, the detection value of the acceleration sensor 34 changes in a sine wave around the centrifugal acceleration. In the present embodiment, the detected value of the centrifugal acceleration +1[ G ] is obtained when the acceleration sensor 34 is located at the lowermost position of the wheel 11, and the detected value of the centrifugal acceleration-1 [ G ] is obtained when the acceleration sensor 34 is located at the uppermost position of the wheel 11. For convenience of explanation, the origin of the rotation angle of the wheel 11 is set to 0 ° as the angle when the transmitter 31 is located at the forefront position of the wheel 11, the rotation angle of the wheel 11 when the transmitter 31 is located at the lowermost position of the wheel 11 is set to 90 °, the rotation angle of the wheel 11 when the transmitter 31 is located at the rearmost position of the wheel 11 is set to 180 °, and the rotation angle when the transmitter 31 is located at the uppermost position of the wheel 11 is set to 270 °. The uppermost position is the uppermost side of the wheel 11 in the vertical direction, and the lowermost position is the lowermost side of the wheel 11 in the vertical direction.

When the detection value is acquired from the acceleration sensor 34 in the acquisition cycle, if the acquisition count is 10 times, the detection value is acquired every time the wheel 11 rotates by 36 °. If the number of times of acquisition is 20, the detection value is acquired every time the wheel 11 rotates by 18 °. The detection value is acquired at a fixed angle interval according to the acquisition frequency. Therefore, the angle at which the detection value is acquired becomes a fixed angle in each acquisition count. For example, if the number of times of acquisition is 10, the detection values are acquired at fixed angles of 36 ° such as 0 °, 36 °, and 72 ° …, and if the number of times of acquisition is 20, the detection values are acquired at fixed angles of 18 ° such as 0 °, 18 °, and 36 ° ….

Acquisition points P1 to P10 in fig. 5 schematically show the times when the detection values were acquired 10 times. As long as the vehicle 10 does not suddenly accelerate or stops, it is rare that the vehicle speed greatly changes during one rotation of the wheel 11, and it can be said that the change in the detected value of the wheel 11 during one rotation is caused by the change in the position of the acceleration sensor 34. In other words, the rotation angle of the wheel 11 can be grasped from the change in the detection value of the acceleration sensor 34.

The rotation angle of the wheel 11 when the detection values are acquired at the acquisition points P1 to P10 fluctuates within a range of 1/2 in which the number of times of acquisition is increased or decreased by a value obtained by dividing 360 °. Therefore, if the number of acquisitions is 10, the rotation angle of the wheel 11 at the time of acquiring the detection values at the respective acquisition points P1 to P10 fluctuates within a range of ± 18 °. For example, when the rotation angle at which the detection value is acquired at the acquisition point P2 is made 36 °, the acquisition point P2 fluctuates within the range of 36 ° ± 18 °. The fixed angle described above allows for this error.

When the detection values acquired at the acquisition points P1 to P10 are compared with the detection values acquired at the acquisition points P1 to P10 immediately before the acquisition points P1 to P10, there are acquisition points P1 to P10 at which the detection values change from increasing to decreasing and acquisition points P1 to P10 at which the detection values change from decreasing to increasing. The + in fig. 5 indicates an increase and the-indicates a decrease. In the present embodiment, since the position where the acceleration due to gravity is detected to be the maximum is the position where the acceleration sensor 34 is located at the lowermost position of the wheel 11, when the acceleration sensor 34 passes the lowermost position of the wheel 11, the detection value is changed from increasing to decreasing. On the other hand, when the acceleration sensor 34 passes through the uppermost position of the wheel 11, the detection value is switched from decreasing to increasing. Therefore, the position of the acceleration sensor 34 can be grasped from the transition of increase and decrease of the detection value.

As can be understood from fig. 5, when the number of acquisition times is 20, the detection values are acquired at acquisition points P1 to P20. The detection values of the half number of acquisition points P1 to P10 out of the acquisition points P1 to P20 are acquired at the same rotation angle as the acquisition points P1 to P10 when the number of acquisition times is 10. When the number of times of acquisition is 20, the rotation angle of the wheel 11 at the time of acquiring the detection values at the acquisition points P1 to P20 fluctuates within a range of ± 9 °. For example, the rotation angle of the wheel 11 when the detection value is acquired at the acquisition point P2 is in the range of 36 ° ± 9 °. The acquisition points P11 to P20 are intermediate angles between two adjacent acquisition points of the acquisition points P1 to P10, respectively.

