JP3948678B2 - Wheel turning stability evaluation method and wheel turning stability evaluation apparatus - Google Patents

Description

  The present invention relates to a wheel turning stability evaluation method for determining whether or not there is a risk that a wheel is in a slip state during turning of the vehicle, and turning of the wheel. The present invention relates to a stability evaluation apparatus.

  The turning characteristics (cornering characteristics) of automobile vehicles are particularly important for the handling stability of automobile vehicles, and the cornering characteristics of automobile vehicles are also important for the design of automobile vehicles and wheels that have higher handling stability. Evaluation is important. It is known that the cornering force applied to the vehicle wheel and the slip angle of the wheel during the turn are deeply related to the turning characteristic of the vehicle.

  In cornering of automobile vehicles, the sum of forces (cornering forces) generated on the ground contact surfaces of the front and rear tires is balanced with the centrifugal force of the vehicle. When this balanced state collapses and the centrifugal force of the vehicle increases with respect to the cornering force, the wheel slides greatly to a slip state. In the present specification, the slip state refers to a state in which the wheel slides greatly to such an extent that the stability of vehicle operation by the driver of the vehicle is significantly reduced. The cornering characteristics of an automobile equipped with wheels with tires mounted on the wheels are related to various factors such as the characteristics of the vehicle structure (weight balance, etc.), suspension characteristics, tire characteristics, and road surface conditions. ing. For this reason, the running conditions (slip conditions) that cause the wheels to slip sideways and become slipped vary depending on the vehicle, tires, and the like. Knowing the turning stability of a wheel under various driving conditions (the margin until the wheel reaches a side-slip state (the safety margin until the wheel enters a slip state)) as a turning characteristic of an automobile vehicle is higher steering stability. It is important for the design of motor vehicles and wheels that have the characteristics.

  For example, as a method for evaluating the cornering force generated in a specific tire, a method using a known indoor cornering tester (for example, a drum type tester or a flat belt tester) can be mentioned. In such an indoor cornering tester, for example, the specific tire is brought into contact with the simulated road surface while a load is applied to the specific tire. Then, the virtual road surface and the specific tire are relatively moved to roll the specific tire, and the cornering force generated on the contact surface of the specific tire is measured.

  However, as described above, there are various cornering forces generated on tires actually mounted on the vehicle, such as vehicle structure characteristics (weight balance, etc.), suspension characteristics, tire characteristics, and road surface conditions. Factors are involved. Further, while the vehicle is actually traveling, a change in load applied to each wheel frequently occurs due to a change in the posture of the vehicle. For example, in a known indoor cornering tester, a tire is actually attached to a vehicle, and a state when the vehicle actually travels on a road surface (a load state applied to the tire or a rolling state of the tire) is reproduced. The reproduction accuracy is limited, and the cornering force generated on the contact surface of the specific tire when the specific tire is actually attached to the vehicle cannot be accurately measured.

On the other hand, Patent Document 1 describes a system for predicting the force of a tire as a method for evaluating a cornering force generated in a tire actually mounted on a vehicle. In the system described in Patent Document 1, the torsional deformation of the tire sidewall is measured by a sensor, and the cornering force generated in the tire is estimated from the measured torsional deformation. Patent Document 2 below discloses a vehicle state estimation device that sets a tire model corresponding to a motion state of a vehicle during traveling of the vehicle and estimates the traveling state of the vehicle based on the tire model. Patent Document 2 describes that by using the vehicle state estimation device described in Patent Document 2, it is possible to always accurately estimate the travel state of the vehicle while the vehicle is traveling.
Special table 2004-512207 gazette Japanese Patent Laid-Open No. 8-198131

  However, in the system described in Patent Document 1, it is necessary to grasp the relationship between the tire deformation and the force generated during the deformation in advance. However, it takes a lot of labor to grasp the relationship between the tire deformation and the force generated during the deformation. In addition, only by using the relationship between the tire deformation and the force generated in the deformation, which has been grasped in advance, various states when the vehicle actually travels on the road surface (the load state applied to the tire, Regarding the rolling state), the lateral force generated on the ground contact surface of the tire cannot be accurately measured.

  Moreover, in the apparatus described in Patent Document 2, it is necessary to set a tire model as detailed as possible before actually estimating the traveling state of the vehicle. For this reason, before actually estimating the running state of the vehicle, it is necessary to execute a characteristic curve identification routine for identifying a characteristic curve for the wheel load, a tire model setting routine for setting a tire model, and the like. In these routines, it is necessary to acquire a huge amount of data and execute arithmetic processing, and there is a problem that time and cost for evaluation are remarkably large.

  Further, in order to evaluate the turning stability of the wheel (margin until reaching a slip state) under traveling conditions in which the tire may slip, it is necessary to predict the vehicle behavior in as short a time as possible. However, in the vehicle state estimation device described in Patent Document 2, the slip angle of the wheel is calculated from the detection result by a steering angle sensor, an acceleration sensor, a yaw rate sensor or the like mounted on the vehicle, and an analysis process using a tire model is performed. carry out. Such complicated processing takes time, and calculation / analysis processing cannot be preceded with respect to the behavior of the vehicle. In the vehicle state estimation device described in Patent Document 2, it is difficult to evaluate the turning stability of the wheel (margin until reaching the slip state) while actually turning the vehicle.

  Accordingly, the present invention can evaluate the turning stability of a wheel under various driving conditions (margin until reaching a slip state) while actually turning the vehicle, An object of the present invention is to provide a wheel turning stability evaluation device.

In order to solve the above-mentioned problems, the present invention provides a method for evaluating the turning stability of a wheel when a vehicle including wheels on which tires are mounted is turning on a road surface. From the front contact end of the tire to the rear end of the ground, the amount of displacement of the predetermined portion of the tire in the lateral direction of the tire due to the lateral deformation of the outer periphery of the tire when turning A step of continuously deriving the integrated value for each unit time, and whenever the integrated value of the displacement amount is derived, the integrated value of the derived displacement amount and the displacement amount derived one time before A first calculation step of repeatedly calculating a change amount per unit time of the integrated value of the displacement amount as a change rate of tire deformation from the integrated value of each time, and whenever a change rate of the tire deformation is calculated, Calculated tire deformation Based on the variation rate calculated in the second calculation step, a second calculation step of calculating a variation rate of the calculated change rate of the tire deformation with respect to the reference value using the rate of change as a reference value, And a step of determining the turning stability of the wheel, which represents a margin until the wheel reaches a side-sliding state.

In the deriving step, acceleration data in the tire width direction of the predetermined portion of the tire, which is measured by an acceleration sensor installed at a position corresponding to the predetermined portion of the tire, along with the lateral deformation of the tire. It is preferable to derive an integrated value of the displacement amount using. The acceleration sensor is preferably installed on the tire inner peripheral surface facing the tire cavity region of the tread portion of the tire.

Further, when the vehicle is turning, the acceleration data in the tire radial direction of the predetermined portion of the tire and the turning of the vehicle in accordance with the ground deformation of the outer peripheral surface of the tire due to rolling of the tire A data acquisition step of acquiring acceleration data in a tire width direction of a predetermined portion of the tire according to a lateral deformation of the tire on an outer peripheral surface of the tire, and in the step of deriving, the tire Based on the acceleration data in the radial direction, the timing at which the predetermined portion contacts the road surface and the timing at which the predetermined portion moves away from the road surface are obtained, and the second floor time integration is performed on the acceleration data in the tire width direction. Thus, a time system of the lateral displacement amount of the tire at a predetermined portion of the tire due to the lateral deformation of the tire. Data is obtained, and the integrated value of the displacement amount is derived by integrating the time series data of the displacement amount from the timing at which the predetermined portion contacts the road surface to the timing at which the predetermined portion separates from the road surface. It is preferable.

Further, in the deriving step, two timings at which the acceleration data in the tire radial direction of the predetermined portion of the tire crosses zero in accordance with the deformation of the outer peripheral surface of the tire are obtained, and the two timings are grounded. It is preferable to set the timing and the timing of separation.

In the second calculation step, it is preferable that the change rate is calculated using the change rate of the tire deformation first calculated after the vehicle starts turning as the reference value.

In the determination step, the variation ratio calculated in the second calculation step is compared with a predetermined threshold value, and when the value of the variation ratio falls below the threshold value, the wheel is in a slipping state. It is preferable to determine that the risk of reaching is high.

