Burst risk assessment method and apparatus, burst risk reduction method and apparatus

Abstract

The present invention provides a method and apparatus for appropriately assessing the risk of a tire bursting, and a method and apparatus for reducing that risk when it is high. [Solution] When the risk of a tire 3 mounted on a wheel 2i of a vehicle 1 bursting is evaluated by the processor 5, the tire surface temperature is calculated, and based on the calculated tire surface temperature, a surface temperature coefficient representing the risk of decreased rigidity of the tire structure due to the rise in the surface temperature of the tire 3 is calculated, and based on the shear force acting on the surface of the tire 3 and the surface temperature coefficient, a burst risk level is calculated as an evaluation index for the risk of the tire bursting, and the higher the burst risk level, the greater the risk of the tire bursting. Furthermore, if the calculated burst risk level is above a predetermined value, the risk of the tire 3 bursting is reduced by controlling the physical quantities of the vehicle that contribute to the sensitivity of the rise in the surface temperature of the tire 3.

Description

[Technical Field]

[0001] This invention relates to a burst risk assessment method and apparatus, and a burst risk reduction method and apparatus. [Background technology]

[0002] Patent Document 1 below discloses a technology that involves attaching a temperature sensor and a pressure sensor to the wheel of a vehicle, monitoring the internal temperature and air pressure of the tire mounted on the wheel using these sensors, and predicting a tire burst if abnormalities are detected compared to normal values. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2005-212669 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, the tire burst (hereinafter simply referred to as "burst") prediction technology described in Patent Document 1 above requires temperature sensors and pressure sensors, and the detection period is generally around 30 seconds, which may cause delays in burst prediction. In other words, it is desirable to be able to appropriately evaluate the risk of a tire burst and to reduce the risk when it is high. The present invention aims to provide a burst risk assessment method and apparatus that can appropriately assess the risk of a tire bursting, and a burst risk reduction method and apparatus that can reduce the risk when it is high. [Means for solving the problem]

[0005] One aspect of the present invention involves evaluating the risk of a tire bursting when mounted on a vehicle's wheel using a computing device. This involves calculating the tire's surface temperature, calculating a surface temperature coefficient based on the calculated tire's surface temperature to represent the risk of reduced rigidity in the tire structure due to rising surface temperature, calculating a burst risk level as an evaluation index for the risk of a tire bursting based on the shear force acting on the tire's surface and the surface temperature coefficient, and evaluating that a higher burst risk level indicates a greater risk of the tire bursting. Another aspect of the present invention involves controlling a physical quantity of the vehicle that contributes to the sensitivity of the tire surface temperature rise when the burst risk level calculated by the burst risk evaluation above is above a predetermined value, thereby reducing the risk of the tire bursting. [Effects of the Invention]

[0006] According to one aspect of the present invention, the risk of a tire bursting can be appropriately evaluated, and if the risk is high, it can be reduced. [Brief explanation of the drawing]

[0007] [Figure 1] This is a system configuration diagram of a vehicle equipped with a tire burst risk assessment and reduction system, which is one embodiment of the present invention. [Figure 2] This is an explanatory diagram of the change in vertical load on each wheel of the vehicle shown in Figure 1. [Figure 3] This is an explanatory diagram of the heat generation and heat dissipation in a wheel tire. [Figure 4] Figure 1 is a flowchart of the calculation process performed in the tire surface temperature calculation unit. [Figure 5] This is an explanatory diagram of the tire temperature dependence model. [Figure 6] Figure 1 is a flowchart of the calculation process performed in the burst risk control unit. [Figure 7] This is the map used to calculate the surface temperature coefficient in the calculation process shown in Figure 6. [Figure 8]This is an explanatory diagram illustrating a modified example of the surface temperature coefficient map in Figure 7. [Figure 9] This is a map of wheel load control in burst risk reduction control. [Figure 10] This is a map of yaw moment control in burst risk reduction control. [Modes for carrying out the invention]

[0008] Embodiments of the present invention will be described below with reference to the drawings. Note that the drawings are schematic and may differ from actual ones. The vehicle 1 of the embodiment shown in Figure 1 is an autonomous vehicle having four wheels 2i, similar to a typical passenger vehicle: the front right wheel 2FR, the front left wheel 2FL, the rear right wheel 2RR, and the rear left wheel 2RL. The vehicle 1 is also equipped with a driving control device 36 for autonomous driving the vehicle 1. The vehicle 1 is also equipped with a drive electric motor as a drive source 13 for the drive device that drives the vehicle 1, and the operating state of this drive electric motor is controlled by a drive controller 13a. It is also possible to apply braking force to each wheel 2i by regenerating the drive electric motor, which is the drive source 13. Furthermore, this vehicle 1 is equipped with a hydraulic brake device as a braking device for braking the vehicle 1, and therefore each wheel 2i is provided with a hydraulic brake mechanism 12. While the hydraulic brake mechanism 12 can also apply braking force to each wheel 2i by operating the brake pedal, to enable autonomous driving, the vehicle 1 is equipped with a hydraulic control unit 12a that increases, maintains, and decreases the hydraulic pressure in the hydraulic brake mechanism 12 of each wheel 2i. This hydraulic control unit 12a is configured to include, similar to those used in well-known vehicle behavior control devices, a pressurizing pump for increasing or decreasing the hydraulic pressure to the hydraulic brake mechanism 12, a switching valve for switching between the hydraulic pressure from the brake pedal and the hydraulic pressure from the pressurizing pump, and hydraulic control valves that can individually increase, maintain, and decrease the hydraulic pressure in the hydraulic brake mechanism 12 of each wheel 2i. The components of this hydraulic control unit 12a operate in accordance with control signals from the hydraulic controller 12b. Therefore, by individually controlling the hydraulic pressure in the hydraulic brake mechanism 12 of each wheel 2i, it is also possible to control the yaw moment (motion) of the vehicle.

