Tire diameter calculation system

Abstract

To allow a tire diameter to be calculated appropriately.SOLUTION: A tire diameter calculation system of the present invention includes: a distance sensor 13 that measures a distance between a road surface and a vehicle body by using irradiation of electromagnetic waves; a stroke sensor 14 that measures a stroke of a suspension 30; and a control unit 11 that calculates a diameter of a mounted tire based on the distance measured by the distance sensor 13 and the stroke measured by the stroke sensor 14. By taking into account the stroke measured by the stroke sensor 14, it is possible to appropriately calculate the tire diameter regardless of a loading situation.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a tire diameter calculation system. [Background technology]

[0002] It has been known that the vehicle speed is calculated based on the diameter of the tires mounted on the vehicle and the rotational speed of the tires. However, if tires of a different diameter are replaced and mounted on such a vehicle, the vehicle speed cannot be calculated with high accuracy.

[0003] Patent Document 1 discloses a tire wear estimation method that estimates the degree of tire wear using the amount of deflection, which is the difference between the tire radius, which is the radius of the tire when no load is applied, and the effective radius, which is the radius of the tire when in motion (the distance between the axle and the road surface).In Patent Document 1, a distance sensor is installed on the vehicle on which the tire is mounted to measure the distance from the vehicle to the road surface, and the measured distance is converted into the distance between the axle and the road surface to calculate the effective radius of the tire. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 7319940 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the method of calculating tire diameter disclosed in Patent Document 1, the calculated tire diameter is affected by the vehicle's load status, such as the number of passengers on board and the amount of luggage carried. That is, if the load is heavy, the distance sensor will measure a smaller distance between the vehicle and the road surface, and if the load is light, the distance sensor will measure a larger distance between the vehicle and the road surface, resulting in a calculated tire diameter that differs from the actual tire diameter. Therefore, the conventional method of calculating tire diameter has a problem in that it is not possible to calculate the tire diameter appropriately.

[0006] The present invention has been made in consideration of the above-mentioned problems, and an object of the present invention is to make it possible to appropriately calculate the tire diameter. [Means for solving the problem]

[0007] The tire diameter calculation system of the present invention is characterized by having a distance sensor that measures the distance between the road surface and the vehicle body by irradiating electromagnetic waves, a stroke sensor that measures the suspension stroke, and a control unit that calculates the diameter of the tire mounted on the vehicle based on the distance measured by the distance sensor and the stroke measured by the stroke sensor. [Effects of the Invention]

[0008] According to the present invention, the tire diameter can be calculated appropriately. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a vehicle equipped with a tire diameter calculation system. [Figure 2] 1A and 1B are schematic diagrams showing the state of a vehicle before and after tire replacement. [Figure 3] 10A and 10B are schematic diagrams showing the state of a vehicle when the loading situation has changed; [Figure 4] 10 is a flowchart illustrating an example of a process for calculating a tire diameter. DETAILED DESCRIPTION OF THE INVENTION

[0010] The tire diameter calculation system according to the present invention comprises a distance sensor 13 that measures the distance between the road surface and the vehicle body by irradiating electromagnetic waves, a stroke sensor 14 that measures the stroke of the suspension 30, and a control unit 11 that calculates the diameter of the mounted tire based on the distance measured by the distance sensor 13 and the stroke measured by the stroke sensor 14. By taking into account the stroke measured by the stroke sensor 14, it is possible to appropriately calculate the tire diameter regardless of the loading situation. [Example]

[0011] A tire diameter calculation system according to the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of a vehicle 1 equipped with a tire diameter calculation system. The tire diameter calculation system is installed in a vehicle 1 in which a driver rides. The vehicle 1 in which the tire diameter calculation system is installed is equipped with devices that are equipped in general vehicles, and illustrations and descriptions of these devices will be omitted as appropriate.

[0012] The vehicle 1 according to the embodiment includes a vehicle body 10, tires 20, and a suspension 30. The vehicle body 10 comprises a body that forms the skeleton of the vehicle body, a drive source that drives the vehicle 1, a power transmission device that transmits power from the drive source to tires 20, a control unit 11 that electrically controls the drive source and the vehicle body 10, and a sensor unit 12.

[0013] The control unit 11 is, for example, an ECU (Electronic Control Unit). The control unit 11 has a CPU, ROM, RAM, etc. as a hardware configuration. The ROM stores programs and predetermined information for controlling the drive source, etc. The RAM is a work memory that temporarily stores programs and data. The CPU reads out the programs stored in the ROM, expands them into the RAM, and executes them to control the drive source, etc.