The present invention is also a device for evaluating the turning stability of a wheel when a vehicle including a wheel equipped with a tire is turning on a road surface, and capable of storing numerical information; When the vehicle is turning, the amount of lateral displacement of the tire at a predetermined portion of the tire caused by lateral deformation of the tire on the outer peripheral surface of the tire is grounded from the front end of the tire. The integrated value up to the rear end is continuously derived every unit time, and the deriving unit for storing in the memory and the integrated value of the displacement amount are derived each time the integrated value of the displacement amount is derived. And receiving the previous integrated value of the displacement amount stored in the memory, and deriving the integrated value of the displacement amount and the integrated value of the displacement amount stored previously. From the above, the accumulated displacement amount A first calculation unit that repeatedly calculates the amount of change per unit time as a rate of change in tire deformation, and receives the calculated rate of change in tire deformation each time the rate of change in tire deformation is calculated, Using the calculated change rate of the tire deformation as a reference value, a second calculation unit that repeatedly calculates a variation ratio of the calculated change rate of the tire deformation with respect to the reference value, and the second calculation unit A determination unit that receives the fluctuation rate of the rate of change of the tire deformation and determines the turning stability of the wheel that represents a margin until the wheel reaches a side slip state based on the fluctuation rate. A wheel turning stability evaluation device is also provided.

  In addition, it has a detection means for detecting that the vehicle has started turning while the vehicle is running, and the first calculation unit calculates the first time after the detection means detects the start of turning of the vehicle. The tire deformation change rate is stored in the memory as the reference value, and the second calculation unit reads the reference value from the memory every time the tire deformation change rate is calculated. It is preferable to calculate the fluctuation ratio.

  In addition, the determination unit compares the variation ratio calculated by the second calculation unit with a predetermined threshold value, and when the value of the variation ratio falls below the threshold value, the wheel is in a skidding state. It is preferable to determine that the risk of reaching is high.

  According to the wheel turning stability evaluation method and the wheel turning stability evaluation device of the present invention, the turning stability of the wheel (until the slip state is reached) when the vehicle is actually turned under various driving conditions. Margin) can be evaluated. According to the present invention, the turning stability of a wheel is evaluated in consideration of various factors such as actual vehicle structure characteristics (weight balance, etc.), suspension characteristics, tire characteristics, and road surface conditions. be able to. Further, the turning stability can be evaluated in a short time without calculating the slip angle, cornering force, and the like. For this reason, during the turning of the vehicle, for example, the turning stability of the wheel (the margin until the vehicle enters a slip state) can be notified to the driver of the vehicle in real time. Moreover, the turning stability performance inherent to the tire can be evaluated in a short time without requiring an expensive device or a large amount of labor.

  Hereinafter, the wheel turning stability evaluation method and the wheel turning stability evaluation apparatus of the present invention will be described in detail based on the preferred embodiments shown in the accompanying drawings.

  FIG. 1 is a schematic configuration diagram illustrating a wheel turning stability evaluation device 10 (device 10) which is an example of a wheel turning stability evaluation device of the present invention. The device 10 is provided in a vehicle 12 provided with four wheels 14a to 14d, and is a device for determining in real time the turning stability of each of the wheels 14a to 14d while the vehicle 12 is turning. These four wheels 14a to 14d are wheels formed by mounting the same type of tires (tires having the same tire size, tire rim width, belt structure, tire filling air pressure, etc.) 15a to 15d, respectively. is there. The apparatus 10 includes sensor units 16a to 16d, a turning start detection unit 18, a data processing unit 20, and a display 40.

  The sensor units 16a to 16d are respectively provided on the four wheels 14a to 14d, and are generated when the tires 15a to 15d of the wheels receive external force from the road surface when the vehicle 12 travels on the road surface. The acceleration information of 15 predetermined parts is acquired and continuously transmitted by a radio signal. The turning start detection means 18 detects that the vehicle 12 has started turning, and sends a detection result notifying the start of turning to the data processing unit 20. The turning start detection means 18 may be configured to include a rotation angle sensor attached to a steering shaft or the like, for example. In this case, for example, the rotation angle sensor measures the rotation angle of the steering shaft, derives the steering angle of the wheels 14a to 14d arranged in the vehicle 12 based on the measurement result, and determines the vehicle based on the steering angle. 12 detects that the vehicle has started turning. For example, when the steering angle is equal to or greater than a predetermined reference steering angle, it may be determined that the vehicle has started turning. Further, the turning start detection means 18 may be configured to include a rotational angular velocity sensor attached to, for example, a steering shaft. In this case, for example, when the rotational angular velocity is equal to or higher than a predetermined reference angular velocity, it may be determined that the cornering has started. Moreover, the turning start detection means 18 may be configured to include, for example, a well-known GPS (Global Positioning System) and a database that stores data of a traveling path on which the vehicle 12 travels. This database stores in detail the position of a corner portion (portion where the turning radius is smaller than a predetermined value) on the road on which the vehicle 12 travels. For example, information on the current position of the vehicle 12 and information on the traveling direction may be acquired by GPS, and the timing at which the vehicle 12 reaches the corner portion may be detected as the timing at which the turning travel starts. The detection result by the turning start detection means 18 is sent to the data processing unit 20.

  When the data processing unit 20 detects that the vehicle 12 has started turning by means of the measurement data by the turning start detection means 18, the data processing unit 20 starts receiving acceleration information transmitted from the sensor units 16a to 16d, and this acceleration information. And the turning stability of each wheel during turning is determined in real time. The display 40 displays processing results and determination results in the data processing unit 20. In the example shown in FIG. 1, the data processing unit 20 is disposed on the vehicle 12, but the data processing unit 20 is portable and is not limited to being disposed on the vehicle 12. Hereinafter, these sensor unit, data processing unit, and display will be described in detail.

  FIG. 2 is a schematic configuration diagram illustrating the sensor unit 16 (representing the sensor units 16a to 16d) and the data processing unit 20 in the apparatus 10 illustrated in FIG. The wheels 14a to 14d and the sensor units 16a to 16d have the same configuration. The sensor unit 16 includes an acceleration sensor 2 and a transmitter 17.

  FIGS. 3A and 3B are diagrams for explaining the installation position of the acceleration sensor 2 in the tire 15 of the wheel 14 (represented by the tires 15a to 15d) and the acceleration data detected by the acceleration sensor 2. FIG. is there. FIG. 3A is a perspective view of the wheel 14 as viewed from the grounded road surface side, and shows a state where the tire 15 is observed through the grounded road surface when the grounded road surface is a transparent plate. . FIG. 3B shows an enlarged part of a cross-sectional view when the tire 15 is cut along a meridional section including the acceleration sensor 2 (a plane perpendicular to the tire equatorial plane). FIGS. 3A and 3B schematically show a state in which the vehicle 12 is traveling straight ahead.

  As shown in FIG. 3B, the acceleration sensor 2 is installed at the inner surface position 11 of the tread portion of the tire 15. The acceleration sensor 2 is an acceleration sensor that can measure accelerations in three orthogonal directions with reference to the tire inner surface position 11 on which the acceleration sensor 2 is provided. In this embodiment, the tire circumference along the tire width direction (tire lateral direction) acceleration, the tire radial direction acceleration, and the tire outer peripheral shape shown in FIG. Measure the acceleration in each direction. It can be said that the inner surface position 11 of the tire 15 and the outer surface position 13 of the tire 15 corresponding to the inner surface position 11 are very close, and the acceleration of the inner surface position 11 corresponds to the acceleration of the outer surface position 13.

  As the acceleration sensor 2, for example, a semiconductor acceleration sensor disclosed in Japanese Patent Application No. 2003-134727 filed earlier by the applicant of the present application is exemplified. Specifically, the semiconductor acceleration sensor includes a Si wafer having a diaphragm formed in the outer peripheral frame portion of the Si wafer, and a pedestal for fixing the outer peripheral frame portion, and a weight is provided at the center of one surface of the diaphragm. And a plurality of piezoresistors are formed on the diaphragm. When acceleration is applied to the semiconductor acceleration sensor, the diaphragm is deformed, and the resistance value of the piezoresistor changes due to the deformation. A bridge circuit is formed so that this change can be detected as acceleration information. The acceleration sensor 2 is fixed at the tire inner surface position 11 so that acceleration in the tire radial direction, tire width direction, and tire circumferential direction can be measured, thereby measuring acceleration acting on the tread portion during tire rotation. can do.

