Tire friction characteristic measuring method and friction characteristic measuring device

Abstract

To provide a friction characteristic measurement method and a friction characteristic measurement device for a tire that enable a measurement in a state closer to an actual driving condition while controlling a cost and man-hour required for the measurement.SOLUTION: A friction characteristic measurement device 1 for a tire is a device for a four-wheel drive vehicle. A rear wheel 20 is equipped with the tire that is larger in diameter than a front wheel 15. The device 1 measures the tire mounted on the rear 20 wheel. A coupling 17 is interposed in a propeller shaft 16. A magnitude of fastening force of the coupling 17 is set to an arbitrary value based on a command from a fastening force setting section 28. The device 1 is equipped with body speed measurement sections 21-23, wheel angular velocity measurement sections 24, 25, shaft torque measurement sections 26, 27, and a controller 29. The controller 29 generates data pertaining to a friction characteristic of the tire mounted on the rear wheel 20 from a shaft torque and rotational peripheral speed of the rear wheel 20 and the magnitude of the fastening force of the coupling 17.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method and an apparatus for measuring frictional characteristics of a tire. [Background technology]

[0002] The development of vehicle behavior control technology requires measuring the friction characteristics of tires, which are evaluated based on the relationship between the slip ratio and the frictional force generated by the tires.

[0003] Conventional methods for measuring the frictional characteristics of tires include a method in which a measuring device equipped with a tire to be measured is towed by a trailer, and a method in which measurements are made using a bench test in a laboratory.

[0004] However, the above-mentioned measurement method differs from the actual driving condition. Therefore, improvements are required from the viewpoint of accurately measuring the friction characteristics of tires. Patent Document 1 proposes a method of measuring the friction state of a tire by mounting a tire with a built-in power generator on a vehicle and running the vehicle. If the method disclosed in Patent Document 1 is used, it is possible to mount a tire on an actual vehicle and measure the friction state, so it is thought that it is possible to measure under conditions closer to the actual driving condition. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2020-200012 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, the measurement method disclosed in Patent Document 1 uses tires prepared for measurement with internal power generators and sensor modules, which are different from tires that are actually mounted on vehicles. For this reason, it is difficult to apply the results of measurements made using the method disclosed in Patent Document 1 to actual vehicles. In addition, the measurement method disclosed in Patent Document 1 requires the preparation of measurement tires incorporating power generators and sensor modules for each type of tire to be measured, which increases the cost and labor required for measurement.

[0007] The present invention has been made to solve the above-mentioned problems, and has an object to provide a tire friction characteristic measuring method and device that are capable of measuring under conditions that are closer to actual driving conditions while reducing the cost and labor required for measurement. [Means for solving the problem]

[0008] A method for measuring tire friction characteristics according to one aspect of the present invention is a method for measuring friction characteristics defined by the relationship between a tire's slip ratio and frictional force. The method for measuring tire friction characteristics according to this aspect uses a running body having front and rear wheels, a driving force transmission path, and a coupling. The front and rear wheels are fitted with tires having different outer diameters. The driving force transmission path is a path formed so that running driving force is transmitted to both the front and rear wheels. The coupling is interposed in the driving force transmission path, and varies the torque distribution to each of the front and rear wheels depending on the magnitude of the fastening force.

[0009] The tire friction characteristic measuring method according to this aspect includes a measuring step, a slip ratio calculating step, a friction force calculating step, and a characteristic data generating step. In the measuring step, an axle torque for driving a target wheel to be measured out of the front wheels and the rear wheels, a traveling speed of the traveling body, and a rotational circumferential speed of the target wheel are measured while changing the magnitude of the fastening force of the coupling while the traveling body is traveling. In the slip ratio calculating step, a slip ratio is calculated from the traveling speed and the rotational circumferential speed for each magnitude of the fastening force. In the friction force calculating step, a friction force is calculated from the axle torque and an outer diameter of the target wheel for each magnitude of the fastening force. In the characteristic data generating step, data related to the friction characteristic is generated from the slip ratio and the friction force for each magnitude of the fastening force.

[0010] In the tire friction characteristic measuring method according to the above aspect, friction characteristics are measured using a running body equipped with tires having different outer diameters for the front and rear wheels. The running body can transmit driving force to both the front and rear wheels, and can vary torque distribution to the front and rear wheels by the fastening force of the coupling. In the measuring method according to the above aspect, data related to the tire friction characteristic of the target wheel that is the measurement target can be generated from the slip ratio calculated for each magnitude of fastening force and the friction force calculated for each magnitude of fastening force.

[0011] Therefore, the measurement method according to the above aspect allows measurement on an actual road, unlike bench tests in a laboratory (tests using a bench tester). In bench tests in a laboratory, the friction characteristics are measured by changing the load conditions on the tire, but the measurement method according to the above aspect allows measurement of the friction characteristics without changing the load conditions on the tire. As a result, the measurement method according to the above aspect allows measurement of the friction characteristics of a tire with high accuracy.

[0012] Moreover, in the measurement method according to the above aspect, it is not necessary to prepare a measurement tire incorporating a power generator or the like, as in the technology disclosed in the above Patent Document 1. Moreover, as the tire of the target wheel used in the measurement method according to the above aspect, a tire that is actually to be mounted on a traveling body can be used, so that it is possible to measure friction characteristics with higher accuracy.

