JP2012218682A - Wheel load value calculating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wheel load value calculating device capable of accurately calculating a value of a load applied to a tire based on the grounding area of the tire.SOLUTION: This wheel load value calculating device includes: sensor units 21a-21d for measuring pneumatic pressure of the tires Tia-Tid installed in wheels 20a-20d of a vehicle 1; piezoelectric elements 24a-24d for detecting a change in the circumferential direction and a change in the width direction of a tire load applied to the tires Tia-Tid when the vehicle 1 travels; and a control device 10 for calculating a tire load value. The control device 10 calculates the grounding area of the tires Tia-Tid based on the grounding length in the circumferential direction of the tires Tia-Tid and a grounding width in the width direction of the tires Tia-Tid, and also calculates the tire load value by using a correlation between the grounding area and the tire load value set with every pneumatic pressure of the tires based on a calculation value of the grounding area and a measured value of the tire pneumatic pressure.

Description

  The present invention relates to a wheel load value calculation device for calculating a load value applied to a tire mounted on a vehicle wheel.

A method of calculating (estimating) a value of a load applied to a wheel (wheel load) is widely known. For example, Patent Document 1 discloses a tire dynamic load radius, a tire slip ratio, a tire initial internal pressure, and a vehicle weight. A method of estimating the wheel load value (the tire wheel load value) from the above is described.
Patent Document 2 describes a method of calculating a wheel load value based on deformation of a tire on the wheel contact surface (length of the wheel contact surface).

JP 2010-76703 A JP 2010-66261 A

  The technique disclosed in Patent Document 1 is a technique for calculating (estimating) a wheel load value from a dynamic load radius of a tire, a slip ratio, and the like, and an error from an actual wheel load value is likely to occur.

Patent Document 2 discloses a technique for obtaining a wheel load based on deformation of the tire (the length of the contact surface).
However, the wheel load is highly correlated with the area of the ground contact surface of the tire, and the wheel load calculated based on the area of the tire ground contact surface is highly accurate, but the wheel load calculated based on the length of the ground contact surface is high. The accuracy of the load is lower than the wheel load calculated based on the area of the contact surface. That is, the wheel load calculated by the technique disclosed in Patent Document 2 tends to cause an error from the actual wheel load.

  Therefore, an object of the present invention is to provide a wheel load value calculation device that can accurately calculate the value of a load applied to a tire based on the contact area of the tire.

  In order to solve the above-mentioned problems, the present invention relates to a pneumatic pressure measuring means for measuring a pneumatic pressure of a tire mounted on a wheel provided in a vehicle, and a change in a circumferential direction of a load applied to the tire when the vehicle travels. A wheel load value calculating device includes first detecting means for detecting, second detecting means for detecting a change in the width direction of the load, and a control device for calculating the value of the load. The control device is configured to control the tire based on a ground contact length in the circumferential direction of the tire calculated from a change in the circumferential direction of the load and a contact width in the width direction of the tire calculated from a change in the width direction of the load. The contact area is calculated, and further, the correlation between the contact area and the load value set for each air pressure based on the calculated value of the contact area and the measured value of the tire air pressure measured by the air pressure measuring means. The load value is calculated using the relationship.

  According to this invention, based on the change in the circumferential direction of the tire load detected by the first detection means and the change in the width direction of the tire load detected by the second detection means, the contact length in the circumferential direction of the tire and the width direction of the tire are detected. The contact width can be calculated, and further, the contact area of the tire can be calculated from the contact length and the contact width. Based on the calculated value of the tire contact area and the measured value of the tire pressure, the value of the load applied to the tire using the correlation between the contact area set for each tire pressure and the value of the load applied to the tire. Can be calculated. Thus, the load calculated based on the tire contact area and the tire air pressure is highly accurate. Therefore, the value of the load applied to the tire can be calculated with high accuracy.

Further, according to the present invention, the first detection means and the second detection means are attached to the inner peripheral surface of the tire, and are deformed along with the deformation of the tire at a boundary where the tire is deformed flat on the contact surface. The piezoelectric element generates a voltage as a boundary voltage as a detection value.
Therefore, the present invention can be configured such that the tire contact area can be calculated only by providing the first detection means and the second detection means with piezoelectric elements attached to the inner peripheral surface of the tire.

Further, the present invention provides the detection values of the first detection means and the second detection means by the transmission means for transmitting the measurement value of the air pressure measurement means attached to the wheel to the control device provided in the vehicle body. It is transmitted to the control device.
Therefore, the present invention provides the measurement value of the air pressure measurement means without newly providing a device for transmitting the detection values of the first detection means and the second detection means attached to the tire to the control device provided in the vehicle body. The detection values of the first detection means and the second detection means can be transmitted to the control device using the transmission means for transmitting to the control device.

In addition, according to the present invention, when the load value calculated using the correlation based on the calculated value of the ground contact area and the measured value of the air pressure exceeds the maximum load capacity of the tire And an overload determination unit for determining an overload state of the tire.
Therefore, the present invention includes an overload determination unit that can accurately determine a tire overload state by using a load that is accurately calculated based on a calculated value of a tire contact area and a measured value of tire air pressure. be able to.

Further, according to the present invention, the control device includes a value of the load calculated using the correlation based on a calculated value of the contact area and a measured value of the air pressure, and a maximum load capacity of the tire. An overload determination unit that determines an overload state of the tire when the tire load factor calculated based on the tire exceeds a predetermined threshold value is provided.
Therefore, according to the present invention, the tire load factor can be calculated based on a load that is accurately calculated based on the calculated value of the contact area of the tire and the measured value of the tire air pressure. Furthermore, it is possible to provide an overload determination unit that can accurately determine the tire overload state by using the tire load factor.