  More specifically, the acceleration sensor 2 is fixed to the tire inner surface position 11 so that the tire radial direction, the tire width direction, and the tire circumferential direction can be measured. Here, the tire radial direction refers to the rotation of the tire 15 from the tire inner surface position 11 in a state where the internal cavity region of the tire 15 is filled with air so that the tire 15 has a prescribed air pressure and the tire 15 is not grounded. It is the direction along the perpendicular line down to the central axis. Further, the tire width direction is a direction parallel to a plane (a meridian section of the tire 15) that is perpendicular to the tire radial direction and passes through the tire inner surface position 11 and includes the rotation center axis of the tire 15. The tire circumferential direction is a direction perpendicular to both the tire radial direction and the tire width direction. In addition to this, the acceleration sensor 2 may be an acceleration pickup using a piezoelectric element, or a strain gauge type acceleration pickup combined with a strain gauge.

  The acceleration detected by the acceleration sensor 2 is sent from the transmitter 17 of each transmission unit to the data processing unit 20. Note that the transmitter 17 may not be provided, and for example, the acceleration sensor 2 may be separately provided with a transmission function and may be configured to transmit from the acceleration sensor 2 to the data processing unit 20. The transmitters 17 provided on the wheels 14 each have identification information (ID) that can identify each of the transmitters 17. The transmitter 17 has an ID together with the acceleration measurement data measured by the corresponding acceleration sensor. Send.

  The data processing unit 20 includes a CPU 23, a memory 27, a receiver 3, an amplifier 4, a processing unit 21, and a determination unit 30. The acceleration information transmitted from the transmitter 17 is received by the receiver 3 of the data processing unit 20, amplified by the amplifier 4, and sent to the processing means 21. The data processing unit 20 is a computer in which the units shown in the processing unit 21 and the determination unit 30 function by the CPU 23 executing a program stored in the memory 27. In addition, each part of the process means 21 and the determination means 30 may each be comprised by the exclusive circuit.

  The processing means 21 includes an acceleration data acquisition unit 22, a signal processing unit 24, a contact timing deriving unit 26, and a locus deriving unit 28. The data acquisition unit 22 is a part that acquires, as input data, acceleration measurement data amplified by the amplifier 4 in the tire radial direction, the tire width direction, and the tire circumferential direction. The data supplied from the amplifier 4 is analog data, and the tire acceleration data acquisition unit 22 samples the acceleration data in each of the three directions at a predetermined sampling frequency and converts them into digital data. In addition, the data acquisition part 22 is the measurement data of the acceleration of the tire of which wheel the measurement data of the acceleration transmitted from each wheel based on the above-mentioned ID transmitted from each transmitter 17 (wheels 14a to 14). Which wheel of the wheels 14d is determined). Thereafter, each processing performed by the signal processing unit 24, the contact timing deriving unit 26 and the trajectory deriving unit 28, and the determination unit 30 described later is performed in parallel on the measurement data of the tires of the respective wheels.

  The signal processing unit 24 is a part that extracts time-series data of acceleration caused by tire deformation from acceleration data of digitized tire radial direction, tire width direction, and tire circumferential direction acceleration data. The signal processing unit 24 performs a smoothing process on these acceleration measurement data, calculates an approximate curve for the smoothed signal, and obtains the background component 1. Then, by removing the background component 1 from the smoothed acceleration measurement data, acceleration time series data (deformation acceleration) in the tire radial direction, the tire width direction, and the tire circumferential direction, respectively. Time-series data). The extracted deformation acceleration time-series data is sent to the contact timing deriving unit 26 and the locus deriving unit 28, respectively. Specific processing in the signal processing unit 24 will be described later.

  The ground contact timing deriving unit 26 is based on the time series data of the deformation acceleration in the tire radial direction, in particular, the timing at which the outer surface position 13 of the tire 15 rolling on the traveling road surface contacts the traveling road surface, and the outer surface position 13 is grounded. The timing away from the road surface is derived. Further, the trajectory deriving unit 28 shows the outer surface position 13 of the tire 15 rolling on the traveling road surface based on the deformation acceleration time-series data in the tire radial direction, the tire width direction, and the tire circumferential direction, as shown in FIG. The trajectory in the XYZ space shown in FIG. The X axis (X direction) in FIG. 3A is an axis (direction) parallel to the ground (the ground contact surface of the tire 15) and parallel to the traveling direction of the tire 15. Further, the Y axis (Y direction) in FIG. 3A is an axis (direction) parallel to the ground and along the rotation center axis of the tire 15. Further, the Z axis (Z direction) in FIG. 3A is an axis (direction) perpendicular to the ground.

  Here, the grounding timing derived by the grounding timing deriving unit 26 and the locus of the outer surface position 13 derived by the locus deriving unit 28 will be described. 4 (a) and 4 (b) are diagrams showing a deformed state of the tire 15 while the vehicle 12 is turning. FIG. 4A is a side view of the tire 15 and shows an enlarged vicinity of the ground contact area between the tire 15 and the road surface. FIG. 4B is a bottom view of the tire 15 as viewed from the ground road surface side, and shows only the ground contact area between the outer peripheral surface of the tire 15 and the road surface.

  As shown in FIG. 4A, the tire 15 of the wheel 14 is pressed against the ground road surface by the weight of the vehicle 12 or the wheel 14 itself. When the tire 15 is viewed from the side, the outer surface of the tire 15 is linear in the ground contact region, and is arcuate in other portions. The outer surface position 13 corresponding to the acceleration sensor 2 installed on the tire 15 contacts the traveling road surface at the front end of the ground contact area, moves along the ground contact surface, and moves away from the travel road surface at the rear end of the ground contact area. In particular, the contact timing deriving unit 26 derives the contact and separation timings of the outer surface position 13 based on the deformation acceleration time series data in the tire radial direction.

  While the vehicle 12 is turning, the equator plane of the tire 15 has an angle (slip angle SA) with respect to the traveling direction of the vehicle 12. That is, the wheels 14 roll while sliding sideways with the equator plane of the tire 15 maintaining the slip angle SA with respect to the traveling direction of the vehicle 12. While the tire 15 is turning, when the ground contact portion is viewed from the coordinate system fixed to the tire 15, the road surface is moving backward. The tread surface of the tire is in contact with the road surface at the front end of the contact portion, and moves to the side rear (downward in FIG. 4B) while maintaining contact (adhesion) with the road surface as time passes. In such a state, the tread surface of the tire 15 is pushed laterally by the road surface, and the tread portion undergoes shear deformation, thereby generating a cornering force substantially perpendicular to the vehicle traveling direction. The amount of shear deformation increases as the tread moves to the rear, and slips at the point where the deformation force is equal to the friction force between the tread and the road surface. At the rear of this equal point, the tread causes a side slip, and a sliding friction force is generated. Then, the tread returns to the original state at the rear end of the grounding portion. The amount of deformation of the shape of the tread portion of the tire strongly affects the size of the cornering force. In the tire in such a rolling state, the outer surface position 13 (the inner surface position 11 and the acceleration sensor 2) has a trajectory as indicated by a thick line in FIG.

  The trajectory deriving unit 28 integrates the deformation acceleration time-series data with respect to time, and calculates the displacement (deformation displacement) based on the deformation of the tire at the outer surface position 13 corresponding to the installation position (inner surface position 11) of the acceleration sensor 2. . Thereby, the locus of the outer surface position 13 of the tire 15 that rolls on the traveling road surface in the XYZ space is derived in detail. Processing in the contact timing deriving unit 26 and the locus calculating unit 28 will be described in detail later.

  Information on the contact timing derived by the contact timing deriving unit 26 and information on the rotation locus derived by the locus deriving unit 28 are sent to the determination unit 30. The determination unit 30 includes an area derivation unit 32, a first calculation unit (change rate calculation unit) 34, a second calculation unit (variation rate calculation unit) 36, and a determination unit 38.