[0013] In the tire friction characteristic measuring method according to the above aspect, the rear wheel may be fitted with a tire having an outer diameter larger than that of the front wheel, and the measuring step may be performed with the rear wheel as the target wheel.

[0014] In the tire friction characteristic measuring method according to the above aspect, the friction characteristic is measured using a rear wheel having a tire with a larger outer diameter than the front wheel as the target wheel. Since the rear wheel having a tire with a larger diameter than the front wheel is used as the target wheel in the measuring method according to the above aspect, the measurement can be performed with a driving force applied to the target wheel (rear wheel).

[0015] In the conventional measurement method in which a measurement device equipped with a tire is towed by a trailer, it is not possible to measure the friction characteristics with a driving force applied to the target wheel. In contrast, in the measurement method according to the above aspect, it is possible to measure the friction characteristics of a tire attached to a rear wheel with a driving force applied to the rear wheel, and therefore it is possible to perform measurements under actual driving conditions.

[0016] In the tire friction characteristic measuring method according to the above aspect, the rear wheel may be fitted with a tire having an outer diameter smaller than that of the front wheel, and the measuring step may be performed with the rear wheel as the target wheel.

[0017] In the tire friction characteristic measuring method according to the above aspect, the rear wheel, which is fitted with a tire with a smaller outer diameter than the front wheel, is used as the target wheel to measure the friction characteristics. Since the rear wheel, which is fitted with a tire with a smaller diameter than the front wheel, is used as the target wheel in the measuring method according to the above aspect, the measurement can be performed with a braking force applied to the target wheel (rear wheel). Therefore, the measuring method according to the above aspect can easily measure the tire friction characteristic during braking.

[0018] In the tire friction characteristic measuring method according to the above aspect, the measuring step may be performed in a state in which the traveling speed is substantially constant.

[0019] In the tire friction characteristic measuring method according to the above aspect, the measurement is performed while maintaining the traveling speed at a substantially constant value. By maintaining the traveling speed at a substantially constant value in this manner, it is possible to reduce measurement errors.

[0020] A tire friction characteristic measuring device according to one aspect of the present invention is a device for measuring friction characteristics defined by the relationship between a tire's slip ratio and frictional force. The tire friction characteristic measuring device according to this aspect includes a running body, an axle torque measuring unit, a running speed measuring unit, a wheel angular velocity measuring unit, and a controller. The running body has front and rear wheels, a drive force transmission path, and a coupling.

[0021] The front wheels and the rear wheels are fitted with tires having different outer diameters. The drive force transmission path is a path formed so that a driving force for running is transmitted to both the front wheels and the rear wheels. The coupling is interposed in the drive force transmission path and varies the torque distribution to each of the front wheels and the rear wheels depending on the magnitude of the fastening force.

[0022] The axle torque measuring unit measures an axle torque for driving a target wheel to be measured, one of the front wheels and the rear wheels, while changing the magnitude of the fastening force of the coupling while the running body is running. The running speed measuring unit measures the running speed of the running body while running. The wheel angular velocity measuring unit measures the angular velocity of the target wheel when the running body is running. The controller generates data related to the friction characteristics of the tire of the target wheel for each magnitude of the fastening force.

[0023] The controller has a wheel peripheral speed calculation unit, a slip ratio calculation unit, a friction force calculation unit, and a characteristic data generation unit. The wheel peripheral speed calculation unit calculates the rotational peripheral speed of the target wheel based on the angular velocity. The slip ratio calculation unit calculates a slip ratio from the traveling speed and the rotational peripheral speed for each magnitude of the fastening force. The friction force calculation unit calculates a friction force from the axle torque and an outer diameter of the target wheel for each magnitude of the fastening force. The characteristic data generation unit generates data related to the friction characteristic from the slip ratio and the friction force for each magnitude of the fastening force.

[0024] In the tire friction characteristic measuring device according to the above aspect, friction characteristics are measured using a running body equipped with tires having different outer diameters for the front and rear wheels. The running body can transmit driving force to both the front and rear wheels, and can vary the torque dissipation ratio by the fastening force of the coupling. In the measuring device according to the above aspect, the slip ratio calculation unit calculates the slip ratio for each magnitude of fastening force, and the friction force calculation unit calculates the friction force for each magnitude of fastening force. In the measuring device according to the above aspect, the characteristic data generation unit can generate data related to the friction characteristics of the tire of the target wheel that is the measurement target from the slip ratio and friction force associated with each fastening force.

[0025] Therefore, unlike bench tests in a laboratory (tests using a bench tester), the measurement device according to the above embodiment is capable of measuring friction characteristics by running on an actual road. In bench tests in a laboratory, the load conditions on the tire are changed to measure the friction characteristics, but the measurement device according to the above embodiment is capable of measuring friction characteristics without changing the load conditions on the tire. As a result, the measurement device according to the above embodiment can measure the friction characteristics of a tire with high accuracy.

[0026] Furthermore, in the measurement device according to the above aspect, it is not necessary to prepare a measurement tire incorporating a power generator or the like, as in the technology disclosed in the above Patent Document 1. In addition, as the tire of the target wheel in the measurement device according to the above aspect, a tire to be actually mounted on a traveling body can be used, so that it is possible to measure friction characteristics with higher accuracy.