Further, according to the present invention, the control device calculates a total vehicle weight of the vehicle from the load value calculated using the correlation based on the calculated value of the ground contact area and the measured value of the air pressure. An overload determination unit that determines an overload state of the vehicle when a value obtained by subtracting a preset vehicle weight from the calculated total vehicle weight exceeds a maximum load weight set in the vehicle. It is characterized by.
Therefore, the present invention provides an overload determination unit that can accurately determine an overload state of a vehicle using a load that is accurately calculated based on a calculated value of a tire contact area and a measured value of tire air pressure. Can be provided.

  ADVANTAGE OF THE INVENTION According to this invention, the wheel load value calculation apparatus which can calculate the value of the load concerning a tire accurately based on the contact area of a tire can be provided.

(A) is a figure which shows the example of 1 structure of the vehicle provided with a wheel load value calculation apparatus, (b) is a figure which shows the example of 1 structure of the sensor unit which comprises a wheel load value calculation apparatus. (A), (b) is a figure which shows the contact state of a tire and the state of a deformation | transformation of a piezoelectric element, (c) is a graph which shows the change of the voltage which a piezoelectric element generate | occur | produces. (A), (b) is a figure which shows the contact width of a tire, a deformation | transformation of a piezoelectric element, and a graph which shows the state of the voltage which a piezoelectric element generate | occur | produces. It is a figure which shows a load calculation map. It is a flowchart which shows a load calculation procedure. It is a flowchart which shows the procedure of contact area calculation. (A), (b) is the figure which shows the figure which shows the deformation | transformation of the piezoelectric element with which the width direction of the tire was equipped, and the voltage which each piezoelectric element generate | occur | produces.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings as appropriate.
The wheel load value calculation device according to the present embodiment is provided in a vehicle 1 having, for example, four wheels 20a to 20d, as shown in FIG.
The vehicle 1 preferably includes a TPMS (Tire Pressure Monitoring System) configured to include the sensor units 21 a to 21 d, the initiators 23 a to 23 d, and the control device 10.
The sensor units 21a to 21d are attached to the wheels 20a to 20d, and the air pressure measurement function for measuring the air pressure (tire air pressure) of the tires Tia to Tid attached to the tires, and the measured value of the air pressure as a signal (air pressure signal) It has a transmission function to send it on radio waves.
In addition, the control device 10 is provided with a receiving antenna 10a that receives radio waves carrying the air pressure signals transmitted from the sensor units 21a to 21d, and is configured to be able to receive radio waves transmitted from the sensor units 21a to 21d.
Since the sensor units 21a to 21d according to the present embodiment have an air pressure measurement function and a transmission function, they correspond to the air pressure measurement means and the transmission means described in the claims.

  And the air pressure signal of each wheel 20a-20d which the receiving antenna 10a received is input into the control apparatus 10, and the air pressure of tire Tia-Tid with which each wheel 20a-20d is mounted | worn by the control apparatus 10 is monitored.

As shown in FIG. 1B, the sensor unit 21a attached to the wheel 20a transmits and receives data via the air pressure sensor 210 for measuring the tire air pressure of the tire Tia and the receiving antenna 10a of the control device 10 via radio waves. A machine 211, a CPU (Central Processing Unit) 212, a memory 213 storing a program executed by the CPU 212, and a battery 214 serving as a power supply source of the sensor unit 21a.
The sensor unit 21a includes the air pressure sensor 210 to provide an air pressure measurement function, and the transmitter / receiver 211 includes a transmission function.

For example, when the sensor unit 21a configured as described above receives an activation signal transmitted from the control device 10 via the initiator 23a, the air pressure sensor 210 starts measuring the tire air pressure of the tire Tia in response to a command from the CPU 212. To do. Then, the CPU 212 sends the measurement value of the air pressure sensor 210 as an air pressure signal on the radio wave via the transceiver 211. The control device 10 takes in the air pressure signal received by the receiving antenna 10a, acquires the tire air pressure of the tire Tia, and monitors the tire air pressure.
Further, when a stop signal is transmitted from the control device 10 via the initiator 23a, the air pressure sensor 210 stops measuring the tire air pressure in response to a command from the CPU 212, and the control device 10 monitors the tire air pressure of the tire Tia. finish.

  The other sensor units 21b to 21d have the same configuration as the sensor unit 21a, and the control device 10 is configured to monitor the tire pressures of the tires Tib to Tid based on the air pressure signals transmitted from the sensor units 21b to 21d. The

In addition, the tires Tia to Tid mounted on the wheels 20a to 20d of the vehicle 1 according to the present embodiment are piezoelectric as a contact surface detection means for detecting the road surface Ro (see FIG. 2A) and the contact surface of the tire. Elements 24a to 24d are provided.
The contact surface detection means is not limited to the piezoelectric elements 24a to 24d, and the type thereof is not limited as long as it is an element (sensor) that can detect the contact surfaces of the tires Tia to Tid and the road surface Ro.
And the wheel load value calculation apparatus which concerns on this embodiment is comprised including TPMS (The sensor units 21a-21d, the initiators 23a-23d, the control apparatus 10, and the receiving antenna 10a) and the piezoelectric elements 24a-24d.

The piezoelectric elements 24a to 24d are provided to be affixed to the inner periphery of each tire Tia to Tid, for example, inside the tread, so that each piezoelectric element 24a to 24d is deformed according to the deformation of each tire Tia to Tid. Composed.
Although details will be described later, the piezoelectric elements 24a to 24d generate voltages corresponding to the deformations of the tires Tia to Tid, and the sensor units 21a to 21d receive signals inputted from the piezoelectric elements 24a to 24d as signals (tire conditions). Signal) and transmitted to the receiving antenna 10a. Further, the tire condition signal received by the receiving antenna 10 a is configured to be input to the control device 10.

As shown in FIG. 1B, in the sensor unit 21a, the voltage generated by the piezoelectric element 24a is taken into the CPU 212. Then, the CPU 212 is configured to convert the captured voltage into a tire state signal and send it on radio waves via the transceiver 211.
The other sensor units 21b to 21d have the same configuration.