  The area deriving unit 32 calculates information on the deformation area of the outer peripheral surface of the tire 15 due to turning of the vehicle 12 from the timing of contact and separation of the outer surface position 13 and the locus of the outer surface position 13 in the contact region. The information on the deformation area of the outer peripheral surface of the tire 15 is information indicating the magnitude of the deformation amount of the outer peripheral surface of the tire 15 from the front contact end to the rear contact end of the tire 15. Specifically, the time-series data of the deformation displacement in the tire width direction derived by the trajectory deriving unit 28 is integrated from the contact timing of the outer surface position 13 to the separation timing of the outer surface position 13 derived by the contact timing deriving unit 26. Determine the value. That is, the area deriving unit 32 calculates the integrated value of the deformation displacement corresponding to the area (deformation area) indicated by the oblique lines in FIG. Such a deformation area (integrated value of the displacement amount) can be said to represent the magnitude of deformation of the tire 15 in the ground contact region of the tire 15.

  As described above, the magnitude of deformation of the tire 15 in the ground contact region of the tire 15 strongly influences the magnitude of the cornering force, and the above-described deformation area is a parameter representing the magnitude of the cornering force. . The area deriving unit 32 repeatedly derives such a deformed area every predetermined unit time. The derived deformation area data is stored in the memory 27 and sent to the first calculation unit 34.

  The first calculation unit 34 receives the deformation area data sent from the area deriving unit 32, and uses the received deformation area and the deformation area previously calculated and stored in the memory 27 to change the deformation area. Calculate the rate. Specifically, when the first calculation unit 34 receives the current deformation area from the area deriving unit 32, the first calculation unit 34 calls the previously stored deformation area (the deformation area when the unit time is traced back) from the memory 27. . Then, the change rate of the deformation area is calculated by dividing the current deformation area by the previous deformation area.

  The deformation area change rate calculated first from the start of turning of the vehicle 12 is stored in the memory 27 as a reference value. The rate of change of the deformation area calculated after the second time is sent to the second calculation unit 36. Thereafter, the first calculation unit 34 calculates a change rate of the deformation area every time it receives data of the deformation area from the area deriving unit 32 (repeated every unit time), and sends it to the second calculation unit 36.

  The second calculator 36 receives the rate of change (change rate of deformation area) sent from the first calculator 34, and calculates the rate of change of the rate of change using the received rate of change and the reference value. Specifically, upon receiving the current change rate from the first calculation unit 34, the second calculation unit 36 calls the reference value (change rate calculated for the first time) stored in the memory 27, and the current change rate. The rate of change is calculated by dividing the rate by the reference value. The variation ratio calculated by the second calculation unit 36 is sent to the determination unit 38. Each time the second calculation unit 36 receives data on the change rate from the first calculation unit 34 (repeated every unit time), the second calculation unit 36 calculates a change rate of the change rate and sends it to the determination unit 38.

  Here, the rate of change and the rate of change in this embodiment will be described. FIG. 5 is a graph showing the relationship between the slip angle SA and the cornering force CF measured using a known indoor cornering tester. The plurality of graphs shown in FIG. 5 are all experimental results for one tire, and show the measurement results under a plurality of measurement conditions with various changes in the ground load (Load) and the camber angle (CA). Yes. FIG. 6 shows a graph of condition A extracted from the graphs of a plurality of conditions shown in FIG.

  As is clear from the graph shown in FIG. 5, even when the running conditions such as the load condition and the camber angle are changed, the aspect of the change in the cornering force CF with the increase in SA is the same. That is, in a region where the slip angle is relatively small (fine steering region), the cornering force CF increases as the slip angle SA increases, and the cornering force CF and the slip angle SA are in a substantially proportional relationship. When the slip angle is increased to some extent (middle rudder area), the substantially proportional relationship between the cornering force CF and the slip angle SA is lost, and when the slip angle is further increased (large rudder area), the size of the cornering force CF is saturated. (More specifically, it gradually decreases with increasing SA).

  The turning of the vehicle is performed by gradually increasing the steering angle of the wheel by the driver operating a steering device such as a steering wheel. In such turning, the slip angle of the wheel increases with time. The vehicle slip angle gradually increases from the fine rudder region to the middle rudder region and from the middle rudder region to the large rudder region as time elapses, for example, when the vehicle is steered greatly over a certain period of time. In such turning of the vehicle, it can be considered that the graph with the horizontal axis shown in FIG. 5 as the time axis corresponds to the graph showing the time-series change in the magnitude of the cornering force applied to the wheels during turning. it can.

  FIG. 6 also shows the relationship between the above-described deformation area calculated based on measurement data (time-series acceleration data) by an accelerometer installed on the tire and the slip angle SA. The change of the cornering force CF with respect to the change of the slip angle SA agrees well with the change of the deformation area with respect to the change of the slip angle SA. Details of the method for calculating the deformation area shown in FIG. 6 will be described later. As described above, it can be said that the size of the deformation area is a parameter representing the size of the cornering force. In general vehicle turning traveling in which the slip angle SA increases in time series, a graph with the horizontal axis shown in FIG. 5 as the time axis and the vertical axis shown in FIG. It can be considered that it corresponds to a graph showing the time series change of the area.

  That is, while the vehicle is turning, at the beginning of turning (the fine steering area), the deformation area increases with time, and the deformation area and time are in a substantially proportional relationship. When a certain amount of time has passed (medium rudder zone), the substantially proportional relationship between the deformation area and the elapsed time is broken. When the time further elapses (large rudder area), the size of the deformation area is saturated (more specifically, the deformation area gradually decreases with time). Such a relationship between the deformation area and time is such that the time and the slip angle of the wheel are in a proportional relationship, for example, the steering speed is constant and the traveling speed is increased at a constant rate (increase amount per unit time). This is true when the vehicle speed is increased (when the vehicle speed is constant) or when the steering angle is increased at a constant rate of increase (with the amount of increase per unit time constant) with the traveling speed constant.

  In the fine steering area where the deformation area and the time are approximately proportional, the rate of change of the deformation area (the amount of deformation per unit time) is relatively large, and the slope is substantially constant over time. In the middle rudder area, the rate of change of the deformation area gradually decreases with time. In the large rudder region, the rate of change is substantially constant even if time elapses. Such a change in the change rate can be easily determined from the graphs shown in FIGS. FIG. 7 is a graph showing an outline of a time-series change in the rate of change during turning of the vehicle. Even if the tires and turning conditions are different, as shown in FIG. 7, the rate of change is a constant value, a decreasing value, and a constant value (more specifically, a negative value that is almost zero) as time passes. Change. The change rate calculation unit 34 calculates such a change rate for each predetermined time interval while the vehicle 12 is turning. Then, the memory 27 stores the rate of change calculated first from the start of turning as a reference value.

  FIG. 8 is a graph showing the relationship between the slip angle and the rate of change calculated for each of the plurality of graphs shown in FIG. FIG. 8 is a graph obtained by calculating the change rate of the cornering force CF by changing the slip angle by 0.5 ° for each graph shown in FIG. As described above, during turning, the slip angle increases as the turning time elapses. During turning of a general vehicle, the horizontal axis in FIG. 8 is equivalent to the turning time. Can be thought of as As shown in FIG. 8, the value of the variation rate is a substantially constant value (both are about 0.90) in the fine steering area under any of the different turning traveling conditions. And in the area approaching from the fine steering area to the middle steering area, it gradually decreases. As shown in FIG. 9, the mode of change of the change rate is the same in each case even when the driving conditions are different, and each case is different even if the tire types are different. The same is true.

  Each time the change rate is calculated, the second calculation unit 36 calculates a variation rate of the calculated change rate with respect to the reference value. FIG. 9 is a graph showing an outline of a time-series change in the fluctuation ratio during the turning of the vehicle. The rate of change calculated every time the rate of change is calculated, that is, every unit time, is a graph obtained by standardizing the rate of change graph shown in FIG. 7 with a reference value. As can be judged from the change rate change modes shown in FIGS. 7 and 8, even if the tires and the turning conditions are different, the change rate is only 1.0 in the fine steering region as shown in FIG. It becomes a close constant value, and the rate of change decreases as it changes from the middle rudder area to the large rudder area. The second calculation unit 36 calculates such a fluctuation ratio in time series and sequentially transmits it to the determination unit 38.