[0027] A tire friction characteristic measuring device according to another aspect of the present invention is a device that is attached to a running body and measures friction characteristics defined by the relationship between a tire's slip ratio and frictional force. The running body has front and rear wheels, a driving force transmission path, and a coupling. The front and rear wheels are fitted with tires having different outer diameters. The driving force transmission path is a path formed so that running driving force is transmitted to both the front and rear wheels. The coupling is interposed in the driving force transmission path and varies the torque distribution to each of the front and rear wheels depending on the magnitude of the fastening force.

[0028] The tire friction characteristic measuring device according to this aspect includes an axle torque measuring unit, a traveling speed measuring unit, a wheel angular velocity measuring unit, and a controller. The axle torque measuring unit measures an axle torque for driving a target wheel to be measured, one of the front wheels and the rear wheels, while changing the magnitude of the fastening force of the coupling while the traveling body is traveling. The traveling speed measuring unit measures the traveling speed of the traveling body while traveling. The wheel angular velocity measuring unit measures the angular velocity of the target wheel when the traveling body is traveling. The controller generates data related to the friction characteristic of the tire on the target wheel for each magnitude of the fastening force.

[0029] The controller includes a wheel peripheral speed calculation unit, a slip ratio calculation unit, a friction force calculation unit, and a characteristic data generation unit.

[0030] The wheel peripheral speed calculation unit calculates the rotational peripheral speed of the target wheel based on the angular velocity. The slip ratio calculation unit calculates a slip ratio from the traveling speed and the rotational peripheral speed for each magnitude of the fastening force. The friction force calculation unit calculates a friction force from the axle torque and an outer diameter of the target wheel for each magnitude of the fastening force. The characteristic data generation unit generates data related to the friction characteristic from the slip ratio and the friction force for each magnitude of the fastening force.

[0031] In the tire friction characteristic measuring device according to the above aspect, friction characteristics are measured using a running body on which tires with different outer diameters are mounted for the front and rear wheels. The running body is configured to be able to transmit driving force to both the front and rear wheels and to vary the fastening force of the coupling. In the measuring device according to the above aspect, the slip ratio calculation unit calculates a slip ratio for each magnitude of fastening force, and the friction force calculation unit calculates a friction force for each magnitude of fastening force. In the measuring device according to the above aspect, the characteristic data generation unit can generate data related to the friction characteristics of the tire of the target wheel that is the measurement target from the slip ratio and friction force associated with each fastening force.

[0032] Therefore, unlike bench tests in a laboratory (tests using a bench tester), the measurement device according to the above embodiment is capable of measuring friction characteristics by running on an actual road. In bench tests in a laboratory, the load conditions on the tire are changed to measure the friction characteristics, but the measurement device according to the above embodiment is capable of measuring friction characteristics without changing the load conditions on the tire. As a result, the measurement device according to the above embodiment can measure the friction characteristics of a tire with high accuracy.

[0033] Furthermore, in the measurement device according to the above aspect, it is not necessary to prepare a measurement tire incorporating a power generator or the like, as in the technology disclosed in the above Patent Document 1. In addition, as the tire of the target wheel in the measurement device according to the above aspect, a tire to be actually mounted on a traveling body can be used, so that it is possible to measure friction characteristics with higher accuracy.

[0034] Furthermore, the measurement device according to the above aspect does not include a running body as a part of the device, but includes a configuration in which the axle torque measurement unit, the running speed measurement unit, the wheel angular velocity measurement unit, and the controller are "post-attached" to the running body. Therefore, the measurement device according to the above aspect can measure friction characteristics using a running body on which the target tire is actually to be mounted. Also, since the measurement device does not include a running body as a part of the measurement device, it is possible to suppress an increase in the cost of the device.

[0035] In the tire friction characteristic measuring device relating to the above-mentioned aspect, the rear wheel may be fitted with a tire having an outer diameter larger than that of the front wheel, and the controller may perform measurement of the friction characteristics using the rear wheel as the target wheel.

[0036] In the tire friction characteristic measuring device according to the above aspect, the friction characteristic is measured using a rear wheel having a tire with a larger outer diameter than the front wheels as the target wheel. In the measurement method according to the above aspect, the rear wheel having a tire with a larger diameter than the front wheels is used as the target wheel, so that the measurement can be performed with a driving force applied to the target wheel (rear wheel).

[0037] In the conventional measuring device, which measures by towing a tire-mounted measuring device with a trailer, it was not possible to measure the friction characteristics with a driving force applied to the target wheel. In contrast, the measuring device according to the above aspect can measure the friction characteristics of a tire mounted on a rear wheel with a driving force applied to the rear wheel, making it possible to measure under actual driving conditions.

[0038] In the tire friction characteristic measuring device relating to the above-mentioned aspect, the rear wheel may be fitted with a tire having an outer diameter smaller than that of the front wheel, and the controller may perform measurement of the friction characteristics using the rear wheel as the target wheel.