Further, the piezoelectric elements 24a to 24d detect the contact surfaces of the tires Tia to Tid as follows.
As shown in FIG. 2A, a piezoelectric element 24a that generates a voltage by bending deformation is attached to the inner peripheral surface (inside the tread) of the tire Tia.
As shown in FIG. 2A, when the tire Tia contacts the road surface Ro, the tread of the tire Tia is deformed into a flat shape by a load applied to the tire Tia (tire load) to form a contact surface. .
The length in the tire circumferential direction of the contact surface at this time (the length in the direction along the outer periphery of the tire Tia) is referred to as “contact length (Lflat)”.
2A and 2B show a tire Tia mounted on the wheel 20a (see FIG. 1A). The tires Tib to Tid (see FIG. 1A) mounted on the other wheels 20b to 20d (see FIG. 1A) have the same configuration.

  As shown in FIGS. 2 (a) and 2 (b), the piezoelectric element 24a attached to the inner peripheral surface of the tire Tia is deformed along the curve of the tire Tia at a position other than the ground surface, and is applied to the ground surface. When this happens (in position), the tire Tia is bent and deformed so as to be bent. The piezoelectric element 24a is not deformed when it is on the grounding surface, and is bent and deformed again when it comes out of the grounding surface (Out position). That is, the piezoelectric element 24a is bent and deformed at the boundary where the tire Tia is deformed flat on the ground contact surface.

The voltage generated by the piezoelectric element 24a deforming in accordance with the deformation of the rotating tire Tia changes as shown in FIG. Note that FIG. 2C shows a change in voltage over time from the left to the right.
The range indicated by “A” in FIG. 2C is where the piezoelectric element 24a is not the ground contact surface (position “A” in FIG. 2B), and is curved along the curve of the tire Tia. In this way, the voltage Vlow is generated.
Further, the range indicated by “B” is the inner peripheral surface of the tire Tia that is deformed flat when the piezoelectric element 24a is at the position of the ground contact surface (the position of “B” in FIG. 2B). The deformation of the piezoelectric element 24a is eliminated. Therefore, no voltage is generated.

In addition, the piezoelectric element 24a is bent and deformed at a position approaching the ground plane (In: a boundary deformed flat on the ground plane), and generates a voltage Vpk higher than the voltage Vlow.
Similarly, the piezoelectric element 24a is bent and deformed at a position where it exits from the ground plane (Out: a boundary where the flat surface is deformed on the ground plane and returns to the curve), and generates a voltage Vpk higher than the voltage Vlow.
Hereinafter, the voltage Vpk generated by the piezoelectric element 24a at the boundary with the ground plane is referred to as a boundary voltage. In some cases, the voltage value of the boundary voltage Vpk at the position (In) where the piezoelectric element 24a approaches the ground plane is different from the voltage value of the boundary voltage Vpk at the position (Out) where the piezoelectric element 24a exits from the ground plane.

  Thus, since the piezoelectric element 24a generates the boundary voltage Vpk at the boundary where the tire Tia deforms flatly on the ground surface, for example, the control device 10 (see FIG. 1A), the piezoelectric element 24a is “In If the controller 10 is configured to be able to measure the time from the acquisition of the boundary voltage Vpk at the position "" to the acquisition of the boundary voltage Vpk at the "Out" position, the control device 10 can be used for the piezoelectric element 24a. Can be obtained as the time “Tflat” (Tflat).

Further, when the vehicle 1 (see FIG. 1A) travels on the road surface Ro without slipping the tire Tia, the tire Tia (center) of the piezoelectric element 24a at the position “In” has a contact length. The position “Out” is reached when it has moved a distance corresponding to Lflat.
The moving distance of the center of the tire Tia is the moving distance of the vehicle 1, and the product “Vcar × Tflat” of the vehicle speed Vcar and the contact time Tflat when the piezoelectric element 24a is on the contact surface is the distance that the vehicle 1 moves in the contact time Tflat. become. This distance is equal to the contact length Lflat.
From this, the control device 10 can calculate the contact length Lflat of the tire Tia when acquiring the vehicle speed Vcar of the vehicle 1 and the contact time Tflat when the piezoelectric element 24a is on the contact surface.

  As described above, the voltage generated by the piezoelectric element 24a is input to the control device 10 via the sensor unit 21a as a tire condition signal. Therefore, the control device 10 can acquire the boundary voltage Vpk generated when the piezoelectric element 24a is at the boundary with the ground plane by the tire state signal. The elapsed time from the position (In) at which the piezoelectric element 24a reaches the ground plane to the position (Out) at which the piezoelectric element 24a exits the ground plane, that is, the grounding time Tflat when the piezoelectric element 24a is on the ground plane can be calculated.

The vehicle speed Vcar of the vehicle 1 (see FIG. 1A) is preferably measured by a vehicle speed sensor (not shown), and the control device 10 (see FIG. 1A) is input from a vehicle speed sensor (not shown). The vehicle speed Vcar of the vehicle 1 may be obtained by the signal to be obtained.
With such a configuration, the control device 10 can calculate the contact length Lflat.

  The tire Tia is deformed by applying a tire load on the contact surface, and the contact surface moves in the circumferential direction (direction along the circumference of the tire Tia) with respect to the tire Tia. Change direction. The voltage generated by the piezoelectric element 24a changes due to the deformation of the tire Tia at the position where the piezoelectric element 24a is provided. From this, the piezoelectric element 24a has a circumferential load change (along the circumference of the tire Tia) accompanying a change in the tire load applied to the tire Tia when the vehicle 1 (see FIG. 1A) travels. It has a function of detecting a change in tire load). Therefore, the piezoelectric element 24a according to the present embodiment is a first detection unit described in the claims.

  Further, as shown in FIG. 3A, it is preferable that a plurality of piezoelectric elements 24a be provided in one row in the width direction of the tire Tia. For example, FIG. 3A shows a state in which seven piezoelectric elements 24a1 to 24a7 are provided in the width direction of the tire Tia.

