JP5149531B2 - Method for detecting decrease in tire air pressure - Google Patents

Description

  The present invention relates to a tire pressure drop detecting method for detecting a tire pressure drop by a strain output of a strain sensor for measuring tire surface strain.

  The Tire Pressure Monitoring System (TPMS), which monitors the air pressure (internal pressure) filled in pneumatic tires, has traditionally been equipped with air pressure sensors on the tire wheel rim and air valve to directly measure tire pressure. So-called direct TPMS is often used.

  However, in this direct type TPMS, since a pneumatic sensor having a certain weight is attached to the wheel rim or the like at one place, there is a tendency to impair the weight balance of the wheel. Therefore, there is a problem that the weight of the wheel is increased, for example, it is necessary to attach a counterweight at a symmetrical position and cancel the weight imbalance.

  On the other hand, as described in Patent Document 1, the present applicant provides three or more strain sensors in the sidewall portion, and uses the strain sensor to measure surface strains at predetermined three measurement positions in the sidewall portion. A technique is proposed in which the three translational forces of the longitudinal force Fx, the lateral force Fy, and the vertical load Fz acting on the tire are respectively estimated by the simultaneous measurement and the three strain outputs.

Japanese Patent Laid-Open No. 2005-126008

This technique is described as follows. First, in the sidewall portion, when a longitudinal force Fx, a lateral force Fy, and a vertical load Fz, which are three translational direction forces, are individually applied to the tire, the surface strain ε generated at that time causes each directional force Fx, Fy, Fz. And have a substantially linear correlation with each other. Therefore, in the sidewall portion, the surface strain εx generated by the longitudinal force Fx can be approximated by a linear function εx = f (Fx) of the longitudinal force Fx. Similarly, the surface strain εy generated by the lateral force Fy is The surface strain εz generated by the linear function εy = f (Fy) of the force Fy and the vertical load Fz can be approximated by the linear function εz = f (Fz) of the vertical load Fz. Accordingly, the surface strain ε generated when the resultant force F of the three translational direction forces Fx, Fy, and Fz acts can be approximated by the sum of the surface strains εx, εy, and εz, that is, the following equation (a). Become.
ε = εx + εy + εz = f (Fx) + f (Fy) + f (Fz) --- (a)

  Further, in order to derive the three translational forces Fx, Fy, and Fz that form the resultant force F from the surface strain ε that can be measured by the strain sensor, the ternary linear equation (a) that uses Fx, Fy, and Fz as unknowns. This can be achieved by solving the equation. For that purpose, it is necessary to simultaneously measure the surface strain ε at three different positions to form three simultaneous equations.

In other words, three or more strain sensors are provided in the sidewall portion, and the surface strain ε is simultaneously measured at three different measurement positions. Fx, Fy, and Fz can be obtained by establishing the following three simultaneous equations from the three measured values (distortion outputs) t1, t2, and t3 at that time and solving them.
t1 = A1 · Fx + B1 · Fy + C1 · Fz
t2 = A2 · Fx + B2 · Fy + C2 · Fz
t3 = A3 · Fx + B3 · Fy + C3 · Fz

Therefore, the present inventor conducted research while paying attention to the above technique of Patent Document 1. As a result, the tire deformation is strictly a six-component force (the longitudinal force Fx, the lateral force Fy, the vertical load Fz, the overturning moment Mx, the rolling resistance moment My, the self-aligning torque Mz) that is the basic force acting on the tire. In addition, the tire surface strain ε generated during running is influenced by the surface strain εx generated by the longitudinal force Fx and the surface strain εy generated by the lateral force Fy. A surface strain εz generated by the vertical load Fz, a surface strain εmx generated by the overturning moment Mx, a surface strain εmy generated by the rolling resistance moment My, a surface strain εmz generated by the self-aligning torque Mz, It can be expressed by the following equation (b) which is the sum of the surface strain εp generated by the air pressure P And each surface strain εx, εy, εz, εmx, εmy, εmz, εp was investigated that can be approximated by a linear function of each element.
ε = εx + εy + εz + εmx + εmy + εmz + εp −−− (b)