[0039] In the tire friction characteristic measuring device according to the above aspect, the friction characteristic can be measured by using the rear wheel, which is fitted with a tire with a smaller outer diameter than the front wheel, as the target wheel. In addition, in the measuring device according to the above aspect, the rear wheel, which is fitted with a tire with a smaller diameter than the front wheel, is used as the target wheel, so that the measurement can be performed with a braking force applied to the target wheel (rear wheel). Therefore, the measuring device according to the above aspect can easily measure the friction characteristic of the tire during braking.

[0040] In the tire friction characteristic measuring device according to the above aspect, the controller may measure the friction characteristic while the traveling speed is substantially constant.

[0041] In the tire friction characteristic measuring device according to the above aspect, the measurement can be performed while maintaining the traveling speed substantially constant. By maintaining the traveling speed substantially constant in this manner, it is possible to reduce measurement errors. Effect of the Invention

[0042] In each of the above aspects, it is possible to perform measurements under conditions that are closer to actual driving conditions while suppressing the cost and man-hours required for measurements. [Brief description of the drawings]

[0043] [Figure 1] 1 is a schematic diagram showing a schematic configuration of a tire friction characteristic measuring device according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a block diagram showing a control configuration of the friction characteristic measuring device. [Diagram 3] 10 is a flowchart showing a friction characteristic data generating method executed by a controller. [Figure 4] 4 is a graph showing an example of a fastening force set by a fastening force setting unit. [Diagram 5] FIG. 2 is a schematic diagram showing the measurement principle of friction characteristics by a friction characteristic measuring device. [Figure 6] 4 is a graph showing an example of friction characteristic data measured by a friction characteristic measuring device. [Figure 7] FIG. 4 is a schematic diagram showing a schematic configuration of a tire friction characteristic measuring device according to a second embodiment of the present invention. [Figure 8] 11 is a part of a flowchart showing a frictional characteristic measuring method according to Modification 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the embodiment described below is an example of the present invention, and the present invention is not limited to the following embodiment except for the essential configuration.

[0045] In the figures used in the following description, "Fr" indicates the front (traveling direction) in the vehicle's fore-and-aft direction, "Re" indicates the rear in the vehicle's fore-and-aft direction, "Le" indicates the left in the vehicle's width direction, and "Ri" indicates the right in the vehicle's width direction.

[0046] [First embodiment] 1. Overview of tire friction characteristic measuring device 1 The schematic configuration of a tire friction characteristic measuring device 1 according to a first embodiment of the present invention will be described with reference to FIG.

[0047] The tire friction characteristic measuring device (hereinafter, may be simply referred to as "measuring device") 1 according to this embodiment is configured using a four-wheel drive vehicle, which is an example of a traveling object. As shown in Fig. 1, the four-wheel drive vehicle used in the measuring device 1 includes front wheels 15 and rear wheels 20, a prime mover 11 that generates driving force for traveling, a transmission 12, a power split device (PTO: Power Take-Off) 13, a propeller shaft 16, an electronically controlled coupling 17, a differential gear 18, and drive shafts 14, 19.

[0048] In this embodiment, the outer diameter Dr of the tire mounted on the rear wheel 20 is set to be larger than the outer diameter Df of the tire mounted on the front wheel 15. The object for which the measuring device 1 according to this embodiment is to measure friction characteristics is the rear wheel 20. That is, the object wheel of the measuring device 1 according to this embodiment is the rear wheel 20.

[0049] The prime mover 11 is an electric motor or an engine, and generates driving force for running the four-wheel drive vehicle.

[0050] The PTO 13 is a device that splits the driving force transmitted from the prime mover 11 via the transmission 12 between the drive shaft 14 and the propeller shaft 16. In a four-wheel drive vehicle, the PTO 13 is provided in the driving force transmission path from the transmission 12 to the front wheels 15 and the rear wheels 20, so that the driving force generated by the prime mover 11 is transmitted to both the front wheels 15 and the rear wheels 20.

[0051] The electronically controlled coupling 17 is provided between the propeller shaft 16 and the differential gear 18 in the drive force transmission path. The electronically controlled coupling 17 is a device that sets the magnitude of the fastening force to an arbitrary value based on a command from a fastening force setting unit 28, which will be described later. In a four-wheel drive vehicle, the torque distribution to the front wheels 15 and the rear wheels 20 is set by the magnitude of the fastening force in the electronically controlled coupling 17.

[0052] 1, the measurement device 1 according to this embodiment further includes three vehicle body speed measuring units 21-23, two wheel angular velocity measuring units 24, 25, the above-mentioned fastening force setting unit 28, and a controller 29. The vehicle body speed measuring units 21-23, the wheel angular velocity measuring units 24, 25, the axle torque measuring units 26, 27, and the fastening force setting unit 28 are signal-connected to the controller 29. Note that one vehicle body speed measuring unit, one wheel angular velocity measuring unit, and one axle torque measuring unit may be provided.

[0053] The vehicle speed measuring unit 21 is a speedometer using a global positioning system (GPS) and is a device for detecting the moving speed of the vehicle. The vehicle speed measuring units 22 and 23 are laser light Doppler type speedometers and are also devices for detecting the moving speed of the vehicle. In this embodiment, the vehicle speed measuring units 22 and 23 are disposed near the position where the rear wheel 20 is disposed.

[0054] The wheel angular velocity measuring units 24, 25 can be realized by, for example, a device that measures pulses with an electromagnetic pickup using a pulser ring and converts the pulses into rotation. The wheel angular velocity measuring units 24, 25 are provided so as to be able to detect the angular velocities of the left and right rear wheels 20, respectively.