The transmission control unit 35 switches from increasing to decreasing in accordance with a transition between increase and decrease of at least two detection values obtained continuously, and detects that the transmitter 31 is positioned at a specific angle. When the number of times of acquisition is 10, the transmission control unit 35 determines that the transmitter 31 is positioned at the specific angle when the detected value decreases again after the transition of increase and decrease of the detected value changes from increase to decrease. That is, the transmission control unit 35 determines that the transmitter 31 is positioned at the specific angle when the transitions of increase and decrease of the detection value are arranged in the order of increase → decrease.

When the number of times of acquisition is 20, the transmission control unit 35 determines that the transmitter 31 is positioned at the specific angle when transitions of increase and decrease of the detection value are arranged in the order of increase → decrease. The specific angle in the present embodiment is 144 °. Since the specific angle varies depending on the number of acquisitions, the specific angle is 144 ° ± 18 ° if the number of acquisitions is 10, and 144 ° ± 9 ° if the number of acquisitions is 20. The transmission control unit 35 can determine that the transmitter 31 has passed the lowermost position of the wheel 11 by detecting the specific angle from the increase to the decrease in the transition of the increase or decrease in the detection value. The transmission control unit 35 functions as a specific angle detection unit.

As shown in fig. 4, next, in step S8, the transmission control unit 35 transmits the transmission data. Thereby, the transmission data is transmitted at a specific angle.

Instead of expression (1), the transmission control unit 35 may calculate the rotation period using an expression in which the numerator of expression (1) is obtained from the table. The storage unit of the transmission control unit 35 stores a table in which the value of the numerator of the expression (1) is associated with the radius R of the rim 12. When there is a difference between the set acquisition count and the count of detection values actually acquired during one rotation of the wheel 11, the transmission control unit 35 determines that there is an error in the calculated rotation period. Then, the transmission control unit 35 changes the value of the numerator of expression (1). When the set acquisition count matches the actual acquisition count, the transmission control unit 35 determines that the calculated rotation period is correct and adopts the value of the numerator. That is, even when the storage unit 35b does not store the radius R of the rim 12, the rotation period can be calculated.

As described above, the transmission control unit 35 functions as an acquisition unit, a rotation cycle calculation unit, an acquisition cycle setting unit, and a specific angle detection unit by executing predetermined programs. Therefore, the acceleration detection device 40 is configured by the battery 37 serving as a power source, the acceleration sensor 34, and the transmission control unit 35. The transmitter 31 includes the acceleration detection device 40, and the position of the transmitter 31 can be said to be the same as the position of the acceleration detection device 40.

Next, the receiver 50 will be explained.

As shown in fig. 1, the receiver 50 includes a reception control unit 51, a reception circuit 52, and a reception antenna 56. A display 57 mounted on the vehicle 10 is connected to the reception control unit 51. The reception control unit 51 is constituted by a microcomputer or the like including a reception CPU54 and a reception storage unit 55 constituted by a ROM, a RAM, or the like. The reception control unit 51 has a timer function. The timing function is implemented, for example, by a timer or a counter. The reception control unit 51 may include dedicated hardware (application specific integrated circuit: ASIC) for executing at least a part of various processes. That is, the reception control unit 51 may be configured as 1) one or more processors operating according to a computer program (software), 2) one or more dedicated hardware circuits such as an ASIC, or 3) a circuit (circuit) including a combination of these circuits. The processor includes a CPU and memories such as RAM and ROM. The memory stores program codes or instructions configured to cause the CPU to execute processing. Memory, i.e., computer-readable media, includes all available media that can be accessed by a general purpose or special purpose computer.

The reception circuit 52 demodulates the radio signal received from each transmitter 31 via the reception antenna 56, and outputs the transmission data from the transmitter 31 to the reception control unit 51.

The reception control unit 51 grasps the pressure in the tire 13 and the temperature in the tire 13 as the state of the tire 13 based on the transmission data output from the reception circuit 52. When an abnormality occurs in the tire 13, the reception control unit 51 displays a notification on the display 57.