[0009] Vehicle 1 is also equipped with a steering device for steering the vehicle 1, and a controller for controlling it (neither shown). In this embodiment, an electric power steering device is provided as the steering device, and the driving control device 36 has a road surface friction coefficient calculation unit that calculates the road surface friction coefficient as the road surface friction coefficient from the magnitude of the road surface reaction torque in the electric power steering device. One of the various other methods that have been implemented can also be applied to calculate the road surface friction coefficient. Vehicle 1 is also equipped with an environment recognition system for recognizing the surrounding environment, and a communication system for vehicle-to-infrastructure communication and vehicle-to-vehicle communication, and a controller for controlling each of these systems (neither shown). The driving control device 36 for automatically driving this vehicle 1, for example, based on control inputs such as surrounding environment information obtained from the environment recognition system and communication information obtained from the communication system, it manages the control state of the controlled objects in the drive device, braking device and steering device, and outputs control commands to the drive controller, braking controller and steering controller based on the driving action plan used in current automated driving logic of Level 3 or higher. As shown in Figure 3, each wheel 2i is fitted with a tire (pneumatic tire) 3.

[0010] Furthermore, this vehicle 1 is equipped with a tire surface temperature control device 4 that supplies the surface temperature of the tires 3 of each wheel 2i to the aforementioned driving control device 36 and controls the surface temperature of the tires 3 of each wheel 2i. The tire surface temperature control device 4 is configured as a functional unit comprising a tire surface temperature calculation unit 6 that calculates the surface temperature of each wheel 2i and a burst risk control unit 7. The driving control device 36, for example, according to the tire temperature dependence model that represents the correlation between the surface temperature of the tire 3 and the maximum friction coefficient of the tire 3 shown in Figure 5, calculates the surface temperature T of the tires 3 of each wheel 2i by the tire surface temperature calculation unit 6. i The maximum friction coefficient μ of each wheel 2i TMAXi Obtain this maximum friction coefficient μ TMAXiUsing this, control commands to, for example, the drive controller, hydraulic controller, and steering controller are calculated and set. Before explaining the specific configuration and operation of these tire surface temperature calculation unit 6 and burst risk control unit 7, we will explain the recent trends in tire bursts and burst risk levels. For example, with the electrification of vehicles, the mass of vehicles has increased, and in response, the width of tires (tread width) has decreased in order to improve fuel efficiency (lower electricity consumption) and reduce noise. In addition, not only racing vehicles but also general vehicles tend to have increased downforce while driving, and the load on the tires increases accordingly. Furthermore, vehicle (motion) control using the longitudinal force, lateral force, or wheel load generated by the tires has become widespread, and although tires are used effectively as a result, the load on the tires also increases. As a result, cracks tend to occur in the sidewall of the tire, the tread separates, and the tire tends to burst. Even if run-flat tires become more common in the future, the risk of bursts due to tread separation is expected to remain. Considering the physical properties of tires, the decrease in rigidity of the tire structure that leads to a tire burst due to tread separation is related to the tire temperature and the force that tears the tread portion of the tire at the sidewall.

[0011] The force that tears the tire tread at the sidewall is a shear force acting on the tire surface (tread) and depends on the frictional force of the tire surface (tread). During vehicle cornering, the frictional force between the tire and the road surface acts on the tire surface (tread) as a shear force that tears the tire tread at the sidewall. On the other hand, in the case of radial tires, for example, the rubber that makes up the sidewall and tread is integrated before heating and pressurizing molding, but the adhesive rubber that holds the rubber together contains a lot of sulfur, and when the sulfur reaches a certain temperature, a chemical reaction (vulcanization) begins, and at that point its strength becomes lower than other rubber parts, reducing the rigidity of the tire structure. If we consider that the shear force that tears the tread acts on the inner part of the tread at the sidewall, the risk of tire bursting increases when the temperature of this part reaches the vulcanization start temperature. It is possible to calculate (estimate) the tire surface temperature (tread temperature), so for example, the ease or difficulty of heat transfer in a tire can be set as the surface temperature coefficient (= tire tearing tendency). The starting point for the rise in tire temperature as the vehicle moves is the outer surface of the tire, i.e., the tread, where frictional force acts with the road surface. For example, the greater the tread thickness, the more difficult it is for heat to be transferred to the inner part of the tread in the sidewall. Therefore, it is possible to set the product of this surface temperature coefficient and the tire's frictional force as the tire burst risk level, and the higher this burst risk level, the more likely the tire is to burst. Furthermore, as mentioned above, the inner part of the tread in the sidewall is thought to be subjected to load as the tire rubber continues to flex while the vehicle is turning, causing the temperature to rise, so it is desirable to reflect the duration of the vehicle's turning in the surface temperature coefficient.