[0055] 2. Control configuration of measurement device 1 The control configuration of the measurement device 1 will be described with reference to FIG.

[0056] 2, vehicle body speed measuring units 21-23, wheel angular velocity measuring units 24, 25, axle torque measuring units 26, 27, and a clamping force setting unit 28 are signal-connected to a controller 29. The clamping force setting unit 28 is signal-connected to the electronically controlled coupling 17.

[0057] The controller 29 is configured to have a microprocessor including an MPU / CPU, ASIC, ROM, RAM, etc., and a memory. The controller 29 issues a command to the clamping force setting unit 28 to control the magnitude of the clamping force by executing firmware and the like previously stored in the memory, and generates data related to the friction characteristics of the tire mounted on the rear wheel 20 for each magnitude of the clamping force based on various input information.

[0058] The controller 29 has a wheel peripheral speed calculation unit 291, a slip ratio calculation unit 292, a friction force calculation unit 293, a data storage unit 294, and a characteristic data generation unit 295. The wheel peripheral speed calculation unit 291 calculates the rotational peripheral speed Vw of the rear wheel 20 based on the angular speed ω (rad / sec.) measured by the wheel angular speed measurement units 24, 25. Specifically, the rotational peripheral speed Vw is calculated using the following relational expression. Vw = (Dr / 2) × ω (Equation 1) The slip ratio calculation unit 292 calculates the slip ratio Sr based on the vehicle speed Vv measured by the vehicle speed measurement units 21-23 and the rotational circumferential speed Vw of the rear wheels 20 calculated by the above-mentioned relational expression 1. Specifically, the slip ratio Sr is calculated using the following relational expression. Sr = (Vw - Vv) / Vw (Equation 2)

[0059] The friction force calculation unit 293 calculates the friction force Ff based on the shaft torque Ts measured by the shaft torque measurement units 26, 27 and the outer diameter Dr of the rear wheel 20. Specifically, the friction force Ff is calculated using the following relational expression. Ff = Ts / Dr (Equation 3) The data storage unit 294 stores the calculated slip ratio Sr and the friction force Ff in association with each other for each magnitude of the fastening force of the electronically controlled coupling 17 set by the fastening force setting unit 28. The characteristic data generation unit 295 generates friction characteristic data of the tire of the rear wheel 20 by using the data stored in the data storage unit 294.

[0060] 3. Method of generating friction characteristic data executed by controller 29 A method for generating friction characteristic data executed by the controller 29 will be described with reference to Fig. 3 and Fig. 4. Fig. 4 is a graph showing an example of the fastening force of the electronically controlled coupling 17 set by the fastening force setting unit 28.

[0061] The controller 29 acquires information on the vehicle speed Vv from the vehicle speed measuring units 21 to 23, the angular velocity ω of the rear wheels 20 from the wheel angular velocity measuring units 24, 25, and the axle torque Ts of the rear wheels 20 from the axle torque measuring units 26, 27 (step S1). Note that the acquisition of each piece of information by the controller 29 is performed at any time during control.

[0062] Next, the controller 29 monitors the vehicle speed Vv over time and determines whether the vehicle is in a constant speed traveling state (step S2). The controller 29 continues monitoring until the vehicle is in a constant speed traveling state (step S2: NO). Note that the constant speed traveling state of the vehicle is sufficient if the vehicle traveling speed Vv is approximately constant (for example, within a range of ±3 km / h, preferably within a range of ±1 km / h).

[0063] When the controller 29 determines that the vehicle is in a constant speed traveling state (step S2: YES), it issues a command to the fastening force setting unit 28 to set the fastening force F of the electronically controlled coupling 17 to F1 (step S3). Then, the controller 29 calculates the slip ratio Sr in the slip ratio calculation unit 292 (step S4), and calculates the friction force Ff in the friction force calculation unit 293 (step S5). The methods of calculating the slip ratio Sr and the friction force Ff are as described above.

[0064] Next, the controller 29 associates the slip ratio Sr and the friction force Ff calculated for each magnitude of the fastening force F and temporarily stores them in the data storage unit 294 (step S6). Then, the controller 29 determines whether the fastening force F is equal to or greater than a preset upper limit value F2 (step S7). If the controller 29 determines that the fastening force F is less than F2 (step S7: NO), it issues a command to the fastening force setting unit 28 to slightly increase the fastening force F (step S8), and repeats the execution of steps S4 to S8.

[0065] Here, the relationship between the elapsed time in the execution of steps S3 to S8 and the fastening force F is, for example, as shown in Fig. 4. As shown in Fig. 4, the fastening force F is set to F1 at elapsed time T1 (step S3), and is gradually increased so that the fastening force F reaches an upper limit value F2 at elapsed time T2.

[0066] Returning to Fig. 3, when the controller 29 determines that the fastening force F is equal to or greater than the upper limit value F2 (step S7: YES), it reads out a plurality of data stored in the data storage unit 294 and generates data related to the frictional characteristics of the tire of the rear wheel 20 (step S9). After that, the controller 29 issues a command to the fastening force setting unit 28 to reduce the fastening force F from the upper limit value F2 to the lower limit value F1 (step S10). As shown in Fig. 4, upon receiving the command, the fastening force setting unit 28 gradually reduces the fastening force F from the upper limit value F2 to the lower limit value F1 from the elapsed time T3 to the elapsed time T4.