As described above, when the vehicle 1 (see FIG. 1A) travels when the tire Tia rotates, the piezoelectric element 24a disposed at the position serving as the ground plane is the point In shown in FIG. After the boundary voltage Vpk is generated, the voltage is no longer generated, and the boundary voltage Vpk is generated again at the point Out.
However, as shown in FIG. 3A, both lateral portions of the ground contact surface are not deformed in the width direction of the tire Tia. Therefore, even when the tire Tia rotates and the vehicle 1 travels, the piezoelectric elements 24a disposed on both sides of the ground contact surface in the tire Tia always generate the voltage Vlow shown in FIG.

As shown in FIG. 3A, when seven piezoelectric elements 24a1 to 24a7 are provided in the width direction of the tire Tia, the three piezoelectric elements 24a3 to 24a5 (black) provided in the substantially central portion in the width direction of the tire Tia are , The generated voltage changes as indicated by the solid line in the lower graph.
On the other hand, the piezoelectric elements 24a1, 24a2, 24a6, and 24a7 (white) arranged on both sides of the position to be the ground plane do not undergo deformation due to the deformation of the tire Tia, and the lower part of FIG. The voltage Vlow is always generated as indicated by the broken line in FIG.

For example, when the load applied to the tire Tia increases or when the tire air pressure of the tire Tia is reduced, the ground contact surface extends in the width direction of the tire Tia, and as shown in FIG. 3B, the piezoelectric elements 24a2 to 24a6. (Black) is in a state of being arranged at a position to be a ground plane. That is, in the piezoelectric elements 24a2 to 24a6 shown in black, the generated voltage changes as shown by the solid line in the lower graph.
On the other hand, the piezoelectric elements 24a1, 24a7 (white) arranged on both sides of the position to be the ground contact surface are not deformed due to the deformation of the tire Tia, and the broken line in the lower graph of FIG. As shown, a voltage of Vlow is always generated.

  Therefore, the control device 10 (see (a) of FIG. 1) acquires the generated voltages of the piezoelectric elements 24a1 to 24a7 as tire state signals, and is shown by the solid lines in the graphs of (a) and (b) of FIG. The length in the width direction of the tire Tia on the ground contact surface is calculated based on the piezoelectric element 24a whose voltage changes at the same time. The length in the width direction of the tire Tia on the ground contact surface is referred to as “ground contact width (Wflat)”.

For example, when the generated voltage of the piezoelectric elements 24a3 to 24a5 (black) changes so as to generate the boundary voltage Vpk as shown by a solid line in the graph below (a) of FIG. In (a), a range where the piezoelectric elements 24a3 to 24a5 are provided is defined as a ground width Wflat.
In addition, as shown by the solid line in the lower graph of FIG. 3B, when the generated voltage of the piezoelectric elements 24a2 to 24a6 (black) changes so as to generate the boundary voltage Vpk, the control device 10 (in FIG. 1) In (a), the range in which the piezoelectric elements 24a2 to 24a6 are provided is defined as a ground width Wflat.
As described above, a plurality of piezoelectric elements 24a (24a1 to 24a7) according to the present embodiment are provided in the width direction of the tire Tia, so that the vehicle 1 (see FIG. 1A) travels in the width direction of the tire Tia. Detect deformation of As described above, since the tire Tia is deformed by applying a tire load on the contact surface, the plurality of piezoelectric elements 24a1 to 24a7 provided in the width direction of the tire Tia are in the width direction according to a change in the tire load applied to the tire Tia. Has a function of detecting a change in load (change in tire load along the width direction of the tire Tia). Therefore, the piezoelectric elements 24a (24a1 to 24a7) according to the present embodiment serve as second detection means described in the claims.

  A map showing the relationship between the number of piezoelectric elements 24a whose generated voltage changes so as to generate the boundary voltage Vpk and the length of the ground contact width of the tire Tia is created in advance, and the control device 10 ((a) in FIG. 1). The control device 10 can easily calculate the grounding width by referring to the map based on the change in the voltage generated by the piezoelectric element 24a.

As described above, the control device 10 can calculate the contact length Lflat and the contact width Wflat in the tire Tia. Then, the contact area Sflat of the tire Tia can be calculated by multiplying the contact length and the contact width. That is, “Sflat = Lflat × Wflat” can be set.
Of course, the number of piezoelectric elements 24a provided in the width direction of the tire Tia is not limited to seven. With the configuration in which seven or more piezoelectric elements 24a are provided in one row in the width direction of the tire Tia, the control device 10 (see FIG. 1A) can calculate the ground contact width Wflat with higher accuracy, and consequently the ground contact of the tire Tia. The area Sflat can be calculated with higher accuracy.

Further, the tires Tib to Tid (see FIG. 1A) attached to the wheels 20b to 20d (see FIG. 1A) also have piezoelectric elements 24b to 24d (see FIG. )), The control device 10 can calculate the contact area Sflat of the tires Tib to Tid.
In this case, the piezoelectric elements 24b to 24d also function as first detection means and second detection means.

And control device 10 (refer to (a) of Drawing 1) concerning this embodiment is based on contact area Sflat computed for every tire Tia-Tid (refer to (a) of Drawing 1), each tire Tia- A load value (tire load value) applied to Tid is calculated.
For example, the control device 10 calculates the tire load value based on the tire contact area Sflat and the tire air pressure.
As shown in the map (load calculation map) shown in FIG. 4, there is a linear correlation between the tire contact area Sflat and the tire load for each tire pressure (P1, P2 and P3 are illustrated in FIG. 4). It is known that this correlation can be easily obtained by experimental measurement or the like.

Therefore, a load calculation map (refer to FIG. 4) showing a correlation between the tire contact area Sflat, the tire load, and the tire pressure, which is obtained in advance by experimental measurement or the like, is the control device 10 (refer to (a) in FIG. 1). What is necessary is just to set it as the structure memorize | stored in the memory | storage part which is not shown in figure.
Such a load calculation map is easily obtained by, for example, measuring the change in the contact area Sflat accompanying the change in the tire load for each tire pressure and performing regression analysis (eg, the least square method) on the collected data.