[0012] Figure 7 shows a map of this surface temperature coefficient. According to this control map, a larger surface temperature coefficient is set as the tire surface temperature increases and as the turning duration increases. In this map, a larger surface temperature coefficient is set as the tire surface temperature increases, but even if the tire surface temperature is not particularly high, a larger surface temperature coefficient is set as the turning duration increases. This reflects the fact that while the vehicle is turning, the temperature of the inner part of the tire tread on the sidewall rises, increasing the risk of bursting. This example shows a case where the tire is a specific tire mounted on the wheels of a so-called new car, a so-called original equipment tire, and its physical properties are known and the surface temperature coefficient can be determined. In contrast, as mentioned above, when the ease or difficulty of heat transfer of the tire is reflected in the surface temperature coefficient, as shown in Figure 8, for example, the curve for a surface temperature coefficient of 1.0 transitions by sliding left and right on the map, i.e., in the direction of the turning duration axis. In other words, if the tire conducts heat easily, the temperature rise from the tire surface (tread) to the inside of the tread is rapid, so the burst risk level increases with a short turning duration, shifting to the left. Conversely, if the tire conducts heat poorly, the temperature rise to the inside of the tread is slow, so the burst risk level does not increase significantly with the same turning duration, shifting to the right. Considering only the tread surface, this reflects the property that, as mentioned above, the thicker the tread, the less heat it conducts.

[0013] Furthermore, in this embodiment, when the burst risk level is above a predetermined value (first threshold), the burst risk is reduced by controlling the physical quantities of the vehicle that contribute to the sensitivity of the tire surface temperature rise. Examples of the physical quantities of the vehicle that contribute to the sensitivity of the tire surface temperature rise include the wheel load of each wheel, the slip angle of each wheel, and the driving speed. To reduce the burst risk, the wheel load of the wheel with a high burst risk should be increased, the slip angle should be decreased, and the driving speed should be decreased. Increasing the wheel load can be achieved, for example, by adding or increasing the braking force of the vehicle for the front wheels, and by adding or increasing the driving force of the vehicle for the rear wheels. To decrease the wheel slip angle, for example, by promoting the yaw moment (motion) of the vehicle, the slip angle of the vehicle (body) relative to the ground increases, and as a result the slip angle of the wheel decreases. For yaw moment promotion control, the well-known technique of controlling the yawing motion around the vehicle's vertical axis by individually controlling the brake fluid pressure of each wheel 2i can be applied. If we were to implement tire burst risk reduction control without informing the occupants, we could consider controlling the physical quantities that are less sensitive to the rise in tire surface temperature as the burst risk level increases. In other words, the idea is to reduce the burst risk by controlling the physical quantities that are less sensitive to the rise in tire surface temperature while the burst risk level is still low. The sensitivity to the rise in tire surface temperature is highest for wheel load, followed by wheel slip angle and then driving speed. These control quantities can be increased proportionally, for example, as the burst risk level increases, as shown in Figures 9 and 10. As shown in Figure 9, when braking (decelerating) the vehicle to increase the wheel load of the wheels (=front wheels), wheel load increase control is started when the burst risk level exceeds the first threshold. Furthermore, since the upper limit of deceleration that does not cause discomfort to the occupants due to the control of increasing the wheel load of the wheels (=front wheels) is approximately 0.1G, the amount of wheel load increase corresponding to this deceleration is set as the upper limit for reducing the burst risk level by wheel load control, and the value of the burst risk level that can be achieved with that amount of wheel load increase is set as the upper limit of the burst risk level by wheel load control (second threshold).Therefore, as shown in Figure 10, control that reduces the wheel slip angle by yaw moment control, thereby reducing the burst risk level, is initiated when the burst risk level exceeds the second threshold. On the other hand, the level at which the occupant (driver) can respond to yaw moment (motion) control performed by the vehicle is approximately 4° / sec. Therefore, the yaw moment is set as the upper limit for reducing the burst risk level by slip angle reduction control, and the value of the burst risk level that can be achieved by that amount of slip angle reduction is set as the upper limit (third threshold) of the burst risk level by slip angle control. In this case, if the calculated burst risk level exceeds the third threshold, it may be possible to reduce the driving speed without performing wheel load increase control or slip angle reduction control. Note that reducing the driving speed to reduce burst risk is a common method. Furthermore, driving conditions in which the tire surface temperature or the temperature of the inner part of the tire tread reaches the starting temperature of rubber vulcanization are those generally referred to as sporty driving, where the driving speed is high, acceleration and deceleration are frequent and large, and steering is fast and large. In these conditions, the load on the front wheels is greater than that on the rear wheels, so the tire surface temperature of the front wheels tends to be higher than that of the rear wheels.

[0014] Returning to Figure 1, in order to enable the tire surface temperature control device 4, which includes the burst risk control unit 7 and the tire surface temperature calculation unit 6, the vehicle 1 is equipped with a steering angle sensor 21, an acceleration sensor 22, a speed sensor 23, a driving force sensor 24, a road surface temperature sensor 25, an outside air temperature sensor 26, and a TPMS (Tire Pressure Monitoring System) 27. The steering angle sensor 21 detects the steering angle (turning angle) δ of the front wheels 2FR and 2FL, which are the steering wheels of the vehicle 1. The acceleration sensor 22 detects the longitudinal acceleration a generated in the vehicle 1. X and the acceleration a in the width direction (lateral direction) of vehicle 1 Y The speed sensor 23 detects the vehicle's speed V. The drive force sensor 24 detects the drive force and braking force (braking force) F generated in the vehicle 1. XTTL This detects [something].