  The determination unit 38 determines whether or not the value of the fluctuation ratio sent from the second calculation unit 36 is below a preset threshold value. When the value of the fluctuation ratio falls below a predetermined threshold value, the determination unit 38 has a reduced turning stability (that is, the turning stability of the vehicle is reduced and the vehicle is likely to slip). ). Then, a warning image for notifying the driver of the determination result (turning stability is lowered) is displayed on the display 40. The display 40 is not limited to such a warning image, and can sequentially display various data and calculation results handled by the processing device 20 such as a waveform of acquired acceleration data and various calculated parameters. Yes.

  The contents of the determination process in the determination unit 38 will be described. During the turning of the vehicle, the side slip of the wheel becomes remarkable because the vehicle approaches the large rudder region from the middle rudder region. If the relationship between the slip angle of the wheel and the cornering force is in the middle rudder zone and the slip angle further increases, the above relationship enters the large rudder zone, and the vehicle is slipped in a short time. Conversely, if the relationship between the slip angle of the wheel and the cornering force is in the middle rudder zone, and the slip angle decreases, the above relationship will enter the fine rudder zone, and there will be less side slip of the wheel, making stable and safe turning. It becomes a state. If the driver can know that the relationship between the slip angle of the wheel and the cornering force has entered the large steering area from the middle steering area while the vehicle is turning, the vehicle will slip. Can be prevented. For example, it is possible to prevent the vehicle from slipping by manipulating the vehicle so that the slip angle does not increase any more and the slip angle decreases. For example, the slip angle can be reduced by reducing the traveling speed of the vehicle or reducing the steering angle of the wheels. In evaluating the turning stability of the wheel, it is important to know whether or not the relationship between the slip angle of the wheel and the cornering force has entered from the middle rudder region to the large rudder region.

  As shown in FIG. 9, in the fine steering area, the value of the fluctuation ratio is a constant value very close to 1.0. The value of the fluctuation ratio decreases as it approaches from the fine rudder area to the middle rudder area, and further decreases as it approaches from the middle rudder area to the large rudder area. In the turning stability determination unit 38, it is determined whether or not such a fluctuation rate is lower than a predetermined value, so that whether or not the wheel of the vehicle that is turning is approaching the large rudder region from the middle rudder region. Can be determined.

  FIG. 10 is a flowchart of the wheel turning stability evaluation method of the present invention, which is carried out in such an apparatus 10. Hereinafter, the method for evaluating the turning stability of the wheel of the present invention, which is performed in the apparatus 10, will be described in detail.

  First, the driver of the vehicle 12 operates the vehicle steering device such as a steering wheel to steer the wheel 14, whereby the vehicle 12 starts to turn (step S100). When the cornering is started, the cornering start detecting means 18 detects that the cornering of the vehicle 12 is started, and the acceleration data of the wheels 14 (acceleration in the tire radial direction, tire width direction, and tire circumferential direction). (Data) acquisition is started (step S102).

  In step S102, the data processing unit 20 continuously receives acceleration information transmitted from the sensor units 16a to 16d and processes the acceleration information. More specifically, the data acquisition unit 22 acquires acceleration data in the tire radial direction, tire width direction, and tire circumferential direction amplified by the amplifier 4 as input data. The data supplied from the amplifier 4 is analog data, and the data acquisition unit 22 samples acceleration data in the tire radial direction, tire width direction, and tire circumferential direction at a predetermined sampling frequency, and converts them into digital data. Convert. At this time, as described above, the data acquisition unit 22 is based on the above-mentioned ID transmitted from each transmitter 15, and the acceleration measurement data transmitted from each wheel is the measurement data of the acceleration of the tire of which wheel. It is determined whether there is any wheel (wheel 14a to wheel 14d).

  Next, the deformation area of the surface of the tire 15 in the contact area is calculated from acceleration data in the tire radial direction, tire width direction, and tire circumferential direction (step S104). Hereinafter, the deformation area calculation processing in step S104 will be described in detail. FIG. 11 is a flowchart showing details of the processing in step S104 in the flowchart shown in FIG.

  12 and 13 show an example of results obtained by each process in the apparatus 10. The results shown in FIG. 12 and FIG. 13 are both processing results for acceleration data in the radial direction of the tire measured by the acceleration sensor 2. First, the acquired digital acceleration data is supplied to the signal processing unit 24, and smoothing processing using a filter is performed (step S122).

  FIG. 12A is an example of digital acceleration data in the tire radial direction acquired by the data acquisition unit 22. As shown in FIG. 12A, the measurement data supplied to the signal processing unit 24 contains a lot of noise components, so that the smoothing processing results in smooth data as shown in FIG. For example, a digital filter having a predetermined frequency as a cutoff frequency is used as the filter. The cut-off frequency varies depending on the rolling speed and noise components. For example, when the rolling speed is 60 (km / hour), the cut-off frequency is set to 0.5 to 2 (kHz). In addition, a smoothing process may be performed using a moving average process, a trend model, or the like instead of the digital filter.

  Next, the signal processing unit 24 removes the low-frequency background component 1 from the smoothed acceleration measurement data (step S124). For example, the background component 1 of acceleration in the tire radial direction includes the effects of an acceleration component and a gravity acceleration component of centrifugal force (centripetal force) during rolling of the tire. In FIG.12 (b), the waveform of the background component 1 is shown about the acceleration data of a tire radial direction. The background component is extracted by further smoothing the waveform data after the smoothing process obtained in step 104. For example, a digital filter having a predetermined frequency as a cutoff frequency is used. For example, when the rolling speed is 60 (km / h), the cutoff frequency is set to 0.5 to 2 (kHz). In addition, a smoothing process may be performed using a moving average process, a trend model, or the like instead of the digital filter. Further, in the waveform data after the smoothing process, for example, a plurality of nodes are provided at predetermined time intervals, and a first approximate curve is obtained by a least square method using a predetermined function group, for example, a cubic spline function. You may obtain | require by calculating. The node means a constraint condition on the horizontal axis that defines the local curvature (flexibility) of the spline function.

  The signal processing unit 24 subtracts the background component 1 thus extracted from the acceleration measurement data smoothed in step S122, so that the acceleration component based on the rotation of the tire and the gravitational acceleration component are obtained from the measurement data. Removed. FIG. 12C shows time-series data of acceleration in the tire radial direction after the background component is removed. As a result, an acceleration component (deformation acceleration time-series data) based on the ground deformation of the tread portion of the tire can be extracted. The smoothing process (step S122) and the background component removal (step S124) are performed for the digital acceleration data in the tire radial direction, the tire width direction, and the tire circumferential direction, respectively.

  At this time, the signal processing unit 24 determines that the rotation angle θ described above is 180 °, 540 °, 900 °,... From the time series data of acceleration based on tire deformation acquired in this way. Are extracted in advance. In the signal processing unit 24, in the graph of the time series data of the acceleration based on the tire deformation, the timing at which the acceleration based on the tire deformation takes the minimum value, the rotation angle θ is θ = 180 °, 540 °, 900 °. Extracted as the timing of. That is, the timing of these minimum values is extracted as the timing at which the acceleration sensor 2 fixed on the inner peripheral surface of the tire cavity region arrives (closest) to the center position of the tire contact surface as shown in FIG. This is because the position in the road surface vertical direction of the outer peripheral surface of the tire is defined by the road surface in the tire contact area.

  In the contact area, the road surface deforms the outer peripheral surface of the tire, which originally has a curvature, into a flat shape, so that the tire deforms in the thickness direction. As a result, the position of the inner peripheral surface of the tire cavity region fluctuates in the tire thickness direction (direction perpendicular to the road surface) in the ground contact region. The deformation in the thickness direction of the tire is minimized at the center position of the contact surface. The timing at which the acceleration based on the deformation of the tire, which is obtained by the acceleration sensor arranged on the inner peripheral surface of the tire cavity region, becomes the minimum, the rotation angle θ described above is 180 °, 540 °, 900 °, and so on. It can be said that From such timing when the rotation angle θ is 180 °, 540 °, 900 °,..., The time-series rotation angle θ in the rolling tire can be obtained.

  Next, in the ground contact timing deriving unit 26, the outer surface position 13 of the tire 15 rolling on the traveling road surface is set on the traveling road surface based on the time-series data of the acceleration in the tire radial direction based on the deformation of the tire. The timing of grounding and the timing at which the outer surface position 13 is separated from the grounding road surface are derived (step S126). FIG. 13 is an enlarged view of a part of the deformation acceleration time series data in the tire radial direction shown in FIG. The contact timing and the separation timing from the road surface can be extracted by obtaining two points where the acceleration changes suddenly and crosses 0 in the deformation acceleration time-series data extracted in step S124. The portion where the time series data of acceleration changes greatly in this way can be defined as the ground contact front end and the ground back end when the tread portion rotates and comes into the ground region, or when it comes out of the ground region. This is because the tire deforms rapidly.