[0014] The control unit 11 also calculates the diameter of the tire 20 based on information measured by the sensor unit 12, etc. A specific method for calculating the diameter of the tire 20 will be described later. Furthermore, the control unit 11 calculates the vehicle speed of the vehicle 1 based on the calculated information on the diameter of the tire 20 and information on the rotational speed of the tire measured by the wheel speed sensor 15, and outputs the calculated vehicle speed information by displaying or storing it. The control unit 11 is not limited to being configured by one ECU, but may be configured by a plurality of ECUs working together. Also, the control unit that controls the drive source and the control unit that calculates the diameter of the tire 20 are not limited to being the same control unit, but may be different control units.

[0015] The sensor unit 12 measures various conditions of the vehicle 1. Specifically, the sensor unit 12 includes a distance sensor 13, a stroke sensor 14, a wheel speed sensor 15, an acceleration sensor 16, and the like.

[0016] The distance sensor 13 measures the distance between the vehicle body 10 and the road surface by irradiating electromagnetic waves. The distance sensor 13 transmits information about the measured distance to the control unit 11. The distance sensor 13 may be, for example, a millimeter wave sensor or a laser sensor. The stroke sensor 14 measures the stroke of the suspension 30. The stroke sensor 14 transmits information about the measured stroke to the control unit 11. The wheel speed sensor 15 measures the rotation speed of the tire 20. The wheel speed sensor 15 transmits information on the measured rotation speed of the tire to the control unit 11. The acceleration sensor 16 measures the inclination of the vehicle body 10. The acceleration sensor 16 transmits information on the measured inclination of the vehicle body 10 to the control unit 11.

[0017] The tires 20 are in contact with the road surface and transmit power from a drive source to the road surface to drive the vehicle 1. The tires 20 are detachable from the vehicle body 10. Therefore, the occupants of the vehicle 1 can replace and mount tires 20 with tires 20 of a different diameter from the tires 20 that were mounted on the vehicle body 10 at the time of initial manufacture of the vehicle 1.

[0018] The suspension 30 extends in a substantially vertical direction and connects the vehicle body 10 and the tire 20. The suspension 30 includes a coil spring 31 that absorbs impacts and vibrations, and a shock absorber that suppresses vibrations of the vehicle body 10. One end of the suspension 30 is connected to the underside of the vehicle body 10, and the other end is connected to a hub carrier, lower arm, or the like that is located close to the axle (center) of the tire 20. Note that the shock absorber of the suspension 30 is omitted from the illustration in FIG. 1.

[0019] Next, a method for calculating the diameter of the tire 20 mounted on the vehicle body 10 in the vehicle 1 configured as described above will be described. FIG. 2 is a schematic diagram showing the state of a vehicle before and after tire replacement, and the loading situation of the vehicle is the same before and after tire replacement.

[0020] FIG. 2(a) is a diagram showing a state in which a tire with a small diameter (radius R0) is mounted, and distance H0 is measured by distance sensor 13 as the distance from the vehicle body to the road surface. On the other hand, FIG. 2(b) shows a state in which tires with a larger diameter (radius R1) have been replaced and mounted, and distance sensor 13 measures distance H1 as the distance from the vehicle body to the road surface.

[0021] Here, since the vehicle's loading conditions are the same before and after tire replacement, if the tire diameter changes before and after tire replacement, the vehicle height and ground clearance also increase or decrease by the same amount. In other words, the difference in tire diameter before and after tire replacement is directly reflected as the difference in the distance from the vehicle body to the road surface. Therefore, if the vehicle's loading conditions are the same, the radius R1 of the replaced tire can be calculated using the radius R0 of the tire before replacement, the distance H0 from the vehicle body to the road surface before replacement, and the distance H1 from the vehicle body to the road surface after replacement.

[0022] FIG. 3 is a schematic diagram showing the state of a vehicle when the loading situation has changed, and the tires (tire diameter) are the same before and after the change in loading situation.

[0023] FIG. 3(a) shows a state in which tires with a radius of R0 are mounted and no load is carried, and the distance sensor 13 measures a distance H0 as the distance from the vehicle body to the road surface. On the other hand, FIG. 3(b) is a diagram showing a state in which tires with a radius R0 are mounted and a load is loaded, and distance sensor 13 measures distance H2 as the distance from the vehicle body to the road surface.

[0024] In this case, even though the tires are the same, the vehicle height and ground clearance change when the vehicle goes from an unladen state to a loaded state, causing the distance from the vehicle body to the road surface to change. Therefore, when the loading situation changes, the distance from the vehicle body to the road surface measured by distance sensor 13 before and after tire replacement also reflects the change in loading situation, so the diameter of the replaced tire cannot be calculated based only on the information on the distance from the vehicle body to the road surface measured by distance sensor 13.