[0015] The detection information detected by these rudder angle sensors 21, acceleration sensors 22, speed sensors 23, and driving force sensors 24 is acquired by a vehicle state acquisition unit 17 constructed in a processor 5 described later. Further, the road surface temperature sensor 25 detects the road surface temperature T ROAD [°C] of the road surface on which the vehicle 1 travels. For example, it is composed of a non-contact temperature sensor attached to the lower part of the vehicle body of the vehicle 1. In that case, it is arranged at a position facing the road surface on which the vehicle 1 travels. The road surface temperature T detected by this road surface temperature sensor 25 ROAD is acquired by a road surface temperature acquisition unit 18 constructed in a processor 5 described later. The outside air temperature sensor 26 detects the outside air temperature T AIR [°C] outside the vehicle 1. In this embodiment, it is attached to a part facing the inside of the wheel house of the vehicle 1. That is, the outside air temperature sensor 26 in this embodiment detects the temperature around the tire 3 of the wheel 2i in the wheel house. The TPMS 27 detects the air pressure of the tire 3 of each wheel 2i and also detects the internal temperature (tire internal temperature) T INR [°C] of the tire 3. For example, it is attached to the wheel of each wheel 2i. The outside air temperature T detected by the outside air temperature sensor 26 AIR and the tire internal temperature T detected by the TPMS 27 INR are acquired by an environmental temperature acquisition unit 19 constructed in a processor 5 described later. Note that the tire internal temperature T INR is used with the subscript i indicating the position of each wheel 2i attached thereto.

[0016] The tire surface temperature control device 4 has a processor 5 with advanced arithmetic processing capabilities. The processor 5 includes a ROM (Read Only Memory) where programs are stored, a CPU (Central Processing Unit) that executes the programs stored in the ROM, and a RAM (Random Access Memory) that functions as an accessible storage device. The processor 5 is equipped with a tire surface temperature calculation unit 6 and a burst risk control unit 7 as functional units. The tire surface temperature calculation unit 6 includes a vehicle state acquisition unit 17, a heat generation amount calculation unit 8, a previous temperature acquisition unit 20, a road surface temperature acquisition unit 18, an ambient temperature acquisition unit 19, a heat dissipation amount calculation unit 9, a temperature change amount calculation unit 10, and a surface temperature calculation unit 11. The heat dissipation amount calculation unit 9 further includes a first heat dissipation amount calculation unit 9a and a second heat dissipation amount calculation unit 9b. The burst risk control unit 7 includes a turning duration calculation unit 28, a wheel load acquisition unit 29, a surface temperature coefficient calculation unit 30, a road surface friction coefficient acquisition unit 31, a tire friction coefficient calculation unit 32, a burst risk level calculation unit 33, a burst suppression control determination unit 34, and a burst suppression control command unit 35. These functional units operate when the CPU executes a program stored in ROM within the processor 5.

[0017] The following describes how the tire surface temperature calculation unit 6 estimates the surface temperature of the tire 3. The vehicle state acquisition unit 17 of the tire surface temperature calculation unit 6 acquires the steering angle (turning angle) δ of the vehicle 1 detected by the steering angle sensor 21, and the longitudinal acceleration (longitudinal acceleration) a of the vehicle 1 detected by the acceleration sensor 22. X and the acceleration (lateral acceleration) in the width direction (lateral direction) of vehicle 1 a Y , the driving speed V of vehicle 1 detected by speed sensor 23, and the braking force F detected by drive force sensor 24 XTTL The magnitude of the vehicle state is obtained. The vehicle state acquisition unit 17 then outputs this information as vehicle state information to the heat generation amount calculation unit 8. The heat generation amount calculation unit 8 calculates the heat generation amount of the tires 3 of each wheel 2i based on the vehicle state information input from the vehicle state acquisition unit 17. The heat generation amount is calculated as follows. First, the heat generation amount calculation unit 8 calculates the vertical load (wheel load) of each wheel 2i based on the vertical acceleration and lateral acceleration. In the calculation, as shown in Figure 2a, the vertical acceleration aX [m / s 2 Change in vertical load ΔF due to ] Z-X [N] is calculated according to the following formula. In the formula, M[kg] is the mass of vehicle 1, L[m] is the wheelbase (farthest axle distance) of vehicle 1, H CG [m] is the height of the center of gravity of vehicle 1. Similarly, as shown in Figure 2b, the lateral acceleration a Y [m / s 2 Change in vertical load ΔF due to ] Z-Y [N] is calculated according to the following two formulas. In the formulas, D[m] is the tread of vehicle 1 (distance between the centers of the contact surfaces of the left and right wheels).

[0018]

number

[0019] Using these vertical load changes, the vertical load of each wheel 2i, i.e., the front right wheel load F, is calculated. ZFR [N], front left wheel load F ZFL [N], rear right wheel load F ZRR [N], rear left wheel load F ZRL [N] is calculated according to the following equations 3 to 6. Note that in the equations, L R [m] is the distance between the center of gravity and the rear axle of vehicle 1, L F [m] is the distance between the center of gravity and the front axle of vehicle 1.

[0020]

number

[0021] Furthermore, the heat generation calculation unit 8 calculates the total lateral force F of the vehicle 1 (all wheels 2i). YTTL [N] is distributed to each wheel 2i, and the lateral force of each wheel 2i, i.e., the lateral force F of the front right wheel, is distributed in this manner. YFR [N], Front left wheel lateral force F YFL [N], Rear right wheel lateral force F YRR [N], rear left wheel lateral force F YRL [N] is calculated according to equations 7-10 below. Note that the total lateral force F of vehicle 1 YTTL [N] represents the mass M [kg] of vehicle 1 and the lateral acceleration a Y [m / s 2It is the product of ].

[0022]

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[0023] Furthermore, the heat generation calculation unit 8 calculates the braking and driving force F of the vehicle 1 (all wheels 2i). XTTL [N] is distributed to each wheel 2i, and the longitudinal force of each wheel 2i, i.e., the longitudinal force F of the front right wheel, is distributed in this manner. XFR [N], front left wheel longitudinal force F XFL [N], rear right wheel longitudinal force F XRR [N], rear left wheel longitudinal force F XRL [N] is calculated according to the following 11 equations. In the equations, DR is the ratio of braking and driving force distribution to each wheel 2i, and the subscript i represents the position of the wheel 2i, i.e., FR for front right, FL for front left, RR for rear right, and RL for rear left.

