JP7167543B2 - Method for evaluating tire braking performance on ice - Google Patents

Description

TECHNICAL FIELD The present invention relates to a tire braking performance evaluation method on ice for evaluating braking performance on a wet icy road surface.

Patent Literature 1 below proposes a method of evaluating the on-ice performance of a tire using a drum having an ice sheet-like icy surface formed on the inner peripheral surface thereof. In the above method, the braking performance of the tire on ice is evaluated based on the reaction force of the tire running on the icy road surface. In the above method, in order to maintain the condition of the icy road surface close to that of the ice test using an actual vehicle, the cooling gas injection means is used to blow away moisture on the icy road surface and maintain the icy road surface in a dry state.

However, in urban areas in cold regions, there are many conditions of wet icy road surfaces in which a thin water film (for example, a water film with a thickness of about 1.0 mm) is formed on the icy road surface. As a result of research by the present inventors, it has been found that, depending on the tire, the braking performance on ice on a dry icy road surface differs greatly from that on a wet icy road surface. FIG. 4 shows "μs characteristics" for dry and wet icy road surfaces obtained by conducting actual vehicle tests on three types of tires A, B, and C on the market. Table 1 shows the values of the maximum friction coefficient μmax of each tire A to C in FIG. In tire C, since the coefficient of friction does not peak on a wet and icy road surface, the value at a slip speed of 1.5 km/h is taken as the maximum coefficient of friction μmax.

As shown in Table 1,
(1) With Tire A, the maximum coefficient of friction μmax decreases from 100 to 94, 6 points from a dry ice road surface to a wet ice road surface.
(2) With tire B, the maximum coefficient of friction μmax decreases from 114 to 92, from a dry icy road surface to a wet icy road surface, by 22 points.
(3) With the tire C, the maximum coefficient of friction μmax decreases from 105 to 72, 33 pts, from the dry icy road surface to the wet icy road surface.

In this way, in the conventional evaluation method for dry icy road surfaces, the order of B > C > A was evaluated as excellent on ice performance, but on wet icy roads, the order was A > B > C. It can be evaluated as having excellent performance on ice.

Therefore, when evaluating the braking performance of a tire on ice, it is important to evaluate not only on a dry icy road surface but also on a wet icy road surface.

JP 2007-78667 A

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for evaluating braking performance on ice of a tire capable of evaluating braking performance on ice on a wet icy road surface.

The present invention is a method for evaluating braking performance on ice of a tire using an icy road frozen on the inner peripheral surface of the driving drum of an on-ice test apparatus having a cylindrical driving drum and installed indoors,
an ice road surface forming step of forming an ice road surface on the inner peripheral surface of the driving drum in a first room temperature state in which the room temperature is below freezing;
The interior of the room is set to a second room temperature higher than the first room temperature, and the ice road surface is a wet ice road surface having a water film formed on the surface thereof, and the wet ice road surface is set to the second room temperature and the wet surface. and a testing step of performing an ice braking test of the tire on an icy surface.

In the method for evaluating braking performance on ice of a tire according to the present invention, the second room temperature is preferably 5 to 10° C. higher than the first temperature.

In the method for evaluating tire braking performance on ice according to the present invention, the first room temperature is preferably in the range of -3 to -8°C.

In the method for evaluating braking performance on ice of a tire according to the present invention, it is preferable that the second room temperature is in the range of +1°C to +3°C.

In the method for evaluating braking performance on ice of a tire according to the present invention, the step of forming an icy road surface includes:
forming an ice floe on the inner peripheral surface;
a step of smoothing the surface of the formed ice floe by scraping it with a cutting blade;
polishing the smoothed surface of the ice floe with a polishing tire to make it a mirror finish.

In the method for evaluating braking performance on ice of a tire according to the present invention, the test step includes:
a rotational driving step of relatively rotating the drive drum and the test tire while the outer peripheral surface of the test tire is pressed against the wet ice road surface;
a measuring step of measuring a reaction force applied to the test tire from the wet ice road surface during the rotating step;
a spacing step of spacing the test tire from the wet ice road surface;
a lateral movement step of laterally moving the test tire away from the wet ice road surface in the axial direction of the drum;
a calculation step of calculating a coefficient of friction from the reaction force measured in the measurement step;
Moreover, the rotational driving step, the measuring step, the separating step, and the lateral moving step are sequentially repeated for a plurality of cycles,
It is preferable to evaluate braking performance on a wet ice road surface based on the coefficient of friction calculated in at least some of the cycles.

In the method for evaluating the braking performance of a tire on ice according to the present invention, in the lateral movement step, the distance of lateral movement of the test tire is preferably 5 to 20 mm.

In the method for evaluating braking performance on ice of a tire according to the present invention, in the rotation driving step, the vertical load acting on the test tire from the driving drum reaches a value specified as the test load for 2 seconds or more and 10 seconds or less. It is preferred to maintain the test load pressed during.

In the present invention, in the icy surface formation step, the interior of the room is kept at the first room temperature below the freezing point, so that the icy surface can be formed on the inner circumferential surface of the driving drum.