  Next, in the trajectory deriving unit 28, time series data of acceleration in the tire width direction based on tire deformation and time series data of acceleration in the tire circumferential direction are time-integrated, and the time series deformation displacement of the outer surface position 13 is obtained. Calculated. Thereby, the locus | trajectory in XYZ space of the outer surface position 13 of the tire 15 rolling on a driving | running | working road surface is derived | led-out in detail (step S128).

  FIGS. 14A to 14C are graphs each schematically showing a processing result performed by the locus deriving unit 28 in step S128. The graphs shown in FIGS. 14A to 14C are the processing results for the deformation acceleration time series data in the tire radial direction. The trajectory deriving unit 28 first performs time integration of the second floor on the deformation acceleration time-series data to generate displacement data. FIG. 14A shows a result of second-order integration with respect to time of time series data (deformed acceleration time series data) of acceleration from which the first background component has been removed in the data processing unit. As shown in FIG. 14A, it can be seen that the displacement increases with time. This is because the time series data of acceleration to be integrated includes a noise component and is integrated by integration. In general, when the amount of deformation or displacement of a point of interest in a tread portion of a tire that rolls in a steady state is observed, a periodic change is shown with the rotation period of the tire as a unit. Therefore, it is usually not possible for the displacement to increase with time. Therefore, the following processing is performed on the displacement data so that the displacement data obtained by performing the second-order time integration shows a periodic change in units of the tire rotation cycle.

  That is, the noise component included in the displacement data is calculated as the background component 2 in the same manner as the method for calculating the background component 1. At this time, the amount of deformation during rolling of the tire in the region including the contact region with the road surface can be accurately obtained by using the above-described time-series rotation angle θ. More specifically, the area on the circumference of the tire is divided into a first area including a contact area with the road surface and a second area other than this, and the first area is larger than θ = 90 degrees 270. An area of less than 85 degrees, greater than 450 degrees and less than 720 degrees, greater than 810 degrees and less than 990 degrees is defined as the second area, θ = 0 degrees to 90 degrees and 270 degrees to 360 degrees, 360 degrees to 450 degrees The following regions are defined: 630 ° to 720 °, 720 ° to 810 °, and 980 ° to 1070 °. The background component 2 uses the plurality of circumferential positions (time corresponding to θ or θ) in the second region as nodes, and uses a predetermined function group, and the first region and the second region It calculates | requires by calculating a 2nd approximation curve with the least squares method with respect to the data of an area | region. The node means a constraint condition on the horizontal axis that defines the local curvature (flexibility) of the spline function. In FIG. 14B, a second approximate curve representing the background component 2 is indicated by a dotted line. In the example of FIG. 14B, the position indicated by “Δ” in FIG. 14B, that is, θ = 10, 30, 50, 70, 90, 270, 290, 310, 330, 350, 370, 390. , 410, 430, 450, 630, 650, 670, 690, 710, 730, 750, 770, 790, 810, 990, 1010, 1030, 1050, 1070 degrees.

  A second approximate curve indicated by a dotted line in FIG. 14B is calculated by performing function approximation on the displacement data shown in FIG. 14A with a cubic spline function passing through the data points of the nodes. Is done. When performing function approximation, there are no nodes in the first region, function approximation is performed using only a plurality of nodes in the second region, and the weighting factor of the second region used in the least square method performed in function approximation is used. The processing is performed with 1 being set to 1, and the weighting coefficient of the first region being set to 0.01. Thus, when calculating the background component 2, the first weighting factor is reduced and the node is not defined in the first region. The background component 2 is calculated mainly using the displacement data in the second region. It is to do. In the second region, deformation due to contact of the tread portion is small and the deformation changes smoothly on the circumference, so that the amount of deformation of the tire is small on the circumference and the change is also extremely small. On the other hand, in the first region, the tread portion of the tire is greatly displaced and rapidly changes based on the ground deformation. For this reason, the amount of deformation based on ground deformation is large and rapidly changes on the circumference. That is, the deformation amount of the tread portion in the second region is substantially constant as compared with the first deformation amount. Thus, by calculating the first approximate curve mainly using the displacement data obtained by the second order integration of the second area, the first area including not only the second area but also the ground contact area with the road surface is obtained. The amount of deformation during rolling of the tire in the region can be obtained with high accuracy. In FIG. 14B, the second approximate curve calculated mainly using the displacement data of the second region is indicated by a dotted line. In the second region, the second approximate curve substantially matches the displacement data (solid line).

  Then, the approximate curve calculated as the background component 2 is subtracted from the displacement data, and the distribution of the deformation amount based on the ground deformation of the tread portion is calculated. FIG. 14C shows the distribution of deformation based on the ground deformation of the tread portion, which is calculated by subtracting the second approximate curve (dotted line) from the displacement signal (solid line) shown in FIG. 14B. Show. FIG. 14C shows a distribution of deformation amounts for three rotations (three times of ground contact) when a predetermined measurement position on the tread portion rotates around the circumference and is displaced. It can be seen that the amount of deformation changes with each contact. The deformation amount calculated by such a method coincides with the deformation amount when the simulation is performed using the tire finite element model with high accuracy. In this manner, the relationship between the tire rotation angle θ (and time) and the deformation displacement in the tire radial direction as shown in FIG. 14C is obtained. By performing the same process for the tire width direction and the tire circumferential direction, the relationship between the tire rotation angle θ (and time) and the deformation displacement in the tire width direction, the tire rotation angle θ (and time) and the tire circumference A relationship of deformation displacement in the direction is obtained respectively.

  In the locus deriving unit 28, the tire radial direction displacement, the tire width direction displacement, and the tire circumferential direction displacement of the tire outer surface position 13 with respect to the tire rotation angle are obtained in this way. FIGS. 15A and 15B show a predetermined portion of the tire (acceleration sensor ground contact position) calculated using acceleration data based on tire deformation obtained using a known indoor cornering tester. It is a figure which shows the locus | trajectory in the said XYZ space. FIGS. 15A and 15B are graphs in which the position of the predetermined portion of the tire is changed to an orthogonal coordinate system based on the displacement of the predetermined portion of the tire with respect to the rotation angle of the tire. FIG. 15A shows a locus of the acceleration sensor 2 in a coordinate system composed of the X direction and the Y direction. FIG. 15B shows a locus of the acceleration sensor 2 in a coordinate system composed of the Y direction and the Z direction. In step 124, the rotation locus calculator 28 derives such a rotation locus of the outer surface position 13 of the tire 15 and sends the derived rotation locus to the deformation area derivation unit 32.

  Next, the deformation area deriving unit 32 calculates a deformation area representing the magnitude of deformation of the tire 15 in the contact area from the contact and separation timing of the outer surface position 13 and the trajectory of the outer surface position 13 (step S129). . Specifically, the time-series deformation displacement in the tire width direction derived by the trajectory deriving unit 28 is integrated from the time of contact of the outer surface position 13 to the time of separation of the outer surface position 13 derived by the contact timing deriving unit 26. And ask. In this way, the deformation area calculation unit 32 calculates the deformation area of the tire 15 as indicated by the oblique lines in FIG. The deformation area thus obtained corresponds to the area of the colored region on the graph shown in FIG.

  As described above, the relationship between the deformation area and the time is established with high accuracy in the turning traveling in which the time and the slip angle of the wheel are in a proportional relationship. For example, when the steering speed is constant and the travel speed is increased at a constant rate (with a constant increase per unit time), or the travel angle is constant and the steering angle is increased at a constant rate (increase per unit time) This is true with increasing accuracy (assuming a constant amount). For example, a general passenger vehicle or a truck vehicle sequentially increases the speed (for example, 50 km / h → 60 km / h → 80 km) at a corner having a constant turning radius (for example, 100R) such as an entrance to a highway or a junction. (Increased to / h), the vehicle can operate with high accuracy. Alternatively, a common corner of a general road where the turning radius gradually decreases (for example, the turning radius gradually decreases from 80R → 50R → 30R), a general passenger vehicle or a truck vehicle has a legal speed (60 km / h) It is established with high accuracy when traveling at a constant traveling speed (for example, 50 km / h) as follows.