[0024]

number

[0025] The heat generation calculation unit 8 then calculates the vertical force F of each wheel 2i. Xi [N] and vertical load F Zi Based on [N], the longitudinal heat storage coefficient (which is also the heat capacity) W of the tire 3 of each wheel 2i is determined by referring to a pre-stored map. Xi [N·m / ℃] is obtained. Similarly, the heat generation calculation unit 8 calculates the lateral force F of each wheel 2i. Yi [N] and vertical load F Zi Based on [N], the lateral heat storage coefficient (heat capacity) W of the tire 3 of each wheel 2i is determined by referring to a pre-stored map. Yi Obtain the [N·m / ℃] longitudinal heat storage coefficient of the tire 3 of each wheel 2i (hereinafter referred to as the tire longitudinal heat storage coefficient W). Xi and the lateral heat storage coefficient (tire lateral heat storage coefficient) W of the tire 3 of each wheel 2i YiThe map used to obtain the tire longitudinal heat storage coefficient W is a map created to reflect the fact that the heat generation amount QG of the tire 3 saturates when a large load (vertical load, longitudinal force and lateral force applied to the tire 3) greater than a predetermined value is applied to each tire 3. Therefore, the tire longitudinal heat storage coefficient W obtained by the heat generation amount calculation unit 8 is a map created to reflect the fact that the heat generation amount QG of the tire 3 saturates when a large load (vertical load, longitudinal force and lateral force applied to the tire 3) is applied to each tire 3. Xi and the lateral heat storage coefficient of the tire W Yi The heat generated by tire 3 QG increases with increasing load, but the rate of increase gradually decreases. i (See Figure 3) This value is affected by the inflection point. Note that, if the tires 3 of each wheel 2i have clear and identical specifications, as described later for the original tires, then the longitudinal heat storage coefficient W of each tire 3 is... Xi and the lateral heat storage coefficient W Yi Although this is the same for all wheels 2i, as will be described later, in this embodiment, in order to deal with unknown tires (different types of tires) whose specifications for each wheel 2i are unknown, the longitudinal heat storage coefficient W of the tire 3 is used. Xi and the lateral heat storage coefficient W Yi The subscript i is assigned to each wheel 2i to indicate its position.

[0026] Next, the heat generation calculation unit 8 calculates the heat generation QG of the tires 3 of each wheel 2i. i To calculate this, based on the steering angle δ and travel speed V of vehicle 1, for example, from a two-wheeled model, the longitudinal slip speed V of each wheel 2i (tire 3) is used. SLPXi and lateral slip speed V SLPYi The vertical slip velocity V is calculated as shown in Figure 3. SLPXi and lateral slip speed V SLPYi and the longitudinal force F of each wheel 2i (tire 3) Xi and lateral force F Yi and the longitudinal heat storage coefficient of the tire W Xi and the lateral heat storage coefficient of the tire W Yi Using the following formula 12, the amount of heat generated between the tire 3 of each wheel 2i and the road surface (tire heat generation) QG is calculated. i Calculate [℃ / s]. Here, tire heat generation QG i As is clear from the units, the calculated tire heat output QG iThis represents the increase in tire temperature per unit time, or what can be called the tire temperature increase rate.

[0027]

number

[0028] Next, the previous temperature acquisition unit 20 shown in Figure 1, as will be described later, takes the surface temperature of the tire 3 of each wheel 2i calculated by the surface temperature calculation unit 11 and returns it to the previous surface temperature (previous tire surface temperature) T of the tire 3 of each wheel 2i. 0i The temperature is obtained as [°C]. Note that the previous temperature acquisition unit 20 is the ambient temperature T detected by the ambient temperature sensor 26 and acquired by the ambient temperature acquisition unit 19. AIR The data from the previous tire surface temperature T 0i The initial value is obtained via CAN. That is, the previous tire surface temperature T 0i The initial value is the ambient temperature T AIR This is the previous tire surface temperature T obtained by the previous temperature acquisition unit 20. 0i Using this, the first heat dissipation amount calculation unit 9a in the heat dissipation amount calculation unit 9 calculates the first heat dissipation amount (first tire heat dissipation amount) QD1 of the tires 3 of each wheel 2i. i Calculate the [℃ / s]. First tire heat dissipation QD1 i As shown in Figure 3, this is the amount of heat dissipated from the tires 3 of each wheel 2i to the road surface, and the road surface temperature T obtained by the road surface temperature acquisition unit 18. ROAD The following 13 equations are used to obtain the result. Note that the road surface heat dissipation coefficient κ1 [1 / s] in the equation may be set to be larger as the road surface temperature decreases. In addition, the second heat dissipation amount calculation unit 9b in the heat dissipation amount calculation unit 9 uses the previous tire surface temperature T 0i Using this, the second heat dissipation amount (second tire heat dissipation amount) QD2 of the tire 3 of each wheel 2i is calculated. i Calculate the [℃ / s]. This is the heat dissipation of the second tire QD2. i This refers to the ambient temperature T obtained by the ambient temperature acquisition unit 19. AIR and tire internal temperature T INRiBased on the following formula (14), as shown in FIG. 3, it includes the heat dissipation amount QD21 (the first term on the right side of formula (14)) radiated from the tire 3 of each wheel 2i to the outside air and the heat dissipation amount QD22 (the second term on the right side of formula (14)) radiated from the tire 3 to the air inside the tire. Here, the outside air heat dissipation coefficient κ2 in the formula is set to be larger as the outside air temperature T AIR is smaller. Also, the internal heat dissipation coefficient κ3 in the formula may be set to be larger as the internal temperature T INRi of the tire is smaller.