Then, after calculating the contact area Sflat of each tire Tia to Tid, the control device 10 calculates the tire pressure of each tire Tia to Tid measured by the air pressure sensors 22a to 22d (see FIG. 1A) and the calculated ground contact. Based on the area Sflat, the load calculation map is referred to, and the tire load values of the tires Tia to Tid are calculated.
That is, the control device 10 uses a load calculation map (correlation between the tire contact area Sflat, the tire load, and the tire pressure) based on the calculated value of the contact area Sflat of each tire Tia to Tid and the measured value of the tire pressure. The tire load values of the tires Tia to Tid are calculated.

  Specifically, the control device 10 selects, from the load calculation map (see FIG. 4), characteristic lines corresponding to the tire pressures of the tires Tia to Tid measured by the air pressure sensors 22a to 22d (see (a) of FIG. 1). . And the control apparatus 10 makes the tire load value corresponding to the calculated contact area Sflat the tire load value of each tire Tia-Tid on the selected characteristic line. At this time, if the tire air pressure of each tire Tia to Tid is an intermediate value of the tire air pressure shown in the load calculation map (for example, between P1 and P2 in FIG. 4), the control device 10 performs proportional distribution or the like on each tire. The tire load values of Tia to Tid are calculated.

Since the load calculation map (see FIG. 4) showing the correlation between the tire contact area Sflat and the tire load is obtained by experimental measurement or the like, it is possible to obtain data with small error by reducing the measurement error during the experimental measurement. .
Further, the contact area Sflat of each tire Tia to Tid (see FIG. 1A) is a value calculated based on the deformation caused by the tire load applied to each tire Tia to Tid, and the error is small.
Accordingly, the tire load values of the tires Tia to Tid calculated based on the tire contact area Sflat calculated with a small error and the load calculation map with a small error have a small error. That is, the wheel load value calculation device according to the present embodiment can calculate the tire load values of the tires Tia to Tid with high accuracy.
The load calculation map may be configured to correspond to each of the tires Tia to Tid, for example. When all the tires Tia to Tid are the same, one load calculation map is used. The structure provided may be sufficient.

  Further, for example, a load calculation map corresponding to the tire Tia is stored in the memory 213 (see FIG. 1B) of the sensor unit 21a (see FIG. 1B). The structure transmitted to (a) of FIG. 1 may be sufficient. For example, when the wheel 20a (see FIG. 1A) is attached to the vehicle body 1a (see FIG. 1A) and the sensor unit 21a is first activated, the sensor unit 21a controls the load calculation map. What is necessary is just to set it as the structure transmitted to the apparatus 10. FIG. Then, if the control device 10 is configured to store the transmitted load calculation map in a storage unit (not shown), when the tire Tia is changed due to the replacement of the wheel 20a, the control device 10 corresponds to the changed tire Tia. Load calculation map to be acquired. Moreover, what is necessary is just to set it as an equivalent structure also about the other wheels 20b-20d (refer (a) of FIG. 1).

Moreover, it is good also as a structure by which the arithmetic expression which calculates a tire load value from the tire contact area Sflat and a tire air pressure is integrated in the program performed when the control apparatus 10 calculates a tire load value. In this case, the control device 10 (see FIG. 1A) need not include the load calculation map shown in FIG.
Similar to the load calculation map, such a calculation formula can be easily obtained by measuring the change in the contact area Sflat accompanying the change in the tire load for each tire pressure and performing regression analysis (eg, least square method) on the collected data. Desired.

Further, as shown in the load calculation map, since there is a correlation expressed by a linear expression (straight line) between the tire contact area Sflat and the tire load, the tire load value is calculated from the tire contact area Sflat and the tire pressure. The arithmetic expression to be performed is also expressed by a primary expression. Therefore, even if it is the structure which calculates a tire load value using a computing equation, the calculation load of the control apparatus 10 is small.
Even in this configuration, the control device 10 uses the correlation between the tire contact area Sflat, the tire load, and the tire pressure based on the calculated value of the contact area Sflat of each tire Tia to Tid and the measured value of the tire pressure. Thus, the tire load values of the tires Tia to Tid are calculated.

As described above, the wheel load value calculation device according to the present embodiment can accurately calculate the tire load values of the tires Tia to Tid from the tire contact area Sflat and the tire air pressure.
Then, the control device 10 (see FIG. 1A) according to the present embodiment uses the calculated tire load value to overload the tire and overload the vehicle 1 (see FIG. 1A). The loading state can be accurately determined.
As described above, the tire load value obtained by the prior art has a large error, and there is a high risk of misjudgment when used for the determination of the tire overload state and the determination of the overload state. It was difficult to use the tire load value to determine the overloading state.
Since the wheel load value calculation apparatus according to the present embodiment can calculate the tire load value with high accuracy, it is possible to improve the accuracy of the determination of the tire overload state and the determination of the overload state.

《Overload judgment unit》
When the load (tire load value) applied to the tires Tia to Tid (see FIG. 1A) exceeds the maximum load capacity (maximum load) of each tire Tia to Tid (overload state), The control device 10 can be configured to determine an overload state of the tire and issue an alarm, for example.
The maximum load capacity of each tire Tia to Tid is a value set in advance as a characteristic value, and the control device 10 (see FIG. 1A) stores the maximum load capacity in a storage unit (not shown). Is preferred.

The control device 10 (see FIG. 1A) calculates the ground contact area Sflat of the tire Tia (see FIG. 1A) based on the voltage generated by the piezoelectric elements 24a1 to 24a7 as described above, and the air pressure The tire pressure measured by the sensor 210 (see FIG. 1A) is acquired. Further, the tire load value of the tire Tia is calculated with reference to the load calculation map (see FIG. 4) based on the calculated contact area Sflat and the tire air pressure.
When the calculated tire load value exceeds the maximum load capacity (maximum load) of the tire Tia, the control device 10 determines that the tire Tia is in an overload state, and for example, an alarm device (warning lamp) (not shown) The warning sound) is activated to notify the driver or the like of the overload state.