  The deformation area calculated by such a method matches the deformation area when the simulation is performed using the tire finite element model with high accuracy. In the present embodiment, the deformation area is derived in this way. For example, when a general passenger vehicle or truck vehicle travels on a general road or an expressway, such a deformation area may be derived every unit time (for example, 0.5 seconds). When driving on a general vehicle or highway with a general passenger vehicle or truck vehicle, the vehicle wheels are sufficiently within the range of the fine steering after 0.5 seconds from the start of turning, and at least the tires start turning It can be said that it is rotating more than 1 rotation from the time. If the unit time is set to 0.5 seconds, for example, the wheels of the vehicle are still in the range of the fine steering area in each case described above. The tire has rotated at least once, and the deformation area can be calculated. The calculated deformation area is stored in the memory 27. The unit time is not limited to 0.5 seconds. For example, when the passenger vehicle travels at a high speed corner such as a circuit at a high speed (for example, 100 km or more), the unit time is shorter. Should be set. In the present invention, the unit time may be appropriately set to a suitable value according to measurement conditions (vehicle driving conditions, tire conditions, measuring device conditions, etc.).

  When the calculation of the deformation area in step S104 is the first calculation after the vehicle 12 starts turning (when the determination result in step S106 is Yes), the process returns to step S104 to calculate the next deformation area. To do. When the calculation of the deformation area in step S104 is the calculation after the second time after the vehicle 12 starts turning (when the determination result in step S106 is No), the derived deformation area is stored in the memory 27. And sent to the first calculation unit 34.

  Then, the first calculation unit 34 calculates the change rate of the deformation area using the received deformation area and the deformation area previously calculated and stored in the memory 27 (step S108). Specifically, the first calculation unit 34 receives the deformation area calculated and sent for each unit time from the area deriving unit 32, and the deformation at the point in time that is stored in the unit 27 from the memory 27 earlier. Call the area and divide the current deformation area by the previous deformation area to calculate the deformation area change rate (change amount of deformation area per unit time).

  When the calculation of the deformation area change rate in step S108 is the first calculation after the vehicle 12 starts turning (when the determination result in step S110 is Yes), the calculated deformation area change rate is The reference value is stored in the memory 27 (step S112). And it returns to step S104 and repeats the process after step S104. When the calculation of the change rate of the deformation area in step S108 is the calculation after the second time after the vehicle 12 starts turning (when the determination result in step S110 is No), the change rate of the derived deformation area is calculated. Is sent to the fluctuation ratio calculation unit 36.

  Then, the second calculation unit 36 receives the change rate (change rate of the deformation area) sent from the first calculation unit 34, and calculates the change rate of the change rate using the received change rate and the reference value. (Step S114). Specifically, every time the second calculation unit 36 receives a change rate sent from the first calculation unit 34 per unit time, the second calculation unit 36 calls the reference value stored in advance from the memory 27 and sets the current change rate as a reference. Divide by value to calculate the rate of change.

  In the present invention, the reference value is not limited to the rate of change calculated first after the vehicle starts turning. For example, the rate of change calculated the second time after the vehicle starts turning may be the rate of change calculated the third time. However, the reference value is preferably a value of the rate of change in the fine steering area, and is preferably a value of the rate of change calculated within, for example, 0.5 seconds from the start of turning. It is more preferable that the rate of change calculated first after the vehicle starts turning. Note that the reference value may be, for example, an average value of a plurality of change rates calculated within a predetermined time or a predetermined number of times after the vehicle starts turning. Also in this case, it is preferable that the reference value is calculated based on the rate of change in the fine steering region, the predetermined time is, for example, 1.0 seconds, and the predetermined number of times is, for example, 3 times. Is preferred. When a general passenger vehicle or a truck vehicle travels on a general road or a highway (for example, a vehicle equipped with tires having a tire circumference of about 2.0 m (195 / 65R15) travels on a highway at a speed of 80 km. For example, when the vehicle travels at / h), the wheel of the vehicle is sufficiently within the range of the fine steering region at the time when 1.0 second has elapsed from the start of the turn, and the tire has rotated at least 3 to 5 times or more from the start of the turn. If the predetermined time is set to, for example, 1.0 second, a plurality of deformation areas can be calculated in a state where the vehicle wheels are still in the fine steering area, and fluctuations according to the deformation area in the fine steering area. Multiple ratios can be derived. The variation ratio calculated by the second calculation unit 36 is stored in the memory 27 and sent to the determination unit 38. The predetermined time is not limited to 1.0 seconds. Further, the predetermined number of times is not limited to three. In the present invention, the predetermined time and the predetermined number of times may be appropriately set to appropriate values according to measurement conditions (vehicle driving conditions, measuring device conditions, etc.).

  Whenever the value of the fluctuation ratio is sent from the second calculation section 36, the determination section 38 determines whether or not the sent fluctuation ratio is below a preset threshold value (step S116). The threshold value may be set to 0.60, for example. That is, when the above-described variation ratio (see FIG. 9) is less than 0.60, it may be determined that the possibility that the vehicle 12 slips and the vehicle 12 is in a slip state is high. As described above, this means that the fluctuation ratio is about 1.0 in the fine steering area, and that this fluctuation ratio is less than 0.60 indicates that the state of the wheel is approaching the large steering area. It is because it can be judged that it is. When it is determined that the vehicle 12 is likely to be in a slip state at a stage where the vehicle 12 is less likely to actually be in a slip state and the wheel state is approaching the middle rudder range, the threshold is For example, it may be set to 0.88.

  If the determination result in step S116 is No, the process returns to step S104, and the processes after step S104 are repeated. If the determination result in step S116 is Yes, the determination unit 38 displays a warning image on the display 40 for informing the driver that the turning stability of the vehicle is low and the vehicle is likely to slip. It is displayed (step S118). Each process of step S104-step S116 is repeatedly implemented until turning driving | running | working is complete | finished (until the determination result of step S120 becomes Yes). For example, the measurement may be repeated until the measurement result of the steering angle of each wheel by the turning start detection unit 18 becomes 0 and the vehicle 12 is in a straight traveling state.

  According to the wheel turning stability evaluation method and the wheel turning stability evaluation device of the present invention, when the vehicle is actually turned under various driving conditions, the slip state is determined under any driving condition. You can know what will be. In this way, it is possible to evaluate the turning stability of the wheel in a state where it is actually mounted on the vehicle (a margin until a slip state is reached). In addition, by displaying the determination result on the display 40, for example, the vehicle driver is informed of the turning stability of the wheel (margin to the slip state) in real time while the vehicle is turning. You can also

  In addition, you may use the determination result by the turning stability evaluation apparatus of the wheel of this invention for vehicle control. For example, if the rate of change falls below a threshold while the vehicle is turning, the vehicle is in a skid state by controlling the vehicle so that the slip angle does not increase any more and the slip angle decreases. You may comprise the control apparatus of a vehicle which prevents this. In such a vehicle control device, for example, the slip angle may be reduced by reducing the traveling speed of the vehicle or reducing the steering angle of the wheels.

  Further, by using the turning stability evaluation device for a wheel of the present invention, it is possible to quantitatively and qualitatively evaluate the turning performance unique to the tire. For example, the turning performance unique to the tire may be quantitatively evaluated by checking the speed at which the fluctuation ratio is equal to or less than the threshold by repeatedly driving the vehicle while changing only the traveling speed. At this time, all the traveling conditions other than the traveling speed (the condition of the vehicle on which the tire is mounted, the condition of the steering angle, etc.) may be all the same. In addition, for example, a tire with various changes in tires mounted on the same vehicle, and the vehicle repeatedly turning under the same running conditions, and having a fluctuation ratio equal to or less than a threshold, is a tire with insufficient turning performance. You may judge.

  In the present invention, by providing a plurality of acceleration sensors on the inner peripheral surface of the tread portion on the circumference (along the tire circumferential direction), the ground contact state at the circumferential position of the tread portion can be simultaneously acquired. Furthermore, by providing a plurality of acceleration sensors in the width direction of the tire and obtaining the contact length in the width direction and the distribution of the contact area, the contact shape of the rolling tire can be acquired. In addition, as described above, by providing a plurality of acceleration sensors on the inner circumferential surface of the tread portion on the circumference, it is also possible to acquire the distribution of force in the tire circumferential direction that occurs in the ground contact area of the wheel. Further, by providing a plurality of acceleration sensors in the tire width direction, the distribution in the tire width direction of the cornering force generated in the wheel contact area can be obtained.