The reception storage section 55 stores ID codes of the transmitters 31 mounted on the four wheels 11, respectively. Thereby, the transmitter 31 is associated with the receiver 50.

Here, it is sometimes desirable to determine which tire 13 of the four wheels 11 the received transmission data relates to. For example, there are cases where it is desired to display on the display 57 which tire 13 has generated a pressure abnormality generated in one tire 13 among the four wheels 11, or cases where it is desired to display on the display 57 the pressure of the tire 13 corresponding to each position of the wheel 11. In the case described above, it is necessary to determine which wheel 11 the received transmission data relates to. In other words, the reception control section 51 needs to perform association of the ID code of each transmitter 31 with the position of the wheel 11.

Hereinafter, a wheel position determination process of determining which of the four wheels 11 each transmitter 31 is mounted on will be described. The wheel position determination process is performed, for example, when the vehicle 10 is started by a start switch that switches a start state and a stop state of the vehicle 10. The starting state of the vehicle 10 refers to a state in which the vehicle 10 can be caused to run by operation of an accelerator pedal. The stopped state of the vehicle 10 refers to a state in which the vehicle 10 does not run even if the accelerator pedal is operated.

As shown in fig. 6, in step S11, the reception control unit 51 receives the transmission data. Next, the reception control unit 51 obtains the vehicle speed from the ABS controller 25. Next, in step S13, the reception control unit 51 acquires the pulse count values of the rotation sensor units 21 to 24 from the ABS controller 25 when the transmission data is received. The processing in step S12 and step S13 is performed when the transmission data is acquired.

Next, in step S14, the reception control section 51 performs position determination that determines which of the four wheels 11 each transmitter 31 is mounted on. The position determination is performed by acquiring and collecting the pulse count value every time transmission data is received, when reception of the transmission data is triggered. The number of rotations of each wheel 11 differs by the influence of a differential or the like. Therefore, the relative position of the transmitter 31 mounted on the wheel 11 changes with the travel of the vehicle 10. On the other hand, when the transmitter 31 transmits transmission data at a specific angle, the rotation angle of each of the four wheels 11 is synchronized with the rotation angle at which the transmission data is transmitted from any one of the four transmitters 31. Therefore, when the transmitter 31 transmits the transmission data at a specific angle and the pulse count value is acquired when the transmission data is received, the rotation sensor units 21 to 24 corresponding to the transmitters 31 have a small variation in the pulse count value. The reception control unit 51 determines which of the four wheels 11 each transmitter 31 is mounted on, from the deviation of the pulse count value collected each time transmission data is acquired.

When the collected plurality of pulse count values converge within a predetermined range, the reception control section 51 associates the rotation sensor unit that has detected the pulse count value with the transmitter 31. The predetermined range is a range set in consideration of variations in pulse count values, and is used for determining the rotation sensor units 21 to 24 having a small variation in pulse count values. The reception control unit 51 changes the predetermined range according to the vehicle speed. The reception control unit 51 increases the predetermined range in the case where the vehicle speed is equal to or greater than the speed threshold value, as compared to the case where the vehicle speed is less than the speed threshold value. The speed threshold value is a value corresponding to a threshold value set as a rotation period. In the present embodiment, the threshold value set as the rotation period corresponds to a vehicle speed of 70[ km/h ], and therefore the speed threshold value is 70[ km/h ]. The difference between the predetermined range when the vehicle speed is less than the speed threshold value and the predetermined range when the vehicle speed is equal to or greater than the speed threshold value is, for example, a pulse count value + a redundancy amount corresponding to 18 °. That is, the predetermined range is set in consideration of the deviation of the specific angle corresponding to the number of times of acquisition.

In the example shown in fig. 7, the deviation of the pulse count value detected by the 1 st rotation sensor unit 21 corresponding to the front left wheel F L is the least, and therefore, the transmitter 31 of the F L ID is able to be fitted to the front left wheel F L, in the example shown in fig. 7, the pulse count value detected by the 1 st rotation sensor unit 21 when the number of acquisitions is 10 is indicated by ○ (white circle), and the pulse count value detected by the 1 st rotation sensor unit 21 when the number of acquisitions is 20 is indicated by ● (black circle), since the deviation of the specific angle of the transmission data is small, it is known that the deviation of the pulse count value is also small, the reception control section 51 determines which of the four wheels 11 the transmitter 31 of the FFID, R L ID, and the RRID is fitted to which of the four wheels 11, and the reception control section 51 stores the four ID codes in the reception storage section 55 in association with the positions of the wheels 11, and repeats the processing of steps S63 to S14 every time the reception control section determines the positions of the wheels 11, and when the reception control section determines the positions of the four transmitter codes by associating the reception control section 51.