Alternatively, when the ratio of the tire load to the maximum load capacity (tire load ratio = tire load / maximum load capacity) exceeds a predetermined threshold (for example, 80%), the control device 10 indicates that the tire Tia is in an overload state. It may be configured to determine that there is.
This threshold value may be a value that is appropriately determined by, for example, experimental measurement.

  The control device 10 similarly calculates tire load values for tires Tib to Tid (see FIG. 1A) other than the tires Tia (see FIG. 1A), and determines the tires Tib to Tid. A configuration for determining that each tire Tib to Tid is in an overload state when a tire load value exceeding the maximum load capacity is calculated or when a tire load factor of each tire Tib to Tid exceeds a predetermined threshold value Is preferred.

  With this configuration, an overload determination unit (not shown) that determines the overload state of the tires Tia to Tid is a wheel load value calculation device provided in the control device 10 (see FIG. 1A). be able to.

《Overload determination unit》
The total load applied to the tires Tia to Tid (see FIG. 1A) is the total vehicle weight of the vehicle 1 (see FIG. 1A) (the vehicle weight, the weight of all passengers, and the weight of the load). Total). Therefore, the control device 10 (see FIG. 1A) can calculate the load weight (the sum of the weight of the passenger and the weight of the load) from the tire load values of the tires Tia to Tid and the vehicle weight. In other words, the tire load values of the calculated tires Tia to Tid are summed to calculate the vehicle total weight of the vehicle 1, and further the subtracted vehicle weight is subtracted from the calculated vehicle total weight to calculate the loaded weight. it can.

When the load weight exceeds the maximum load weight set for each vehicle 1 (see FIG. 1A), the control device 10 (see FIG. 1A) causes the vehicle 1 to be overloaded. For example, it is determined that the vehicle is in an overloaded state by operating an alarm device (warning light, warning sound) (not shown) to determine that the vehicle is overloaded.
With this configuration, an overload determination unit (not shown) that determines the overload state of the vehicle 1 can be used as a wheel load value calculation device provided in the control device 10.
The vehicle weight and the maximum load weight are preferably stored as a characteristic value of the vehicle 1 in a storage unit (not shown) of the control device 10.

With reference to FIG. 5, a description will be given of a procedure (load calculation procedure) in which the control device 10 including an overload determination unit and an overload determination unit calculates tire load values and determines an overload state and an overload state. 1 to 4 as appropriate).
In addition, this load calculation procedure is a procedure for the control device 10 to execute a program for controlling the wheel load value calculation device. For example, this program is incorporated in the program for the control device 10 to control TPMS as a subroutine. do it.
For example, the control device 10 may be configured to periodically execute a load calculation procedure at a predetermined interval.

When starting the load calculation procedure, the control device 10 acquires tire pressures of the tires Tia to Tid from the sensor units 21a to 21d (step S1).
For example, if the control device 10 transmits an air pressure request signal to the sensor units 21a to 21d via the initiators 23a to 23d, and the sensor units 21a to 21d transmit air pressure signals according to the air pressure request signal, the control device 10 can acquire the tire pressure of each tire Tia-Tid when the load calculation procedure is started.

  And the control apparatus 10 calculates the contact area Sflat of all the tires Tia-Tid (step S2).

  With reference to FIG. 6, the procedure in which the control apparatus 10 calculates the contact area Sflat of all the tires Tia to Tid will be described. Although the calculation of the contact area Sflat of the tire Tia will be described with reference to FIG. 6, the control device 10 similarly calculates the contact areas Sflat of the other tires Tib to Tid. When the contact area Sflat of all tires Tia to Tid is calculated, the control device 10 ends the procedure for calculating the contact area Sflat.

  The control device 10 waits until the boundary voltage Vpk is acquired from the sensor unit 21a when the piezoelectric element 24a (24a1 to 24a7) approaches the ground plane (the position “In” in FIG. 2C) ( If the boundary voltage Vpk is acquired (step S200 → No) (step S200 → Yes), the control device 10 calculates the ground contact width Wflat of the tire Tia (step S201).

For example, the control device 10 transmits a ground information request signal for requesting a tire condition signal to the sensor unit 21a, and in the sensor unit 21a that has received the ground information request signal, at least one of the piezoelectric elements 24a1 to 24a7 generates the boundary voltage Vpk. Then, all the voltages generated by the piezoelectric elements 24a1 to 24a7 may be transmitted as tire condition signals.
When the sensor unit 21a generates the boundary voltage Vpk after the piezoelectric elements 24a1 to 24a7 generate the voltage Vlow shown in FIG. 2C, the sensor unit 21a transmits the boundary voltage Vpk, thereby transmitting the piezoelectric element 24a1. The boundary voltage Vpk when ˜24a7 approaches the ground plane can be transmitted.

Furthermore, the voltages generated by the piezoelectric elements 24a1 to 24a7 are individually input to the CPU 212 of the sensor unit 21a, and the CPU 212 individually converts the voltages generated by the piezoelectric elements 24a1 to 24a7 into tire state signals and transmits and receives them. The control device 10 can individually acquire the voltages generated by the piezoelectric elements 24a1 to 24a7 and specify the piezoelectric element 24a that has generated the boundary voltage Vpk.
Then, the control device 10 identifies the piezoelectric element 24a that has generated the boundary voltage Vpk among the piezoelectric elements 24a1 to 24a7, and sets the range including the piezoelectric element 24a that has generated the boundary voltage Vpk as the ground width Wflat of the tire Tia.