[0025] In this embodiment, the change in height due to the loading condition is obtained using the stroke of the suspension 30 measured by the stroke sensor 14. In the unladen state of FIG. 3( a ), the stroke sensor 14 measures a distance S 0 as the stroke of the suspension 30 . On the other hand, in the state where a load is loaded as shown in FIG. 3(b), the stroke sensor 14 measures the distance S2 as the stroke of the suspension 30. Therefore, since the difference between the distance S0 and the distance S2 measured by the stroke sensor 14 is due to the change in the loading condition, by also using the difference in the distance measured by the stroke sensor 14, the tire diameter after replacement can be calculated without being affected by the loading condition.

[0026] Specifically, the radius of the tire fitted to the vehicle 1 at the initial manufacturing stage is defined as Ra, the stroke measured by the stroke sensor 14 as Sa (first stroke), and the distance measured by the distance sensor 13 as Ha (first distance). Next, the radius of the tire fitted after a tire change is defined as Rb, the stroke measured by the stroke sensor 14 as Sb (second stroke), and the distance measured by the distance sensor 13 as Hb (second distance).

[0027] At this time, the radius Rb of the tire fitted after tire replacement can be calculated by the following formula (1). Rb= Ra+(Hb-Ha)-(Sb-Sa)=Ra+Hb+Sa-Ha-Sb (1) The data of the radius Ra of the tires mounted on the vehicle 1 at the initial stage of manufacture, the stroke Sa of the suspension 30, and the distance Ha are stored in advance in the control unit 11.

[0028] Next, the process of calculating the diameter of the tire 20 by the control unit 11 using the above-mentioned formula (1) will be described with reference to the flowchart in Fig. 4. The flowchart in Fig. 4 starts when the control unit 11 starts up and executes a program. In S10, the control unit 11 determines whether the vehicle 1 is stopped. Specifically, the control unit 11 determines whether the vehicle 1 is stopped based on information about the rotational speed measured by the wheel speed sensor 15. If the vehicle 1 is stopped (if the rotational speed is 0), the process proceeds to S11. On the other hand, if the vehicle 1 is not stopped (if the rotational speed is not 0), the process returns to S10 and waits until the vehicle 1 stops. The reason for waiting for the vehicle 1 to stop in this way is that when the vehicle 1 is moving, the stroke of the suspension 30 varies regardless of the loading situation, making it impossible to properly calculate the tire diameter.

[0029] In S11, the control unit 11 determines whether the vehicle 1 is tilted. Specifically, the control unit 11 determines whether the vehicle 1 is tilted based on information about the tilt of the vehicle body 10 measured by the acceleration sensor 16. For example, if the road surface on which the vehicle 1 is stopped is not a horizontal, flat road but a sloped road, the vehicle 1 will stop tilted. If the vehicle 1 is not tilted, the process proceeds to S12. On the other hand, if the vehicle 1 is tilted, the process returns to S10 and waits until the vehicle 1 is stopped and not tilted. The reason for waiting until the vehicle 1 is not tilted in this way is that if the vehicle 1 is tilted, the stroke of the suspension 30 will fluctuate regardless of the loading situation, making it impossible to properly calculate the tire diameter.

[0030] In S12, the control unit 11 obtains by reading out each piece of information stored in advance: the radius Ra of the tire mounted at the first point in time, the stroke Sa (first stroke) measured by the stroke sensor 14, and the distance Ha (first distance) measured by the distance sensor 13. Here, if the tire has never been replaced with a tire of a different diameter, the first point in time refers to the initial manufacturing period. The tire radius Ra, stroke Sa, and distance Ha at the initial manufacturing period are stored in advance in the control unit 11 when the vehicle 1 is manufactured. On the other hand, if the tire has been replaced with a tire of a different diameter, the tire radius Ra, stroke Sa, and distance Ha at the first point in time correspond to the information acquired in S13 and S14 (described later) when the flowchart of FIG. 4 is executed immediately after the tire has been replaced.

[0031] In S13, the control unit 11 acquires information on the stroke Sb (second stroke) measured by the stroke sensor 14 and the distance Hb (second distance) measured by the distance sensor 13 at the second time point (current time point).