Accordingly, in order to derive each of the seven elements Fx, Fy, Fz, Mx, My, Mz, and P from the surface strain ε, seven measured values (strain output) are obtained by simultaneously measuring the surface strain ε at seven different positions. ) By obtaining t1 to t7 and solving the following seven simultaneous equations, it is possible to obtain the unknown elements Fx, Fy, Fz, Mx, My, Mz, and P.
t1 = a1 · Fx + b1 · Fy + c1 · Fz + d1 · Mx + e1 · My + g1 · Mz + h1 · P
t2 = a2, Fx + b2, Fy + c2, Fz + d2, Mx + e2, My + g2, Mz + h2, P
t3 = a3 · Fx + b3 · Fy + c3 · Fz + d3 · Mx + e3 · My + g3 · Mz + h3 · P
t4 = a4 · Fx + b4 · Fy + c4 · Fz + d4 · Mx + e4 · My + g4 · Mz + h4 · P
t5 = a5 · Fx + b5 · Fy + c5 · Fz + d5 · Mx + e5 · My + g5 · Mz + h5 · P
t6 = a6 · Fx + b6 · Fy + c6 · Fz + d6 · Mx + e6 · My + g6 · Mz + h6 · P
t7 = a7 · Fx + b7 · Fy + c7 · Fz + d7 · Mx + e7 · My + g7 · Mz + h7 · P

  That is, by using at least seven sensor element units and simultaneously measuring tire surface strain at seven positions by using the seven sensor element units, the air pressure P, which is indispensable in the tire pressure monitoring system (TPMS), is obtained. It is possible to detect together with three translational direction forces (Fx, Fy, Fz) that are useful in the control system.

  In this method, a pneumatic sensor such as the direct TPMS is not used, and a sensor element unit for detecting three translational direction forces can be used. Therefore, the cost can be reduced. In addition, since at least seven sensor element units are mounted in a distributed manner in the circumferential direction, it is possible to maintain the weight balance of the wheel and suppress the increase in the weight of the wheel, such as eliminating the need for a counterweight for the air pressure sensor. it can.

  As described above, the present invention is based on the simultaneous measurement of tire surface strains at seven positions depending on the strain sensor, while reducing the cost and suppressing the decrease in the weight balance of the wheels and the increase in the weight while suppressing the tire air pressure. An object of the present invention is to provide a method for detecting a decrease in tire air pressure that can be easily and accurately detected.