  The wheel turning stability evaluation method and the wheel turning stability evaluation device of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. Of course, improvements and changes may be made.

It is a schematic block diagram of the turning stability evaluation apparatus of a wheel explaining an example of the turning stability evaluation apparatus of the wheel of this invention. It is a schematic block diagram of the turning stability evaluation apparatus of a wheel explaining the sensor unit and the data processing unit in the turning stability evaluation apparatus of a wheel shown in FIG. (A) is the perspective view which looked at the tire of the wheel provided with the sensor unit shown in FIG. 2 from the grounding road surface side, and (b) is a cross section showing an enlarged part of the cross section of the tire. FIG. (A) is a side view of the tire shown in FIG. FIG. 4B is a bottom view of the tire shown in FIG. 3 as viewed from the ground road surface side. It is a graph which shows about the relationship between the slip angle SA and the cornering force CF which were measured using the well-known indoor cornering tester. It is a graph of condition A among the graphs of a plurality of conditions shown in FIG. It is a graph which shows the outline of the time-sequential change of a change rate during the turning driving | running | working of a vehicle. 6 is a graph showing a relationship between a slip angle and a change rate calculated for each of a plurality of graphs shown in FIG. 5. It is a graph which shows the outline of the time-sequential change of the fluctuation | variation rate during the turning driving | running | working of a vehicle. It is a flowchart figure of an example of the turning stability evaluation method of the wheel of this invention. It is a flowchart figure which shows the detail of a deformation | transformation area calculation process among an example of the turning stability evaluation method of the wheel of this invention. (A) is the digital acceleration data of the tire radial direction acquired by the tire acceleration data acquisition part. (B) And (c) is a graph which shows the processing result in the data processing part of the digital acceleration data shown to (a). It is a figure which expands and shows a part of deformation | transformation acceleration time series data of a tire radial direction shown in FIG.12 (c). (A)-(c) is a graph which shows typically the processing result in a rotation locus calculating part, respectively. (A) And (b) is a figure which shows the locus | trajectory of the acceleration sensor installed in the tire calculated based on the deformation acceleration data of the tire acquired using the well-known indoor cornering tester.

Explanation of symbols

DESCRIPTION OF SYMBOLS 2 Acceleration sensor 3 Receiver 4 Amplifier 10 Wheel turning stability evaluation apparatus 11 Inner surface position 12 Vehicle 13 Outer surface position 14a-14d Wheel 15a-15d Tire 16a-16d Sensor unit 17 Transmitter 20 Data processing unit 21 Processing means 22 Data acquisition Part 23 CPU
24 signal processing unit 26 timing deriving unit 27 memory 28 trajectory deriving unit 30 determining means 32 area deriving unit 34 first calculating unit (change rate calculating unit)
36 Second calculation unit (variation rate calculation unit)
38 judgment part 40 display

Claims (10)

A method of evaluating the turning stability of a wheel when a vehicle including a wheel on which a tire is mounted is turning on a road surface,
When the vehicle is turning, the amount of lateral displacement of the tire at a predetermined portion of the tire caused by lateral deformation of the tire on the outer peripheral surface of the tire is grounded from the front end of the tire. A step of continuously deriving the integrated value up to the rear end every unit time;
Each time the integrated value of the displacement amount is derived, the integrated value of the displacement amount derived from the derived integrated value of the displacement amount and the integrated value of the displacement amount derived one time ago per unit time. A first calculation step of repeatedly calculating the amount of change as a rate of change in tire deformation;
Whenever the rate of change of the tire deformation is calculated, the rate of change of the calculated rate of change of the tire deformation with respect to the reference value is calculated using the previously calculated rate of change of the tire deformation as a reference value. A calculation step;
Determining the turning stability of the wheel representing a margin until the wheel reaches a side-slip state based on the fluctuation ratio calculated in the second calculating step. Turning stability evaluation method.   In the deriving step, acceleration data in the tire width direction of the predetermined portion of the tire, which is measured by an acceleration sensor installed at a position corresponding to the predetermined portion of the tire, along with the lateral deformation of the tire is used. The wheel turning stability evaluation method according to claim 1, wherein an integrated value of the displacement amount is derived.   The wheel acceleration stability evaluation method according to claim 2, wherein the acceleration sensor is installed on a tire inner circumferential surface facing a tire cavity region of a tread portion of the tire. Acceleration data in the tire radial direction of a predetermined portion of the tire, and the vehicle during turning while the vehicle is turning while the tire is rolling and the outer peripheral surface of the tire is brought into contact with the ground. A data acquisition step of acquiring acceleration data in a tire width direction of a predetermined portion of the tire, along with a lateral deformation of the tire on an outer peripheral surface of the tire,
In the derivation step,
Based on the acceleration data in the tire radial direction, the timing at which the predetermined portion contacts the road surface and the timing at which the predetermined portion separates from the road surface are obtained,
In addition, the time-series data of the amount of lateral displacement of the tire at a predetermined portion of the tire due to the lateral deformation of the tire is obtained by performing second-order time integration on the acceleration data in the tire width direction. ,
The integrated value of the displacement amount is derived by integrating the time series data of the displacement amount from the timing at which the predetermined portion contacts the road surface to the timing at which the predetermined portion separates from the road surface. The method for evaluating the turning stability of a wheel according to any one of claims 2 and 3 . In the deriving step, two timings at which acceleration data in the tire radial direction of the predetermined portion of the tire crosses 0 in accordance with the deformation of the outer peripheral surface of the tire are obtained. The wheel turning stability evaluation method according to claim 4, wherein the timing of the separation is set. 6. The variation ratio is calculated in the second calculation step using the change rate of the tire deformation first calculated after the vehicle starts turning as the reference value. The wheel turning stability evaluation method according to any one of the above. In the determination step, the fluctuation ratio calculated in the second calculation step is compared with a predetermined threshold value, and when the value of the fluctuation ratio falls below the threshold value, the wheel reaches a side slip state. The method for evaluating the turning stability of a wheel according to any one of claims 1 to 6, wherein it is determined that the risk is high. An apparatus for evaluating the turning stability of a wheel when a vehicle including a wheel on which a tire is mounted is turning on a road surface,
  A memory capable of storing numerical information;
  When the vehicle is turning, the amount of lateral displacement of the tire at a predetermined portion of the tire caused by lateral deformation of the tire on the outer peripheral surface of the tire is grounded from the front end of the tire. A deriving unit for continuously deriving the integrated value up to the rear end for each unit time and storing it in the memory;
  Each time the integrated value of the displacement amount is derived, the integrated value of the derived displacement amount is received, and the integrated value of the displacement amount previously derived stored in the memory is called and derived. The amount of change per unit time of the integrated value of displacement is repeatedly calculated as the rate of change of tire deformation from the integrated value of displacement and the integrated value of displacement stored previously. 1 calculation unit;
  Each time the rate of change of the tire deformation is calculated, the calculated rate of change of the tire deformation is received, and the rate of change of the tire deformation calculated using the previously calculated rate of change of the tire deformation as a reference value. A second calculation unit that repeatedly calculates a variation ratio with respect to the reference value;
  Receiving the fluctuation rate of the tire deformation change rate calculated by the second calculation unit, and based on the change rate, the turning stability of the wheel representing a margin until the wheel reaches a side slip state. A wheel turning stability evaluation apparatus comprising: a determination unit for determining. Detecting means for detecting that the vehicle has started turning while the vehicle is running;
  The first calculation unit stores, in the memory, the change rate of the tire deformation calculated first after the detection unit detects the start of turning of the vehicle as the reference value.
  9. The wheel turning stability evaluation according to claim 8, wherein the second calculation unit reads the reference value from the memory and calculates the variation ratio every time the change rate of the tire deformation is calculated. apparatus. The determination unit compares the variation ratio calculated by the second calculation unit with a predetermined threshold value, and when the value of the variation ratio falls below the threshold value, the wheel reaches a side slip state. The wheel turning stability evaluation device according to claim 8 or 9, wherein it is determined that the risk is high.

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