[0067] In this embodiment, when the clamping force F is gradually decreased from the upper limit value F2 to the lower limit value F1, the slip ratio Sr and the friction force Ff for each magnitude of the clamping force F are not calculated, but they may be calculated separately in order to increase the number of data.

[0068] 4. Principle of measurement of data related to friction characteristics using the measuring device 1 The principle of measurement of data relating to friction characteristics by the measurement device 1 will be described with reference to FIG.

[0069] 5, the measurement device 1 according to this embodiment uses a four-wheel drive vehicle, and the measurement target (target wheel) is a rear wheel 20 fitted with a tire with a larger diameter than the front wheels 15. For this reason, shaft torque measuring units 26, 27 are provided on a drive shaft 19 connected to the rear wheel 20, which is the target wheel.

[0070] The fastening force F at the electronically controlled coupling 17 inserted in the driving force transmission path is changed under the control of the fastening force setting unit 28 (see FIG. 4). As a result, the measurement device 1 according to this embodiment can measure data related to the friction characteristics of the tire of the rear wheel 20 equipped with a large-diameter tire while a driving force is being applied to the rear wheel 20.

[0071] 5. Example of data on friction characteristics obtained An example of data relating to friction characteristics obtained by measurement using the measurement device 1 according to this embodiment will be described with reference to FIG.

[0072] 6, in an example of data relating to friction characteristics, with slip ratio Sr on the horizontal axis and friction force Ff on the vertical axis, as the slip ratio increases from Sr1 to Sr2, the friction force Ff also increases from Ff1 to Ff2. Then, as the slip ratio Sr exceeds Sr2 and increases from Sr3 to Sr4, the friction force Ff decreases from Ff3 to Ff4.

[0073] The data shown in FIG. 6 is merely an example, and will vary depending on the tire tread compound, tread pattern, and internal structure (for example, the number of belts and the wire angle of the belt).

[0074] 6.Effects In the tire friction characteristic measuring device 1 and the measuring method using the measuring device 1 according to the present embodiment, friction characteristics are measured using a four-wheel drive vehicle equipped with rear wheels 20 on which tires having an outer diameter larger than that of the front wheels 15 are mounted. The four-wheel drive vehicle is configured to transmit driving force to both the front wheels 15 and the rear wheels 20, and to vary the fastening force F of the electronically controlled coupling 17 by the fastening force setting unit 28. In the measuring device 1, the slip ratio calculation unit 292 of the controller 29 calculates the slip ratio Sr for each magnitude of the fastening force F, and the friction force calculation unit 293 calculates the tire friction force Ff for each magnitude of the fastening force F. In the measuring device 1, the characteristic data generation unit 295 can generate data related to the friction characteristics of the tire of the rear wheel 20 to be measured from the slip ratio Sr and the friction force Ff associated with each fastening force F.

[0075] Therefore, unlike laboratory bench tests (tests using bench testing machines), the measurement device 1 is capable of measuring friction characteristics by driving on an actual road. In laboratory bench tests, the load conditions on the tire are changed to measure the friction characteristics, but the measurement device 1 according to this embodiment is capable of measuring the friction characteristics without changing the load conditions on the tire. As a result, the measurement device 1 can measure the friction characteristics of a tire with high accuracy.

[0076] Furthermore, with the measurement device 1 according to this embodiment, there is no need to prepare a measurement tire incorporating a power generator or the like, as in the technique disclosed in the above-mentioned Patent Document 1. In addition, since a tire that is the subject of actual performance development can be used as the tire of the rear wheel 20 in the measurement device 1, it is possible to measure friction characteristics with higher accuracy.

[0077] Furthermore, in the measurement device 1 according to this embodiment, the controller 29 measures the friction characteristics when the vehicle is traveling at a constant speed. Therefore, in the measurement device 1 according to this embodiment, the measurement is performed while the traveling speed is kept substantially constant, thereby making it possible to reduce measurement errors.

[0078] As described above, the measuring device 1 according to the present embodiment and the measuring method using the measuring device 1 make it possible to perform measurements under conditions that are closer to actual driving conditions while suppressing the cost and man-hours required for measurement.

[0079] [Second embodiment] The configuration of a tire friction characteristic measuring device 2 according to a second embodiment of the present invention will be described with reference to Fig. 7. In the following description, only differences from the first embodiment will be described.

[0080] As shown in FIG. 7, the frictional characteristic measuring device (hereinafter, may be simply referred to as "measuring device") 2 according to this embodiment can also measure the frictional characteristics of tires using a four-wheel drive vehicle. In a four-wheel drive vehicle used with the measuring device 2 according to this embodiment, the outer diameter Dr2 of the tire of the rear wheel 40, which is the object of measuring the frictional characteristics of the tire, is set to be smaller than the outer diameter Df2 of the tire of the front wheel 35. Axle torque measuring units 26, 27 are attached to a drive shaft 19 connected to the rear wheel 40. An electronically controlled coupling 17 similar to that of the first embodiment is inserted in a driving force transmission path, which is a path for transmitting the driving force generated by the prime mover 11.