After calculating the ground contact width Wflat in this way (step S201), the control device 10 is when the piezoelectric element 24a (24a1 to 24a7) comes out of the ground surface (position "Out" in FIG. 2C). Until the boundary voltage Vpk is acquired (step S203 → No), the time is measured (step S202).
The sensor unit 21a transmits the boundary voltage Vpk when the piezoelectric element 24a approaches the ground plane, and then when at least one of the piezoelectric elements 24a1 to 24a7 generates the boundary voltage Vpk, the piezoelectric element 24a is moved from the ground plane. Transmit as boundary voltage Vpk when exiting.

When the control device 10 acquires the boundary voltage Vpk when the piezoelectric element 24a (24a1 to 24a7) exits from the ground plane (step S203 → Yes), the control device 10 determines the time until the piezoelectric element 24a acquires the boundary voltage Vpk. The ground contact time Tflat on the ground plane is assumed.
Further, the control device 10 acquires the vehicle speed Vcar of the vehicle 1 (step S204), and calculates the contact length Lflat of the tire Tia from the contact time Tflat and the acquired vehicle speed Vcar (step S205). Specifically, the control device 10 sets “Vcar × Tflat” as the ground contact length Lflat.

Then, the control device 10 multiplies the calculated contact width Wflat and the contact length Lflat to calculate the contact area Sflat of the tire Tia (step S206).
The control device 10 similarly calculates the contact area Sflat for the tires Tib to Tid other than the tire Tia.
Then, when the contact area Sflat is calculated for all the tires Tia to Tid, step S2 in FIG. 5 is completed, and the procedure proceeds to step S3 in FIG.

In step S3, the control device 10 calculates tire load values of all tires Tia to Tid.
The control device 10 calculates the tire load value of the tire Tia with reference to the load calculation map shown in FIG. 4 based on the tire air pressure of the tire Tia and the contact area Sflat of the tire Tia. Further, tire load values are similarly calculated for the other tires Tib to Tid (step S3).
Then, the control device 10 calculates the tire load factor for each of the tires Tia to Tid, and determines whether or not the tire load factor exceeds a predetermined threshold value for all the tires Tia to Tid (step S4).

When at least one tire load factor among the tires Tia to Tid exceeds the threshold value (step S4 → Yes), the control device 10 determines that the state is an overload state (step S5).
In this case, the control device 10 may be configured to operate an alarm device (warning light, warning sound) (not shown).

In step S4, when the tire load factors of all tires Tia to Tid are equal to or less than a predetermined threshold (step S4 → No), the control device 10 calculates the total vehicle weight of the vehicle 1 (step S6), and further determines the loaded weight. Calculate (step S7).
Specifically, the control device 10 calculates the total vehicle weight by adding the tire load values of all the tires Tia to Tid.
In addition, the control device 10 subtracts a predetermined vehicle weight from the total vehicle weight to calculate the loaded weight.

Then, the control device 10 compares the calculated load weight with a predetermined maximum load weight (step S8). If the load weight is larger than the maximum load weight (step S8 → Yes), the vehicle 1 is overloaded. The state is determined (step S9).
In this case, the control device 10 may be configured to operate an alarm device (warning light, warning sound) (not shown).
On the other hand, when the loaded weight is equal to or smaller than the maximum loaded weight (step S8 → No), the control device 10 ends the load calculation procedure without determining that the overloaded state is present.

The load calculation procedure shown in FIG. 5 is a configuration in which the control device 10 determines that the vehicle is overloaded when the tire load factor of one of the tires Tia to Tid is larger than a predetermined threshold (step S4 → Yes). However, when the tire load value of one of the tires Tia to Tid is larger than the maximum load capacity (maximum load) of the tires Tia to Tid, the control device 10 determines that the vehicle is overloaded. Also good.
In this case, in step S4, the control device 10 compares the tire load value of each tire Tia-Tid with the maximum load capacity of each tire Tia-Tid, and at least one of the tires Tia-Tid has the maximum tire load value. When the load capacity is exceeded, the control device 10 determines to be in an overload state.

As described above, in the wheel load value calculation device according to the present embodiment, the control device 10 (see FIG. 1A) executes the load calculation procedure, whereby all tires Tia to Tid (( The tire load value of a) can be calculated for each tire.
The tire load value calculated in this way is a value calculated based on the contact area Sflat of the tires Tia to Tid, and is calculated with high accuracy with little error.
Furthermore, the control device 10 can determine the overload state of each tire Tia to Tid and the overload state of the vehicle 1 (see FIG. 1A) with high accuracy by using a tire load value with less error. it can.
And the tire durability fall, the fall of operation stability, the fall of braking force, etc. resulting from the tires Tia-Tid in an overload state and the vehicle 1 in an overload state are prevented.

  Each tire Tia to Tid (see FIG. 1A) is not a sensor capable of directly measuring a tire load value, but a detection means (first detection means, second detection) capable of detecting a change in tire load. In other words, inexpensive elements such as the piezoelectric elements 24a to 24d (see FIG. 1A) can be used as in the wheel load value calculation device according to the present embodiment. Therefore, the tire load value can be accurately calculated without increasing the production cost of the vehicle 1 (see FIG. 1A).

  Further, the voltage generated by the piezoelectric elements 24a to 24d (see FIG. 1A) provided in the tires Tia to Tid is converted into the tire state by the sensor units 21a to 21d (see FIG. 1A) constituting the TPMS. It can convert into a signal and can transmit to the control apparatus 10 (refer Fig.1 (a)) of the vehicle main body 1a. Therefore, there is no need to newly provide a device for transmitting the voltage generated by the piezoelectric elements 24a to 24d to the control device 10, and the production cost of the wheels 20a to 20d (see FIG. 1A) can be kept low. The production cost of the vehicle 1 can be kept low.

The configuration in which the control device 10 (see FIG. 1A) calculates the contact area Sflat of the tires Tia to Tid (see FIG. 1A) may be, for example, as follows.
The following description will be made with the tire Tia of the wheel 20a (see FIG. 1A), but the tires Tib to Tid of the other wheels 20b to 20d (see FIG. 1A) (see FIG. 1A). ) May have the same configuration.