In order to achieve the above object, the invention of claim 1 of the present application is a tire pressure drop detection method for detecting a tire pressure drop by a strain output of a strain sensor attached to a tire and measuring a tire surface strain.
It said strain sensor comprises eight sensor element unit that is spaced circumferentially in the region of the sidewall portion, and eight from the simultaneously measured eight strain output by the sensor element unit of seven distortion output By selecting, creating eight different distortion output combinations consisting of seven distortion outputs,
When the seven distortion outputs in each distortion output combination are defined as t1 to t7, the seven distortion outputs t1 to t7 are applied to the following estimation equation (1) for each distortion output combination , An estimation step for obtaining a tire pressure P for each output combination ;
And a determination step for determining a decrease in tire air pressure by comparing an average air pressure obtained by averaging a total of eight estimated air pressures P obtained in the estimation step with a preset reference air pressure,
The sensor element unit has a built-in transmission means for transmitting the measured distortion output to the electronic control device on the vehicle side, and the transmission means includes a semiconductor in which a transmission / reception circuit, a control circuit, and a memory are chipped, an antenna, When the interrogation radio wave is received from the vehicle-side electronic control unit, it can be used as electrical energy and the distortion output data in the memory can be transmitted as a response radio wave.
┌Fx┐ ┌a1 b1 c1 d1 e1 g1 h1┐-1 ┌t1┐
│Fy│ │a2 b2 c2 d2 e2 g2 h2│ │t2│
│Fz│ │a3 b3 c3 d3 e3 g3 h3│ │t3│
│Mx│ = │a4 b4 c4 d4 e4 g4 h4│ │t4│
│My│ │a5 b5 c5 d5 e5 g5 h5│ │t5│
│Mz│ │a6 b6 c6 d6 e6 g6 h6│ │t6│
└P ┘ 7a7 b7 c7 d7 e7 g7 h7┘ └t7┘
---- (1)
The symbols a1 to a7, b1 to b7, c1 to c7, d1 to d7, e1 to e7, g1 to g7, and h1 to h7 in the estimation formula (1) are coefficients,
t1 = a1 · Fx + b1 · Fy + c1 · Fz + d1 · Mx + e1 · My + g1 · Mz + h1 · P
t2 = a2, Fx + b2, Fy + c2, Fz + d2, Mx + e2, My + g2, Mz + h2, P
t3 = a3 · Fx + b3 · Fy + c3 · Fz + d3 · Mx + e3 · My + g3 · Mz + h3 · P
t4 = a4 · Fx + b4 · Fy + c4 · Fz + d4 · Mx + e4 · My + g4 · Mz + h4 · P
t5 = a5 · Fx + b5 · Fy + c5 · Fz + d5 · Mx + e5 · My + g5 · Mz + h5 · P
t6 = a6 · Fx + b6 · Fy + c6 · Fz + d6 · Mx + e6 · My + g6 · Mz + h6 · P
t7 = a7 · Fx + b7 · Fy + c7 · Fz + d7 · Mx + e7 · My + g7 · Mz + h7 · P
---- (2)
As described above, the strain outputs t1, t2, t3, t4, and t5 measured by changing the longitudinal force Fx, lateral force Fy, vertical load Fz, overturning moment Mx, rolling resistance moment My, self-aligning torque Mz, and air pressure P in advance. , T6, t7 and coefficients obtained by numerical analysis of data of Fx, Fy, Fz, Mx, My, Mz, and P at that time.

  As described above, the present invention can determine the decrease in tire air pressure by comparing the estimated air pressure obtained in the estimating step with a preset reference air pressure.

Also in the estimation step is selected in the region of the sidewall portion using the eight sensor element unit that is spaced in the circumferential direction and eight from the distortion output measured simultaneously by the eight sensor element unit From the seven strain outputs , the tire pressure is determined using a predetermined estimation formula. That is, it is possible to easily and accurately detect the tire air pressure without using the air pressure sensor, and it is possible to suppress a decrease in weight balance and an increase in weight due to the air pressure sensor. In addition, a sensor element unit for detecting, for example, three translational direction forces (Fx, Fy, Fz) that are useful in the vehicle control system can be used, which can greatly contribute to cost reduction.

  In the present invention, it is possible to estimate all six component forces including three translational direction forces (Fx, Fy, Fz) in addition to the air pressure P using the estimation formula. If so, there is no particular restriction on the estimation of other 6-component forces.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing a pneumatic tire used in the tire pressure drop detecting method of the present invention.

  In FIG. 1, a pneumatic tire 1 includes a carcass 6 that extends from a tread portion 2 through a sidewall portion 3 to a bead core 5 of a bead portion 4, an inner side of the tread portion 2, and a radial direction of the carcass 6. A belt layer 7 disposed on the outside.

  The carcass 6 is formed of one or more, in this example, one carcass ply 6A in which carcass cords are arranged at an angle of, for example, 70 to 90 ° with respect to the tire circumferential direction. The carcass ply 6 </ b> A includes a series of ply folding portions 6 b that are folded from the inner side to the outer side in the tire axial direction around the bead core 5 on both sides of the ply main body portion 6 a that extends between the bead cores 5 and 5. Further, a bead apex rubber 8 for bead reinforcement having a triangular cross section extending outward from the bead core 5 in the tire radial direction is disposed between the ply main body portion 6a and the ply turn-up portion 6b.