The operation of the present embodiment will be described.

The transmission control unit 35 detects a specific angle from the detection value of the acceleration sensor 34. The transmission control unit 35 intermittently acquires the detection value of the acceleration sensor 34 in order to reduce the power consumption of the battery 37. Thus, the transmission control unit 35 has a time when the detection value cannot be acquired.

In the present embodiment, when the specific angle transmission is performed and the rotation cycle is smaller than the threshold value, the number of times the detection value is acquired during one rotation of the wheel 11 is increased. The number of times of acquisition of the detection value is increased only when the specific condition is satisfied, thereby improving the detection accuracy of the specific angle. In the present embodiment, the number of times of acquisition is changed from 10 to 20, thereby reducing the deviation of the specific angle from ± 18 ° to ± 9 °. As a result, the reception controller 51 can narrow the predetermined range for position determination. Thus, the number of pulse counts included in the predetermined range becomes small, and the time required for determining the position of which wheel 11 the transmitter 31 is mounted on can be shortened.

In addition, it is also conceivable to always increase the number of acquisitions regardless of the rotation period. However, in this case, there is a problem that the transmission at the specific angle cannot be performed during high-speed traveling. When the number of times of acquisition is increased, the acquisition cycle becomes shorter. Further, since the acquisition cycle becomes shorter than the vehicle speed, the acquisition cycle becomes too short when the number of acquisitions is large during high-speed traveling. The transmission control unit 35 needs a processing time for performing various processes such as comparison with the previous detection value when obtaining the detection value from the acceleration sensor 34. If the acquisition cycle is shorter than the processing time, the detection value is acquired regardless of the fact that the processing is not completed, and the processing cannot be performed correctly. At this time, specific angle transmission cannot be performed. That is, the acquisition cycle needs to be longer than the processing time + redundancy, and the number of acquisitions cannot be increased regardless of the rotation cycle. Further, if the number of times of acquisition is increased regardless of the rotation cycle, power consumption increases, and the life of the battery 37 becomes short.

In contrast, in the present embodiment, by increasing the number of acquisitions when the rotation cycle is smaller than the threshold value, it is possible to shorten the time required for determining which wheel 11 each transmitter 31 is attached to when the rotation cycle is smaller than the threshold value. In particular, as the threshold value to be set as the rotation period, a value in consideration of the common region in each country is set, thereby obtaining a significant effect.

For example, in Japan, except for an expressway, the frequency of traveling at a vehicle speed of 70[ km/h ] or less is dominant. Therefore, by setting 70[ km/h ] as the threshold value set as the rotation cycle, the effect of the acceleration detection device 40 of the present embodiment can be enjoyed in most of the time periods in which the vehicle 10 is used.

The effects of the present embodiment will be described.

(1) The transmission control unit 35 increases the number of times the detection value is obtained from the acceleration sensor 34 when the rotation cycle of the wheel 11 is long, and decreases the number of times the detection value is obtained from the acceleration sensor 34 when the rotation cycle of the wheel 11 is short. Therefore, compared to the case where the number of times the detection value is obtained from the acceleration sensor 34 is constant regardless of the rotation cycle of the wheel 11, it is possible to reduce the power consumption. Further, since the number of times the detection value is acquired from the acceleration sensor 34 increases when the rotation cycle is long, the transmission control unit 35 can accurately grasp the state of the wheel 11.

(2) The transition detection transmitter 31, from which the transmission control unit 35 can increase or decrease the detection value, is at a specific angle. The transmission control unit 35 can transmit transmission data at a specific angle, and thus can cause the receiver to determine to which wheel 11 each transmitter 31 is attached.

(3) The transmission control unit 35 determines that the transmitter 31 is at the specific angle when the transition of increase and decrease of the detection value changes from increase to decrease. Therefore, it can be determined that the transmitter 31 has passed the lowermost position.