  As shown in FIG. 7A, the tire Tia bends at the boundary between the ground contact surface and both lateral portions thereof. Therefore, for example, as shown in FIGS. 7A and 7B, a plurality of piezoelectric elements 24a (6A in FIG. 7A and FIG. 7B) are arranged in the width direction of the tire Tia as a contact surface detection means. And the control device 10 (see FIG. 1A) bends and deforms between the ground plane and both lateral portions of the plurality of piezoelectric elements 24a1 to 24a6. The ground width Wflat is calculated based on the piezoelectric elements 24a1 to 24a6 that generate the boundary voltage Vpk shown in the lower graph.

For example, in FIG. 7A, the black piezoelectric elements 24a2 and 24a5 are bent and deformed, and the white piezoelectric elements 24a3 and 24a4 are located at the position of the ground plane and the deformation is eliminated. Further, the white piezoelectric elements 24a1 and 24a6 are curved along the shape of both lateral portions of the ground plane. Accordingly, the voltages generated by the piezoelectric elements 24a1 to 24a6 at this time are indicated by black circles in the lower graph. The piezoelectric elements 24a1 and 24a6 (white) are deformed so as to be curved, and generate a voltage Vlow lower than the boundary voltage Vpk. The piezoelectric elements 24a3 and 24a4 (white) are not deformed and do not generate voltage.
In this state, the control device 10 (see FIG. 1A) sets the range including the piezoelectric elements 24a2 to 24a5 (black) as the ground width Wflat.

On the other hand, in FIG. 7B, the black piezoelectric elements 24a1 and 24a6 are bent and deformed, and the white piezoelectric elements 24a2 to 24a5 are located on the ground plane and the deformation is eliminated. Accordingly, the voltages generated by the piezoelectric elements 24a1 to 24a6 at this time are indicated by black circles in the lower graph.
In this state, the control device 10 (see FIG. 1A) sets a range in which the piezoelectric elements 24a1 to 24a6 (black) are provided as the ground width Wflat.

  Further, when all the piezoelectric elements 24a1 to 24a6 are not located on the ground plane, there is no piezoelectric element 24a1 to 24a6 that bends and deforms between the ground plane and both lateral portions, and the piezoelectric elements 24a1 to 24a6 that generate the boundary voltage Vpk. Absent. Therefore, the control device 10 (see FIG. 1A) acquires the grounding time Tflat when the piezoelectric element 24a is on the ground plane by measuring the time during which the piezoelectric elements 24a1 to 24a6 that generate the boundary voltage Vpk exist. it can. Alternatively, the controller 10 may acquire the grounding time Tflat when the piezoelectric element 24a is on the ground plane by measuring the time during which the piezoelectric elements 24a1 to 24a6 that do not generate voltage exist. Then, as described above, by acquiring the vehicle speed Vcar of the vehicle 1 (see FIG. 1A), the control device 10 can calculate the contact area Sflat of the tire Tia.

  Even with such a configuration, the control device 10 (see FIG. 1A) can calculate the contact area Sflat of each tire Tia to Tid (see FIG. 1A).

  In addition, the configuration of the contact surface detection means is not limited as long as the contact length Lflat and the contact width Wflat of the tires Tia to Tid (see FIG. 1A) can be detected.

DESCRIPTION OF SYMBOLS 1 Vehicle 1a Vehicle main body 10 Control apparatus (wheel load value calculation apparatus)
20a-20d wheel 21a-21d sensor unit (pneumatic measurement means, transmission means, wheel load value calculation device)
24a to 24d Piezoelectric elements (first detection means, second detection means, wheel load value calculation device)
Tia to Tid tires

Claims (6)

An air pressure measuring means for measuring an air pressure of a tire mounted on a wheel of the vehicle;
First detecting means for detecting a change in a circumferential direction of a load applied to the tire when the vehicle travels;
Second detection means for detecting a change in the width direction of the load;
A wheel load value calculating device comprising a control device for calculating the value of the load,
The controller is
Calculating a contact area of the tire based on a contact length in the circumferential direction of the tire calculated from a change in the circumferential direction of the load and a contact width in the width direction of the tire calculated from a change in the width direction of the load; Based on the calculated value of the ground contact area and the measured value of the tire air pressure measured by the air pressure measuring means, the load is calculated using the correlation between the ground contact area and the load value set for each air pressure. The wheel load value calculation device characterized by calculating the value of. The first detection means and the second detection means are:
A piezoelectric element that is attached to the inner peripheral surface of the tire and is deformed along with the deformation of the tire at a boundary where the tire deforms flatly on the ground contact surface, and generates a voltage that becomes a boundary voltage as a detection value. The wheel load value calculation device according to claim 1, wherein The detection values of the first detection means and the second detection means are:
The wheel load value calculation device according to claim 2, wherein the wheel load value calculation device is transmitted to the control device by a transmission device that transmits a measurement value of the air pressure measurement device attached to the wheel to the control device provided in a vehicle body. The controller is
When the load value calculated using the correlation based on the calculated value of the ground contact area and the measured value of the air pressure exceeds the maximum load capacity of the tire, an overload condition is determined. The wheel load value calculation device according to any one of claims 1 to 3, further comprising a load determination unit. The controller is
The tire load factor calculated based on the load value calculated using the correlation based on the calculated value of the ground contact area and the measured value of the air pressure and the maximum load capacity of the tire is a predetermined value. The wheel load value calculation device according to any one of claims 1 to 3, further comprising an overload determination unit that determines an overload state of the tire when a threshold value is exceeded. The controller is
The vehicle total weight of the vehicle is calculated from the load value calculated using the correlation based on the calculated value of the ground contact area and the measured value of the air pressure, and is preset from the calculated total vehicle weight. 6. An overload determination unit that determines an overload state of the vehicle when a value obtained by subtracting the vehicle weight exceeds a maximum load weight set for the vehicle. The wheel load value calculation device according to any one of the above.

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