  The belt layer 7 is formed from two or more belt plies 7A and 7B in which belt cords are arranged at an angle of, for example, 10 to 35 ° with respect to the tire circumferential direction, and each belt cord is between plies. By crossing each other, the belt rigidity is enhanced, and the substantially entire width of the tread portion 2 is firmly reinforced with a tagging effect. In this example, a band layer 9 in which band cords are arranged at an angle of 5 degrees or less with respect to the circumferential direction is provided on the outer side in the radial direction of the belt layer 7 in order to improve high-speed running performance and high-speed durability. Provided.

In the tire 1 of this embodiment, a strain sensor 10 that detects the surface strain is provided in the region Y of the sidewall portion 3. The strain sensor 10 is formed of eight sensor element units 20. The sensor element units 20 are not particularly limited as long as they are spaced apart in the circumferential direction, but are preferably arranged on the same circumferential line j around the tire axis, and at this time, equidistant in the tire circumferential direction. It is more preferable from the viewpoint of simplicity of measurement control and the like.

  Further, the region Y of the sidewall portion 3 is a region range that divides a distance L of 25% of the tire cross-sectional height H inward and outward in the radial direction around the intermediate height position M of the tire cross-sectional height H. Preferably, the distance L is set to 20% or even 15% of the tire cross-section height H, and the strain sensor 10 is provided in an area range closer to the intermediate height position M. The tire cross-sectional height H means the height in the radial direction from the bead base line BL to the tread surface on the tire equator.

In this region Y, the tire has 6 elements (longitudinal force Fx, lateral force Fy, vertical load Fz, overturning moment Mx, rolling resistance moment My, self-aligning torque Mz) and air pressure P. The surface strain ε generated when a load is applied to the element is a part having a substantially linear correlation with each element. Accordingly, in this region (region Y), the surface strain εx generated by the longitudinal force Fx can be approximated by a linear function εx = f (Fx) of Fx, and similarly, the surface strain εy generated by the lateral force Fy is A surface strain εz generated by a vertical function Fz with a linear function εy = f (Fy) of Fy is a linear function εz = f (Fz) of Fz, and a surface strain εmx generated by an overturning moment Mx is a linear function of Mx. The surface strain εmy generated by the rolling resistance moment My with the function εmx = f (Mx) is the linear function εmy = f (My) of My, and the surface strain εmz generated by the self-aligning torque Mz is the linear function of Mz. The surface strain εp generated by the air pressure P when εmz = f (Mz) can be approximated by a linear function εp = f (P) of P, respectively. Accordingly, the surface strain ε generated when each element acts can be approximated by the sum of the surface strains εx, εy, εz, εmx, εmy, εmz, εp, that is, the following equation (b ′). .
ε = f (Fx) + f (Fy) + f (Fz) + f (Mx) + f (My) + f (Mz) + f (P)
= A · Fx + b · Fy + c · Fz + d · Mx + e · My + g · Mz + h · P
---- (b ')

  Next, as shown in FIGS. 3 to 5, the sensor element unit 20 is a block shape in which a magnet 11 and a magnetic sensor element 12 facing the magnet 11 with a gap are integrated via an elastic material 13. It is formed as a mold body.

  As the magnetic sensor element 12, a Hall element, an MR element (magnetoresistance effect element), a TMF-MI element, a TMF-FG element, an amorphous sensor, or the like can be adopted. Particularly, the compactness, sensitivity, ease of handling, etc. From the viewpoint, a Hall element can be preferably employed. In the sensor element unit 20, it is important that the sensor element unit 20 can be elastically deformed flexibly following the movement of the sidewall portion 3, and various rubber elastic materials are employed as the elastic member 13. In particular, the thermoplastic elastomer (TPE) can be molded by plastic molding such as cast molding or injection molding, and can be suitably employed from the viewpoint of manufacturing the sensor element unit 20.