The embodiment can be modified as described below. The embodiments and the following modifications can be combined with each other within a range not technically contradictory to the present invention.

The transmission control unit 35 may determine whether or not a portion of the tire 13 where the acceleration sensor 34 is located is in contact with the ground, based on the detection value of the acceleration sensor 34. That is, instead of detecting the specific angle as in the embodiment, the acceleration detection device 40 may be used to determine the grounding. At this time, as shown in fig. 8, the transmitter 31 is provided on the back surface 15 of the tread portion 14 of the tire 13, that is, the surface opposite to the surface contacting the road surface. A portion of the tread portion 14 of the tire 13 where the acceleration sensor 34 is located is referred to as a sensor arrangement portion.

When the sensor arrangement portion of the tire 13 contacts the ground during running of the vehicle 10, the portion of the tread portion 14 contacting the road surface is pressed, and a force in the direction opposite to the centrifugal acceleration acts on the acceleration sensor 34. Therefore, the detection value of the acceleration sensor 34 decreases at the time when the sensor arrangement portion comes into contact with the road surface. Therefore, when the detection value of acceleration sensor 34 becomes smaller than the ground contact determination threshold value from a state equal to or larger than the predetermined ground contact determination threshold value, transmission control unit 35 can determine that the sensor arrangement portion of tread portion 14 of tire 13 has been grounded. The threshold value for ground fault determination is a value larger than the detection value of the acceleration sensor 34 while the vehicle 10 is stopped. The transmission control unit 35 functions as a ground fault determination unit. In addition, the determination of the grounding of the sensor arrangement portion may be performed by the amount of change in the detection value instead of the determination using the threshold value for grounding determination. When the sensor arrangement portion is grounded, the centrifugal acceleration is canceled out, and the detection value is greatly reduced. Therefore, it may be determined that the sensor arrangement portion is grounded when the amount of change in the detection value is equal to or greater than a predetermined value.

The acceleration detection device 40 is used, for example, in the transmitter 31 for detecting the road surface condition. In the transmitter 31, the road surface condition is estimated from the detection result of the sensor obtained at the time when the sensor arrangement portion of the tire 13 is in contact with the ground. Therefore, detection of the sensor arrangement portion ground is important. The time for grounding the sensor arrangement portion is short, and the problem arises that the grounding of the sensor arrangement portion cannot be detected as the number of acquisition times is small. On the other hand, the acceleration detection device 40 obtains a larger number of times according to the rotation cycle of the wheel 11. Therefore, it is possible to accurately grasp that the sensor arrangement portion is in contact with the ground, in other words, that the rotation angle of the wheel 11 is the angle at which the sensor arrangement portion is in contact with the ground.

The transmission control unit 35 may determine that the transmitter 31 is at the specific angle by switching from decreasing to increasing in accordance with a transition of increase and decrease in the detection value. At this time, the transmission control unit 35 can determine that the transmitter 31 has passed the uppermost position of the wheel 11.

The specific angle at which the transmission control unit 35 transmits the transmission data may be changed. In this case, the specific angle may be changed by changing the transmission data at the time when the increase or decrease of the detection value changes.

A plurality of specific angles may be set.

The number of times of acquisition may be changed as appropriate.

The number of acquisitions may be increased linearly as the rotation period becomes longer without using a threshold.

The acceleration sensor 34 may be provided in any manner as long as it can detect centrifugal acceleration.

As the power source of the transmitter 31, various power generating elements may be used. Even when a member capable of charging and generating electricity is used as a power source, the available power is limited. Therefore, it is preferable to reduce power consumption caused by transmission of transmission data, and to transmit the transmission data without including data indicating angle information, thereby making it possible to effectively use limited power.

In each embodiment, the vehicle 10 may include a plurality of wheels 11, and may be a two-wheeled vehicle, for example.

The receiver 50 may be a portable terminal or the like held by a passenger of the vehicle 10.

Description of the reference numerals

11 … wheels, 13 … tires, 14 … tread portion, 15 … back face, 34 … acceleration sensor, 35 … transmission control portion (acquisition portion, rotation period calculation portion, acquisition period setting portion and specific angle detection portion), 37 … battery (power source).