[0029]

Equation

[0030] Here, as is clear from the units of the first tire heat dissipation amount QD1 i and the second tire heat dissipation amount QD2 i , the calculated first tire heat dissipation amount QD1 i and the second tire heat dissipation amount QD2 i are the temperature decrease amount of the tire 3 per unit time, that is, what can be called the tire temperature decrease rate. Note that the value obtained by multiplying the difference value between the previous tire surface temperature T 0i and the outside air temperature T AIR by the outside air heat dissipation coefficient κ2, that is, only the first term on the right side of formula (14) may be used as the second tire heat dissipation amount QD2 i . Similarly, the value obtained by multiplying the difference value between the previous tire surface temperature T 0i and the internal temperature T INRi of the tire by the internal heat dissipation coefficient κ3, that is, only the second term on the right side of formula (14) may be used as the second tire heat dissipation amount QD2 i . And the temperature change amount calculation unit 10 subtracts the first tire heat dissipation amount QD1 i and the second tire heat dissipation amount QD2 i from the tire heat generation amount QG i and calculates the temperature change amount (tire temperature change amount) dT i / dt [℃ / s] of the surface temperature of the tire 3 of each wheel 2i according to the following formula (15). Also, if formula (12) is substituted into the tire heat generation amount QG i in formula (15), the following formula (16) is obtained. Here, the tire temperature change amount dT iAs is clear from the unit / dt, the calculated tire temperature change amount dT i / dt represents the rate of change in tire temperature 3 per unit time, or the tire temperature change rate. The surface temperature calculation unit 11 in Figure 1 calculates the previous tire surface temperature T 0i and tire temperature change dT i Based on / dt, the surface temperature of each wheel 2i tire 3 (tire surface temperature T) i Calculate.

[0031]

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[0032] The calculation process in the above-mentioned functional unit is shown in the flowchart of Figure 4. In the calculation process according to this flowchart, first in step S1, the heat generation unit 8 calculates the vertical load F of each wheel 2i according to equations 1 to 6 above. Zi Next, in step S2, the heat generation calculation unit 8 calculates the longitudinal force F of each wheel 2i according to equations 7 to 11 above. Xi and lateral force F Yi Next, in step S3, the heat generation calculation unit 8 calculates the vertical load F of each wheel 2i by referring to the map above. Zi and vertical force F Xi and lateral force F Yi The heat storage coefficient W of the tire 3 of each wheel 2i corresponds to X , W Y Next, in step S4, the heat generation calculation unit 8 calculates the slip speed V of each wheel 2i. SLPXi , V SLPYi Next, in step S5, the heat generation calculation unit 8 calculates the longitudinal force F of each wheel 2i according to the above equation 12. Xi and lateral force F Yi The heat storage coefficient W of the tire 3 of each wheel 2i X , W Y , slip speed V of each wheel 2i SLPXi , V SLPYi QG of tire heat generation for each wheel 2i according to the corresponding value i Next, in step S6, the road surface temperature acquisition unit 18 calculates the road surface temperature T ROADNext, in step S7, the ambient temperature acquisition unit 19 obtains the outside air temperature T AIR Next, in step S8, the ambient temperature acquisition unit 19 obtains the internal tire temperature T of each wheel 2i. INRi The following is obtained. Here, the processes in steps S6 to S8 may be executed in any order, or they may be executed simultaneously. Also, either step S7 or step S8 may be performed alone. Next, in step S9, the heat dissipation amount calculation unit 9 obtains the previous tire surface temperature T 0i and road surface temperature T ROAD Using the above formula 13, the heat dissipation QD1 of the first tire of each wheel 2i i In addition to calculating the previous tire surface temperature T 0i and outside air temperature T AIR and tire internal temperature T INRi Using the above formula 14, the heat dissipation QD2 of the second tire of each wheel 2i i The following is calculated. As mentioned above, the heat dissipation amount of the second tire QD2 i This may be only the first term on the right-hand side of the above equation 14, or only the second term. Next, in step S10, the temperature change amount calculation unit 10 calculates the tire heat generation amount QG i , 1st tire heat dissipation QD1 i , and the heat dissipation of the second tire QD2 i Using the above equations 15 to 16, the change in tire temperature dT of each wheel 2i i / dt is calculated. Then, in step S11, the surface temperature calculation unit 11 calculates the previous tire surface temperature T of each wheel 2i. 0i and tire temperature change dT i Tire surface temperature T using / dt i Calculate.