  As the sensor element unit 20, as shown in FIGS. 3A and 3B, a 1-1 type formed by one magnet 11 and one magnetic sensor element 12, and FIGS. 1-n type formed by one magnet 11 and plural (n, for example, two) magnetic sensor elements 12, as shown in FIGS. 5A and 5B, and plural (n, For example, an n-1 type formed of two magnets 11 and one magnetic sensor element 12 can be used. In the figure, reference numeral 12 s denotes the sensing part surface 12 s of the magnetic sensor element 12, reference numeral 11 s denotes the magnetic pole face of the magnet 11, and reference numeral N denotes the gain maximum line at which the gain of the sensor element unit 20 is maximum. Yes. In addition, as the sensor element unit 20, a resistance wire strain gauge, a unit using a piezo element, or the like can be employed.

  The sensor element unit 20 inclines the maximum gain line N at an angle θ of 10 to 80 ° with respect to the tire radial direction line, as shown in FIG. Mounted in the direction. Thereby, the measurement accuracy of the surface strain ε by each element can be improved. The angle θ is preferably 20 to 70 °, more preferably 30 to 60 °, and further preferably 40 to 50 °.

  Each sensor element unit 20 incorporates a transmission means for transmitting the measured strain output of the surface strain ε to an electronic control unit (ECU) of a vehicle control system provided in the vehicle. This transmitting means is composed of a semiconductor in which a transmission / reception circuit, a control circuit, a memory, etc. are made into a chip, and an antenna. The distortion output data can be transmitted as response radio waves.

Next, the tire pressure drop detecting method of the present invention will be described using the pneumatic tire 1. The method for detecting a decrease in air pressure includes an estimation step and a determination step. In the estimation step, by selecting seven strain outputs from the eight strain outputs simultaneously measured by the eight sensor element units 20, eight strain output combinations including seven strain outputs are created, When the seven distortion outputs in the distortion output combination are defined as t1 to t7 , for each distortion output combination, the seven distortion outputs t1 to t7 are applied to the following estimation equation (1) to obtain each distortion output. The air pressure P for each combination is obtained. Further, in the determination step, a decrease in tire air pressure is determined by comparing an average air pressure obtained by averaging a total of eight estimated air pressures P obtained in the estimation step with a preset reference air pressure.

  Here, as described above, the relationship between the tire surface strain ε and the elements Fx, Fy, Fz, Mx, My, Mz, and P acting at that time is represented by the formula (b ′) described above. It seems to have done. And in order to derive each element Fx, Fy, Fz, Mx, My, Mz, P from the surface strain ε measurable by the sensor element unit 20, Fx, Fy, Fz, Mx, My, Mz, P are unknown numbers. It can be achieved by solving the seven-element linear equation which is the equation (b ′). However, in order to solve this 7-element linear equation, seven simultaneous equations are required.

Therefore, in the detection method of the present invention, eight sensor element units 20 are arranged in the circumferential direction in the region Y of the sidewall portion 3, and seven of the sensor element units 20a, 20b, 20c, 20d, and 20e are included. , 20 g, by Ri When t1~t7 distortion output detected simultaneously in 20h, on the basis of the formula (b '), can be obtained following seven simultaneous equation (2). In the formulas, a1 to a7, b1 to b7, c1 to c7, d1 to d7, e1 to e7, g1 to g7, and h1 to h7 are coefficients.
t1 = a1 · Fx + b1 · Fy + c1 · Fz + d1 · Mx + e1 · My + g1 · Mz + h1 · P
t2 = a2, Fx + b2, Fy + c2, Fz + d2, Mx + e2, My + g2, Mz + h2, P
t3 = a3 · Fx + b3 · Fy + c3 · Fz + d3 · Mx + e3 · My + g3 · Mz + h3 · P
t4 = a4 · Fx + b4 · Fy + c4 · Fz + d4 · Mx + e4 · My + g4 · Mz + h4 · P
t5 = a5 · Fx + b5 · Fy + c5 · Fz + d5 · Mx + e5 · My + g5 · Mz + h5 · P
t6 = a6 · Fx + b6 · Fy + c6 · Fz + d6 · Mx + e6 · My + g6 · Mz + h6 · P
t7 = a7 · Fx + b7 · Fy + c7 · Fz + d7 · Mx + e7 · My + g7 · Mz + h7 · P
---- (2)