[0032] In S14, the control unit 11 calculates the radius Rb of the tire mounted at the second time point (current time point) based on the tire radius Ra, stroke Sa, distance Ha, stroke Sb, and distance Hb. Specifically, the control unit 11 calculates the tire radius Rb by substituting the tire radius Ra, stroke Sa, distance Ha, stroke Sb, and distance Hb into the above-mentioned equation (1).

[0033] In S15, the control unit 11 determines whether the calculated value of the tire radius Rb is different from the value of the tire radius Ra acquired in S12, and if they are different, the process proceeds to S16.

[0034] In S16, the control unit 11 updates the calculated tire radius Rb as the radius of the mounted tire and stores it. Also, the control unit 11 updates (rewrites) the radius Rb, stroke Sb, and distance Hb of the mounted tire at the second point in time (current point in time) as the radius Ra, stroke Sa, and distance Ha of the mounted tire at the first point in time and stores them. When the process of S16 is completed, the process of the flowchart in Fig. 4 ends. If the process proceeds to No from S15, the tire has not been replaced with a tire of a different diameter, and the process of the flowchart in Fig. 4 ends without updating the tire radius.

[0035] In this way, by updating the radius of the installed tire, the control unit 11 can calculate the vehicle speed based on the updated radius of the tire 20 and the tire rotation speed, and can calculate the vehicle speed with high accuracy even if a tire with a different diameter is installed. Similarly, the control unit 11 calculates the vehicle's mileage based on the updated radius of the tire 20 and the tire rotation speed, thereby being able to calculate the mileage with high accuracy even when tires of different diameters are installed.

[0036] As described above, the tire diameter calculation system of this embodiment includes the distance sensor 13 that measures the distance between the road surface and the vehicle body by irradiating electromagnetic waves, the stroke sensor 14 that measures the stroke of the suspension 30, and the control unit 11 that calculates the diameter of the mounted tire based on the distance measured by the distance sensor 13 and the stroke measured by the stroke sensor 14. When calculating the diameter of the mounted tire, the control unit 11 reflects changes due to the loading condition using the stroke sensor 14, so that the tire diameter can be appropriately calculated by the distance sensor 13 regardless of the loading condition.

[0037] In the tire diameter calculation system of this embodiment, the control unit 11 acquires information on a first distance between the road surface and the vehicle body and information on a first stroke of the suspension 30 at a predetermined time, acquires information on a second distance measured by the distance sensor 13 and information on the second stroke measured by the stroke sensor 14 at a time different from the predetermined time, and calculates the diameter of the mounted tire by subtracting the first distance and the second stroke from the sum of the second distance and the first stroke. By subtracting changes in the loading condition as the difference in the stroke sensor, the tire diameter can be calculated appropriately regardless of the loading condition.

[0038] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and modifications and the like are possible within the scope of the present invention. In the above-described embodiment, the tire radius Ra obtained in S12 of the flowchart in Fig. 4 is a value stored in advance in the control unit 11 or a value calculated in S14 immediately after the tire is replaced with a tire of a different diameter. However, this is not limited to this. For example, the tire radius Ra may be a value manually input by a mechanic to the control unit 11 when the tire is replaced.

[0039] In the above-described embodiment, the tire diameter is calculated by using the value measured by the stroke sensor 14 as is, but this is not limited to this. Generally, the suspension 30 is disposed at an angle relative to the vertical direction when viewed from the front or side of the vehicle 1. Therefore, the value measured by the stroke sensor 14 may be converted to a value in the vertical direction according to the angle of inclination of the suspension 30 and then substituted into equation (1). On the other hand, by arranging the stroke sensor 14 not parallel to the suspension 30 but vertically, the value measured by the stroke sensor 14 may be used as is. [Explanation of symbols]

[0040] 1: Vehicle (tire diameter calculation system) 10: Vehicle body 11: Control unit 12: Sensor unit 13: Distance sensor 14: Stroke sensor 15: Wheel speed sensor 16: Acceleration sensor 20: Tire 30: Suspension 31: Coil spring

Claims

1. a distance sensor that measures the distance between a road surface and a vehicle body by irradiating electromagnetic waves; a stroke sensor that measures the stroke of the suspension; a control unit that calculates the diameter of a mounted tire based on the distance measured by the distance sensor and the stroke measured by the stroke sensor.

2. The control unit acquiring information on a first distance between a road surface and a vehicle body and information on a first stroke of the suspension at a predetermined time point; acquiring information on a second distance measured by the distance sensor and information on a second stroke measured by the stroke sensor at a time point different from the predetermined time point; 2. The tire diameter calculation system according to claim 1, wherein the diameter of the mounted tire is calculated by subtracting the first distance and the second stroke from the sum of the second distance and the first stroke.

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