[0033] Next, the calculation process performed in the burst risk control unit 7 from the turning duration calculation unit 28 to the burst suppression control command unit 35 in Figure 1 will be explained using the flowchart in Figure 6. This calculation process is performed, for example, by a timer interrupt process with a predetermined sampling period. In this calculation process, first, in step S21, the turning duration calculation unit 28 determines whether or not the vehicle is turning. If the vehicle is turning, it proceeds to step S22; otherwise, it proceeds to step S32. In step S22, the elapsed time since the previous calculation (= sampling period) is added to calculate the turning duration, and then it proceeds to step S23. On the other hand, in step S32, the turning duration is reset and then returned. In step S23, the surface temperature coefficient calculation unit 30 reads the tire surface temperature of each wheel 2i calculated by the surface temperature calculation unit 11. Next, it proceeds to step S24, where the surface temperature coefficient of the tire 3 of each wheel 2i is calculated using the tire surface temperature of each wheel 2i and the turning duration, by searching the control map in Figure 7. Next, the process moves to step S25, where the wheel load acquisition unit 29 reads the wheel load of each wheel 2i calculated by the heat generation calculation unit 8. Next, the process moves to step S26, where the road surface friction coefficient acquisition unit 31 reads the road surface friction coefficient from the electric power steering device of the driving control device 36. Next, the process moves to step S27, where the tire friction coefficient calculation unit 32 calculates the tire friction coefficient of each wheel 2i by multiplying the road surface friction coefficient by a coefficient corresponding to the ratio of the wheel loads of each wheel 2i. Next, the process moves to step S28, where the burst risk level calculation unit 33 calculates the burst risk level from the wheel load of each wheel 2i and the product of the tire surface temperature and the surface temperature coefficient. Next, the process moves to step S29. The burst suppression control determination unit 34 evaluates the burst risk of the tire 3 of each wheel 2i based on the burst risk level calculated by the burst risk level calculation unit 33. Using the control maps in Figures 9 and 10, it determines the target physical quantity (suppression control mode in the figures) to be controlled to reduce the burst risk of each wheel 2i based on the burst risk level of each wheel 2i, and simultaneously calculates the control amount. In the burst risk evaluation, a higher burst risk level indicates a higher burst risk for the tire 3 of that wheel 2i.Next, the process moves to step S30, where the burst suppression control command unit 35 outputs a control command corresponding to the controlled physical quantity (burst suppression control mode in the figure) that reduces the burst risk to the hydraulic controller 12b and / or drive controller 13a, and then returns to its original position. The brake hydraulic pressure control that enhances the yaw moment applies, for example, the well-known yawing motion control that first applies braking force to the rear wheel on the inside of the turn, and then applies braking force to the rear wheel on the outside of the turn, in order to suppress the sideslip of the front wheel to the outside of the turn.

[0034] According to this calculation process, a surface temperature coefficient representing the risk of reduced rigidity of the tire structure is set from the tire surface temperature and turning duration. The burst risk level of the tire 3 for each wheel 2i is calculated from the product of this surface temperature coefficient, the friction coefficient of each wheel 2i, and the wheel load. A higher burst risk level indicates a greater burst risk for the tire 3, so the burst risk of the tire 3 for each wheel 2i is evaluated using this burst risk level. As a result of this evaluation of the burst risk level, if the burst risk level is between the first threshold and the second threshold, wheel load increase control for the corresponding wheel 2i is selected; if it is between the second threshold and the third threshold, slip angle reduction control for the corresponding wheel 2i is selected; and if it is above the third threshold, travel speed reduction control is selected. At the same time, the control amount for each control is set according to the burst risk level, and a control command corresponding to the physical quantity to be controlled is output to the hydraulic controller 12b and / or drive controller 13a. The slip angle reduction control of the wheel 2i is performed by yaw moment enhancement control of the vehicle. This burst risk reduction control system allows for a longer driving time before deceleration control, a common burst risk reduction method, is initiated. This also increases the driving time during which burst risk reduction control can be performed, and reduces the discomfort experienced by the occupants during burst risk reduction control.

[0035] Thus, in this embodiment, when the risk of a tire 3 mounted on a wheel 2i of a vehicle 1 bursting is evaluated by the processor 5, the tire surface temperature is calculated, and based on the calculated tire surface temperature, a surface temperature coefficient representing the risk of decreased rigidity of the tire structure due to the rise in the surface temperature of the tire 3 is calculated, and based on the shear force acting on the surface of the tire 3 and the surface temperature coefficient, a burst risk level is calculated as an evaluation index for the risk of the tire bursting, and the higher the burst risk level, the greater the risk of the tire bursting. This makes it possible to appropriately evaluate the burst risk of the tire 3, such as tread delamination. Furthermore, by representing the burst risk level as the product of the surface temperature coefficient and the shear force acting on the surface of tire 3, it becomes possible to appropriately reflect the physical properties of tire 3, such as its heat transfer characteristics, in the burst risk. Furthermore, by setting a surface temperature coefficient that increases with longer turning duration and / or with higher tire surface temperature, the risk of tire 3 bursting, such as tread delamination, can be appropriately evaluated. Furthermore, by calculating the surface temperature coefficient according to a map that reflects the physical properties of tire 3, the physical properties of tire 3, such as its heat transfer characteristics, can be appropriately reflected in the burst risk. Furthermore, by using the frictional force of tire 3, which is the product of the tire friction coefficient and the wheel load of wheel 2i, as the shear force acting on the surface of tire 3, it becomes possible to concisely and appropriately evaluate the burst risk of tire 3.

[0036] Furthermore, if the calculated burst risk level is above a predetermined value (first threshold), the risk of tire 3 bursting can be reduced by controlling the physical quantities of the vehicle that contribute to the sensitivity of the surface temperature rise of tire 3, thereby reducing the risk of tire 3 bursting without causing discomfort to the occupants (driver). Furthermore, as the burst risk level increases, the risk of tire 3 bursting is reduced by controlling the wheel load on wheel 2i, the slip angle of wheel 2i, and the driving speed in that order, thereby reducing the risk of tire 3 bursting without causing discomfort to the occupants (driver). Furthermore, by controlling the wheel load increase when the burst risk level is above the first threshold but below the second threshold, controlling the slip angle decrease when it is above the second threshold but below the third threshold, and controlling the driving speed decrease when it is above the third threshold, the burst risk of tire 3 can be reduced without causing discomfort to the occupants (drivers), and more effective burst risk reduction control can be implemented for excessively high burst risk levels. Furthermore, by controlling the reduction of the slip angle of wheel 2i through the enhancement of the yaw moment of vehicle 1, it becomes possible to easily and reliably reduce the risk of tire 3 bursting. Furthermore, by controlling the increase in wheel load within a range that does not cause discomfort to the occupants, the risk of tire 3 bursting can be reduced while the burst risk level is still low, without causing discomfort to the occupants. Furthermore, by controlling the reduction of the slip angle within a range that the driver can respond to, the risk of tire 3 bursting can be reduced while the burst risk level is still small, without causing discomfort to the occupants. Although the tire burst risk assessment and reduction system according to the embodiment has been described above, the present invention is not limited to the configuration described in the above embodiment, and various modifications are possible within the scope of the gist of the present invention. [Explanation of Symbols]