From these seven simultaneous equations, the following estimation equation (1), which is a determinant for obtaining each element Fx, Fy, Fz, Mx, My, Mz, and P, can be obtained.
┌Fx┐ ┌a1 b1 c1 d1 e1 g1 h1┐-1 ┌t1┐
│Fy│ │a2 b2 c2 d2 e2 g2 h2│ │t2│
│Fz│ │a3 b3 c3 d3 e3 g3 h3│ │t3│
│Mx│ = │a4 b4 c4 d4 e4 g4 h4│ │t4│
│My│ │a5 b5 c5 d5 e5 g5 h5│ │t5│
│Mz│ │a6 b6 c6 d6 e6 g6 h6│ │t6│
└P ┘ 7a7 b7 c7 d7 e7 g7 h7┘ └t7┘
---- (1)

Therefore , by substituting the strain outputs t1 to t7 of the surface strain ε measured simultaneously by the predetermined seven sensor element units 20a to 20h into the estimation equation (1), each element Fx, Fy, Fz, Mx, My, Mz, and P can be obtained respectively.

  The coefficients a1 to a7, b1 to b7, c1 to c7, d1 to d7, e1 to e7, g1 to g7, and h1 to h7 are determined by the respective elements Fx, Fy, Fz, Mx, My in the prior load application test. , Mz, and P are changed, and the measured distortion outputs t1 to t7 and the element values Fx, Fy, Fz, Mx, My, Mz, and P at that time are numerically analyzed using, for example, a computer Can be obtained.

  Here, the coefficients a1 to a7, b1 to b7, c1 to c7, d1 to d7, e1 to e7, g1 to g7, h1 to h7 are coefficients specific to the rotation angle position determined for each rotation angle position of the tire. is there. Accordingly, the rotational angle positions of the seven sensor element units 20a to 20h when performing a prior load application test and the seven sensor element units when detecting the elements Fx, Fy, Fz, Mx, My, Mz, and P. Both the rotational angle positions 20a to 20h need to be the same position. Therefore, when detecting each element Fx, Fy, Fz, Mx, My, Mz, and P in a running tire that actually rotates, for example, an encoder that detects the tire rotation angle position on the tire, wheel, axle, etc. It is necessary to output the distortion outputs t1 to t7 for each predetermined rotation angle position detected by the rotation position detector.

FIG. 2 illustrates a case where eight sensor element units 20a to 20i are arranged in the circumferential direction in the region Y of the sidewall portion 3 with a central angle α of 45 °, and this is taken as an example. This will be specifically described below. First, for example, by setting polar coordinates (the tire counter-rotating direction is +) with the ground contact center point as the origin O (0 °) around the tire axis, for example, 0 ° positions J0, 45 around the tire axis. Eight rotation angle positions J of a position J1, a 90 degree position J2, a 135 degree position J3, a 180 degree position J4, a 225 degree position J5, a 270 degree position J6, and a 315 degree position J7 can be provided at equiangular pitches .

In the tire rotation, the eight sensor elements unit 20a~20i passes through the eight rotational angular position J0～J 7 simultaneously. Thus, by measuring the surface strain ε by the sensor element unit when passing through the rotational angular position J0～J 7, it is possible to measure the surface strain ε at a particular rotational angle position J0～J 7 simultaneously.