[0081] In the measuring device 2 according to this embodiment, the four-wheel drive vehicle is also placed in a constant speed traveling state, and the fastening force F at the electronically controlled coupling 17 interposed in the driving force transmission path is changed under the control of the fastening force setting unit 28. As a result, the measuring device 2 according to this embodiment can measure data relating to the friction characteristics of the rear wheel 40 fitted with a small-diameter tire while a braking force is being applied to the rear wheel 40.

[0082] In the measuring device 2 of this embodiment, the rear wheel 40, which is fitted with a tire with a smaller diameter than the front wheel 35, is used as the target wheel, and data related to friction characteristics is measured while a braking force is applied to the rear wheel 40, and the same effects as in the first embodiment can be obtained.

[0083] In this case, the slip ratio Sr is calculated using the following formula. Sr = (Vv - Vw) / Vv (Equation 4) [Variations] A method for measuring tire friction characteristics according to a modified example will be described with reference to Fig. 8. Note that since this modified example employs an apparatus configuration common to the first embodiment or the second embodiment, a description of the apparatus configuration will be omitted.

[0084] In the measurement method according to the first embodiment, when it is determined that the fastening force F is equal to or greater than the upper limit value F2 (step S7: YES), data relating to the frictional characteristics is generated (step S9) and a command is issued to the fastening force setting unit 28 to reduce the fastening force F from the upper limit value F2 to the lower limit value F1 (step S10). In contrast, in the measurement method according to this modification, after the fastening force F reaches the upper limit value F2, the measurement of the frictional force Ff is continued while the fastening force F is reduced from the upper limit value F2 to the lower limit value F1 from the elapsed time T3 to T4 (see FIG. 4).

[0085] Specifically, as shown in FIG. 8, after the fastening force F reaches an upper limit value F2, the controller 29 gradually reduces the fastening force F of the electronically controlled coupling 17 to F1 (step S11), and calculates the slip ratio Sr (step S12) and the friction force Ff (step S13) in the same manner as described above.

[0086] Next, the controller 29 associates the slip ratio Sr and the friction force Ff calculated for each magnitude of the clamping force F and temporarily stores them in the data storage unit 294 (step S14). The controller 29 executes steps S11 to S15 until the clamping force F reaches the lower limit value F1 (step S15: NO). When the controller 29 determines that the clamping force F has reached F1 (step S15), it reads out a plurality of data stored in the data storage unit 294 and generates data related to the friction characteristics of the tire of the rear wheel 20 (step S16).

[0087] The measurement method according to this modification can provide the same effects as those of the first or second embodiment. Moreover, in the measurement method according to this modification, measurement is performed even when the fastening force F of the electronically controlled coupling 17 decreases from the upper limit value F2 to the lower limit value F1, so that the number of measurement data can be increased and high measurement accuracy can be achieved.

[0088] [Other variations] In the first embodiment, the second embodiment, and the modified example, the friction characteristic measuring device 1, 2 including a four-wheel drive vehicle is adopted, but the present invention is not limited thereto. That is, as shown in FIG. 2, the vehicle body speed measuring units 21-23, the wheel angular velocity measuring units 24, 25, the axle torque measuring units 26, 27, the fastening force setting unit 28, and the controller 29 can be unitized into a measuring device main unit 30. Then, by mounting the measuring device main unit 30 on a general-purpose four-wheel drive vehicle and providing a difference in the tire outer diameter between the front and rear wheels, it is possible to perform measurements in the same manner as in the first embodiment, the second embodiment, or the modified example. In this case, the measuring device main unit 30 corresponds to the "tire friction characteristic measuring device".

[0089] In the first and second embodiments, the measurement is started after the vehicle speed becomes constant, but the present invention is not limited to this. For example, the fastening force F of the electronically controlled coupling 17 may be set to a predetermined value, and the measurement value may be obtained when the vehicle speed falls within a predetermined range.

[0090] In the first and second embodiments and the modified example, data associating the slip ratio Sr with the frictional force Ff is temporarily stored in the data storage unit 294, but the present invention is not limited to this. For example, friction characteristic data may be generated directly using data associating the slip ratio Sr with the frictional force Ff.

[0091] In the above embodiment, each step is described as being automatically executed by the controller 29, but in the present invention, each step may be executed by an operation of an operator.

[0092] In addition, in the above embodiment, either the front wheels 15, 35 or the rear wheels 20, 40 were the measurement targets, but by attaching a wheel angular velocity measuring unit and an axle torque measuring unit to each of them, it is also possible to measure the friction characteristics of both the front wheels and the rear wheels simultaneously. [Explanation of symbols]

[0093] 1,2 Friction characteristic measuring device 15,35 Front wheel 17 Electronically controlled coupling 20,40 rear wheel 21~23 Vehicle speed measurement section 24,25 Wheel angular velocity measurement unit 26,27 Shaft torque measurement section 28 Fastening force setting section 29 Controller 30 Measurement device main unit 291 Wheel peripheral speed calculation section 292 Slip ratio calculation section 293 Friction force calculation section 295 Characteristics Data Generation Unit