[0037] 1...Vehicle, 2i...Wheel, 3...Tire, 4...Tire surface temperature control device, 5...Processor (arithmetic processing unit), 6...Tire surface temperature calculation unit, 7...Burst risk control unit, 8...Heat generation amount calculation unit, 9...Heat dissipation amount calculation unit, 10...Temperature change amount calculation unit, 11...Surface temperature calculation unit, 28...Turning duration calculation unit, 29...Wheel load acquisition unit, 30...Surface temperature coefficient calculation unit, 31...Road surface friction coefficient acquisition unit, 32...Tire friction coefficient calculation unit, 33...Burst risk level calculation unit, 34...Burst suppression control determination unit, 35...Burst suppression control command unit

Claims

1. A burst risk assessment method for evaluating the risk of a tire mounted on a vehicle's wheel bursting, using a computing device, A tire surface temperature calculation step for calculating the surface temperature of the tire, A surface temperature coefficient calculation step, which calculates a surface temperature coefficient representing the risk of reduced rigidity of the tire structure due to an increase in the surface temperature of the tire, based on the calculated surface temperature of the tire, A burst risk level calculation step, which calculates a burst risk level as an evaluation index for the risk of the tire bursting, based on the shear force acting on the surface of the tire and the surface temperature coefficient, A burst risk evaluation method characterized by comprising: a burst risk evaluation step of evaluating that the greater the burst risk level, the greater the risk of the tire bursting.

2. The burst risk level evaluation method according to claim 1, characterized in that the burst risk level is expressed as the product of the surface temperature coefficient and the shear force.

3. The system includes a turning duration calculation step that calculates the duration of the turning motion of the vehicle as the turning duration, The burst risk level evaluation method according to claim 1, characterized in that the surface temperature coefficient calculation step sets a surface temperature coefficient that is larger the longer the turning duration and / or larger the higher the surface temperature of the tire, based on the turning duration and the surface temperature of the tire.

4. The burst risk level evaluation method according to claim 3, characterized in that the surface temperature coefficient calculation step calculates the surface temperature coefficient according to a map set according to the turning duration and the surface temperature of the tire, in which the surface temperature coefficient reflects the physical properties of the tire.

5. The burst risk level evaluation method according to claim 1, wherein the burst risk level calculation step comprises a tire friction coefficient calculation step for calculating the friction coefficient of the tire and a wheel load acquisition step for acquiring the wheel load of each wheel, and the tire friction force, which is the product of the tire friction coefficient and the wheel load of the wheel, is used as the shear force acting on the surface of the tire.

6. A burst risk reduction method characterized by comprising a burst risk reduction step, in which, when the burst risk level calculated by the burst risk evaluation method described in claim 1 is equal to or greater than a predetermined value, the method controls a physical quantity of the vehicle that contributes to the sensitivity of the tire's surface temperature rise to reduce the risk of the tire bursting.

7. The burst risk reduction method according to claim 6, wherein the physical quantities are the wheel load of each wheel, the slip angle of each wheel, and the running speed, and the burst risk reduction step controls, in order, an increase in the wheel load, a decrease in the slip angle, and a decrease in the running speed as the burst risk level increases, thereby reducing the risk of the tire bursting.

8. The burst risk reduction method according to claim 7, characterized in that the burst risk reduction step involves controlling the increase of the wheel load when the burst risk level is greater than or equal to a first threshold and less than a second threshold, controlling the decrease of the slip angle when the burst risk level is greater than or equal to a second threshold and less than a third threshold, and controlling the decrease of the travel speed when the burst risk level is greater than or equal to a third threshold.

9. The burst risk reduction method according to claim 7, characterized in that the control of reducing the slip angle is performed by controlling the yaw moment of the vehicle.

10. The burst risk reduction method according to claim 7, characterized in that the control of increasing the wheel load is performed within a range that does not cause discomfort to the occupants.

11. The burst risk reduction method according to claim 7, characterized in that the slip angle reduction control is performed within a range that the driver can respond to.

12. A burst risk evaluation device that uses a computing device to evaluate the risk of a tire mounted on a vehicle's wheel bursting, The burst risk evaluation device is characterized in that the processing unit calculates the surface temperature of the tire, calculates a surface temperature coefficient representing the risk of a decrease in the rigidity of the tire structure due to a rise in the surface temperature of the tire based on the calculated surface temperature of the tire, calculates a burst risk level as an evaluation index for the risk of the tire bursting based on the shear force acting on the surface of the tire and the surface temperature coefficient, and evaluates that the greater the burst risk level, the greater the risk of the tire bursting.

13. A burst risk reduction device characterized in that, when the burst risk level calculated by the burst risk evaluation device according to claim 12 is greater than or equal to a predetermined value, it controls a physical quantity of the vehicle that contributes to the sensitivity of the tire's surface temperature rise to reduce the risk of the tire bursting.

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