  In this example, since the eight sensor element units are arranged at an equiangular pitch of 45 °, each time the tire rotates 45 °, the surface strain ε is measured and each element Fx, Fy, Fz, Mx is measured. , My, Mz, and P can be detected, but when the tires are arranged at unequal angle pitches, the surface strain ε can be measured every time the tire rotates once (360 °).

In the estimation step, as described above, by selecting seven strain outputs from the eight strain outputs measured simultaneously, eight strain output combinations including seven strain outputs are created, and each strain output When the seven strain outputs in the combination are t1 to t7, for each strain output combination, the seven strain outputs t1 to t7 and the estimation formula (1) are used to calculate the tire strain for each strain output combination . The air pressure P is calculated and obtained.

Next, in the determination step, a decrease in tire air pressure is determined by comparing an average air pressure obtained by averaging a total of eight estimated air pressures P obtained in the estimation step with a preset reference air pressure Pp. The reference air pressure Pp is preferably set to an internal pressure that needs to call the driver's attention, for example, a pressure in the range of 80 to 70% of the normal internal pressure. The “regular internal pressure” is the air pressure determined by the standard for each tire. The maximum air pressure in the case of JATMA, the maximum value described in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the case of TRA, ETRTO means "INFLATION PRESSURE".

In the determination step, the average air pressure is compared with the reference air pressure Pp. If the average air pressure is smaller than the reference air pressure , it is determined that the air pressure has decreased, and the driver can detect the air pressure by an alarm means such as a pilot lamp or a buzzer. Call attention to the decline. In addition, from the viewpoint of preventing malfunction, it is preferable that the determination be made that the air pressure has decreased when the low pressure result of average air pressure < reference air pressure continues two or more times.

  Note that the tire air pressure does not change abruptly as compared with the other 6 component forces. Therefore, in the air pressure drop detection method of the present embodiment, it is not necessary to calculate the air pressure P every time the tire surface strain is measured. For example, the air pressure P can be calculated at a predetermined time interval such as every 10 seconds. It is preferable in order to reduce the load.

  As mentioned above, although especially preferable embodiment of this invention was explained in full detail, this invention is not limited to embodiment of illustration, It can deform | transform and implement in a various aspect.

  In order to confirm the effect of the present invention, a pneumatic tire (size 225 / 55R17) in which a strain sensor is provided in the region of the sidewall portion was manufactured in accordance with the specifications shown in Table 1. Each tire uses a sensor element unit in which a magnet and a hall element are integrated with a rubber elastic material, and the angle θ of the maximum gain line is 45 ° and is arranged at equal intervals on the same circumferential line. doing.

Then, based on the strain output of the surface strain ε measured by the strain sensor, the longitudinal force Fx and the air pressure P of the six component forces are calculated from the estimation formula, and the calculated value (detected value) is calculated from the measured value. Were compared, and the detection accuracy was evaluated in the following four stages of x, Δ, ○, and ◎. In Comparative Examples 1 and 2, the following estimation formula (3) is used based on Patent Document 1, and in Comparative Example 3 and Example 1 , the estimation formula (1) is used.
┌Fx┐ ┌a1 b1 c1┐-1 ┌t1┐
│Fy│ = │a2 b2 c2│ │t2│
└Fz┘ └a3 b3 c3┘ └t3┘
---- (3)
X --- calculation is difficult Δ --- the error of the calculated value is greater than 20% and less than 50% of the measured value;
○ --- The error of the calculated value is greater than 10% and less than 20% of the measured value;
◎ --- The error of the calculated value is within 10% of the measured value;

In the case of Example 1, seven data are selected from eight data. At this time, eight combinations are possible. For each combination, the air pressure P is calculated using seven data, and the average value is adopted. In this case, even when a measurement error occurs in one strain sensor due to electrical noise or the like, the influence can be reduced, and detection accuracy and reliability can be improved.