Claims

1. A method for measuring a friction characteristic of a tire, the method comprising the steps of: measuring a friction characteristic defined by a relationship between a slip ratio and a frictional force of the tire; Front and rear wheels are fitted with tires having different outer diameters; a driving force transmission path formed so that a driving force is transmitted to both the front wheels and the rear wheels; a coupling that is inserted in the driving force transmission path and changes a torque distribution to each of the front wheels and the rear wheels depending on a magnitude of a fastening force; A vehicle having the following structure is used: a measuring step of measuring an axle torque for driving a target wheel to be measured out of the front wheels and the rear wheels, a traveling speed of the traveling body, and a rotational circumferential speed of the target wheel while changing a magnitude of the fastening force of the coupling during traveling of the traveling body; a slip ratio calculation step of calculating a slip ratio from the traveling speed and the rotational peripheral speed for each magnitude of the fastening force; a friction force calculation step of calculating a friction force from the axle torque and an outer diameter of the target wheel for each magnitude of the fastening force; a characteristic data generating step of generating data relating to the friction characteristic from the slip ratio and the friction force for each magnitude of the fastening force; Equipped with Method for measuring tire friction characteristics.

2. The method for measuring frictional characteristics of a tire according to claim 1, The rear wheels are fitted with tires having a larger outer diameter than the front wheels, The measurement step is performed by using the rear wheel as the target wheel. Method for measuring tire friction characteristics.

3. The method for measuring frictional characteristics of a tire according to claim 1, The rear wheels are fitted with tires having a smaller outer diameter than the front wheels, The measurement step is performed by using the rear wheel as the target wheel. Method for measuring tire friction characteristics.

4. The tire friction characteristic measuring method according to any one of claims 1 to 3, The measuring step is performed while the traveling speed is substantially constant. Method for measuring tire friction characteristics.

5. A tire friction characteristic measuring device that measures friction characteristics defined by a relationship between a slip ratio and a frictional force of a tire, comprising: Front and rear wheels are fitted with tires having different outer diameters; a driving force transmission path formed so that a driving force is transmitted to both the front wheels and the rear wheels; a coupling that is interposed in the driving force transmission path and changes a torque distribution to each of the front wheels and the rear wheels depending on a magnitude of a fastening force; A traveling body having the an axle torque measuring unit that measures an axle torque for driving a target wheel that is a measurement target among the front wheels and the rear wheels while changing a magnitude of the fastening force of the coupling during traveling of the traveling body; a running speed measurement unit that measures a running speed of the running object while the running object is running; a wheel angular velocity measuring unit that measures an angular velocity of the target wheel when the running object is running; a controller that generates data related to a friction characteristic of a tire of the target wheel for each magnitude of the fastening force; Equipped with The controller: a wheel circumferential speed calculation unit that calculates a rotational circumferential speed of the target wheel based on the angular velocity; a slip ratio calculation unit that calculates a slip ratio from the traveling speed and the rotational peripheral speed for each magnitude of the fastening force; a friction force calculation unit that calculates a friction force from the axle torque and an outer diameter of the target wheel for each magnitude of the fastening force; a characteristic data generating unit that generates data related to the friction characteristic from the slip ratio and the friction force for each magnitude of the fastening force; having A device for measuring tire friction characteristics.

6. Front and rear wheels are fitted with tires having different outer diameters; a driving force transmission path formed so that a driving force is transmitted to both the front wheels and the rear wheels; a coupling that is interposed in the driving force transmission path and changes a torque distribution to each of the front wheels and the rear wheels depending on a magnitude of a fastening force; The vehicle is attached to the vehicle body having the A tire friction characteristic measuring device that measures friction characteristics defined by a relationship between a slip ratio and a frictional force of a tire, comprising: an axle torque measuring unit that measures an axle torque for driving a target wheel that is a measurement target among the front wheels and the rear wheels while changing a magnitude of the fastening force of the coupling during traveling of the traveling body; a running speed measurement unit that measures a running speed of the running object while the running object is running; a wheel angular velocity measuring unit that measures an angular velocity of the target wheel when the running object is running; a controller that generates data related to a friction characteristic of a tire of the target wheel for each magnitude of the fastening force; Equipped with The controller: a wheel circumferential speed calculation unit that calculates a rotational circumferential speed of the target wheel based on the angular velocity; a slip ratio calculation unit that calculates a slip ratio from the traveling speed and the rotational peripheral speed for each magnitude of the fastening force; a friction force calculation unit that calculates a friction force from the axle torque and an outer diameter of the target wheel for each magnitude of the fastening force; a characteristic data generating unit that generates data related to the friction characteristic from the slip ratio and the friction force for each magnitude of the fastening force; having A device for measuring tire friction characteristics.

7. The tire friction characteristic measuring device according to claim 5 or 6, The rear wheels are fitted with tires having a larger outer diameter than the front wheels, The controller measures the friction characteristics of the rear wheels as the target wheels. A device for measuring tire friction characteristics.

8. The tire friction characteristic measuring device according to claim 5 or 6, The rear wheels are fitted with tires having a smaller outer diameter than the front wheels, The controller measures the friction characteristics of the rear wheels as the target wheels. A device for measuring tire friction characteristics.

9. The tire friction characteristic measuring device according to any one of claims 5 to 8, The controller measures the friction characteristics while the traveling speed is substantially constant. A device for measuring tire friction characteristics.

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