It is sectional drawing which shows the pneumatic tire used for the air pressure fall detection method of this invention. It is a side view of the pneumatic tire which shows the arrangement state of a sensor element unit schematically. (A), (B) is the top view and perspective view which show one Example of a sensor element unit. (A), (B) is the top view and perspective view which show the other Example of a sensor element unit. (A), (B) is the top view and perspective view which show other Example of a sensor element unit. It is a diagram which shows the attachment direction of a sensor element unit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tire 3 Side wall part 10 Strain sensor 11 Magnet 12 Magnetic sensor element 13 Elastic material 20 Sensor element unit J Rotation angle position N Gain maximum line Pp Reference | standard air pressure Y area | region

Claims (1)

A tire pressure drop detection method for detecting a tire pressure drop by a strain output of a strain sensor attached to a tire and measuring a tire surface strain,
It said strain sensor comprises eight sensor element unit that is spaced circumferentially in the region of the sidewall portion, and eight from the simultaneously measured eight strain output by the sensor element unit of seven distortion output By selecting, creating eight different distortion output combinations consisting of seven distortion outputs,
When the seven distortion outputs in each distortion output combination are defined as t1 to t7, the seven distortion outputs t1 to t7 are applied to the following estimation equation (1) for each distortion output combination , An estimation step for obtaining a tire pressure P for each output combination ;
And a determination step for determining a decrease in tire air pressure by comparing an average air pressure obtained by averaging a total of eight estimated air pressures P obtained in the estimation step with a preset reference air pressure,
The sensor element unit has a built-in transmission means for transmitting the measured distortion output to the electronic control device on the vehicle side, and the transmission means includes a semiconductor in which a transmission / reception circuit, a control circuit, and a memory are chipped, an antenna, When the interrogation radio wave is received from the vehicle-side electronic control device, it can be used as electrical energy and the distortion output data in the memory can be transmitted as a response radio wave. Method.
┌Fx┐ ┌a1 b1 c1 d1 e1 g1 h1┐-1 ┌t1┐
│Fy│ │a2 b2 c2 d2 e2 g2 h2│ │t2│
│Fz│ │a3 b3 c3 d3 e3 g3 h3│ │t3│
│Mx│ = │a4 b4 c4 d4 e4 g4 h4│ │t4│
│My│ │a5 b5 c5 d5 e5 g5 h5│ │t5│
│Mz│ │a6 b6 c6 d6 e6 g6 h6│ │t6│
└P ┘ 7a7 b7 c7 d7 e7 g7 h7┘ └t7┘
---- (1)
The symbols a1 to a7, b1 to b7, c1 to c7, d1 to d7, e1 to e7, g1 to g7, and h1 to h7 in the estimation formula (1) are coefficients,
t1 = a1 · Fx + b1 · Fy + c1 · Fz + d1 · Mx + e1 · My + g1 · Mz + h1 · P
t2 = a2, Fx + b2, Fy + c2, Fz + d2, Mx + e2, My + g2, Mz + h2, P
t3 = a3 · Fx + b3 · Fy + c3 · Fz + d3 · Mx + e3 · My + g3 · Mz + h3 · P
t4 = a4 · Fx + b4 · Fy + c4 · Fz + d4 · Mx + e4 · My + g4 · Mz + h4 · P
t5 = a5 · Fx + b5 · Fy + c5 · Fz + d5 · Mx + e5 · My + g5 · Mz + h5 · P
t6 = a6 · Fx + b6 · Fy + c6 · Fz + d6 · Mx + e6 · My + g6 · Mz + h6 · P
t7 = a7 · Fx + b7 · Fy + c7 · Fz + d7 · Mx + e7 · My + g7 · Mz + h7 · P
---- (2)
As described above, the strain outputs t1, t2, t3, t4, and t5 measured by changing the longitudinal force Fx, lateral force Fy, vertical load Fz, overturning moment Mx, rolling resistance moment My, self-aligning torque Mz, and air pressure P in advance. , T6, t7 and coefficients obtained by numerical analysis of data of Fx, Fy, Fz, Mx, My, Mz, and P at that time.

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