In the test process, the interior of the room is set to a second room temperature higher than the first room temperature, so that the surface of the icy road surface is melted to form a wet icy road surface with a film of water formed on the surface. At this time, the surface of the icy road surface is naturally and gradually melted by the second room temperature, so that the occurrence of cracks or the like on the icy road surface S can be prevented, and the surface of the icy road surface S is uniformly melted over the entire circumference. can be scratched.

When water is sprinkled on an icy surface to form a water film, cracks are likely to occur in the icy surface due to temperature differences. In addition, the sprinkled water melts the icy road unevenly, so that the surface of the icy road becomes uneven and the roundness is lowered. Therefore, the thickness of the water film becomes uneven.

In the test step, a braking test on ice is performed on a wet icy road surface while maintaining the second room temperature. As a result, it is possible to accurately evaluate the braking performance on ice on a wet icy road surface without being affected by temperature changes.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view conceptually showing an example of an on-ice test apparatus used to implement the method for evaluating braking performance of a tire on ice according to the present invention; 1 is a flow chart explaining a method for evaluating braking performance on ice of a tire according to the present invention. (a) to (c) are cross-sectional views for explaining movements of a rotational drive step, a separation step, and a lateral movement step in a test process. (a) to (c) are graphs showing the "μs characteristics" of tires A, B, and C on a dry ice road surface and a wet ice road surface.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail.
As shown in FIG. 1, an on-ice test apparatus 1 for carrying out the method for evaluating braking performance on ice of a tire of the present invention (hereinafter sometimes simply referred to as "evaluation method") is installed in a temperature-controllable room. be done. The on-ice test apparatus 1 also includes a cylindrical driving drum 2 having an inner peripheral surface 2s for forming an icy road surface S. As shown in FIG.

In this example, an on-ice test apparatus 1 comprises the drive drum 2 , drum support means 3 and tire support means 4 .

The drive drum 2 comprises a steel cylindrical drum body 2A and a side wall 2B closing one side of the drum body 2A. The other side of the drum main body 2A is provided with an opening 5 for loading and unloading the test tire T, and the peripheral edge of the opening 5 is provided with a flange portion 5f having a small height.

The drum support means 3 supports the drive drum 2 so as to be rotatable around a horizontal axis j2. The drum support means 3 of this embodiment includes a support shaft 3A fixed at one end to the side wall 2B of the driving drum 2, a support base 3B rotatably supporting the support shaft 3A via a bearing, and the support shaft 3B. and drive means 3C for rotationally driving the shaft 3A. The driving means 3C includes a motor M, and by controlling the rotational speed of the motor M, the rotational speed of the drive drum 2 is adjusted.

The tire support means 4 supports the test tire T rotatably around a horizontal axis jT while bringing the outer peripheral surface of the test tire T into contact with the icy road surface S with a predetermined load. The tire support means 4 of this embodiment comprises a base 10, a support 11 supported on the base 10 so as to be movable in the axial direction of the drum, and a support attached to the support 11 via a cylinder 12 so as to be vertically movable. It comprises an arm 13 and a horizontal tire support shaft 14 connected to the lower end of the support arm 13 via a bearing.

By vertically moving the support arm 13 by the cylinder 12, the tire support means 4 can press the test tire T rotatably held on the tire support shaft 14 against the icy road surface S with a predetermined load. , the amount of load at that time can be adjusted.

Further, the support arm 13 is provided with a tire speed control means 15 capable of freely controlling the rotational speed of the tire support shaft 14 and the running speed of the test tire T. As shown in FIG. The tire speed control means 15 includes, for example, a well-known motor and brake. A load sensor (not shown) for measuring the vertical load Fz and the longitudinal force Fx acting on the test tire T is attached to the tire support shaft 14 . As the load sensor, for example, a sextometor is preferably employed.

Next, the evaluation method will be explained. As shown in FIG. 2, the evaluation method includes an ice surface formation process KA and a test process KB.

In the icy surface forming process KA, the icy surface S is formed on the inner peripheral surface 2s of the driving drum 2 in the state of the first room temperature t1 below the freezing point (0° C.) inside the room. Specifically, the ice road formation process KA comprises three stages KA1-KA3 in the present example.

At stage KA1, an ice floe is formed on the inner peripheral surface 2s. Specifically, by injecting water onto the inner peripheral surface 2s while rotating the drive drum 2, an ice floe is formed. Preferably, water is injected into the inner peripheral surface 2s while rotating the drive drum 2 at a high speed (for example, the speed of the inner peripheral surface 2s is 50 to 120 km/h). Then, the injected water is frozen at the first room temperature t1 while being evenly adhered to the inner peripheral surface 2s by centrifugal force. By repeating this process, an ice floe with an ice thickness of 20 to 50 mm, for example, is formed.

In step KA2, the surface of the ice floe formed in step KA1 is cut and smoothed with a cutting blade. Preferably, while rotating the drive drum 2, the surface of the ice floe is thinly scraped off, for example, by moving the cutting bit little by little in the axial direction of the drum.

In step KA3, the surface of the ice floe smoothed in step KA2 is polished with a polishing tire to a mirror surface. A slick tire or studless tire is preferably employed as the polishing tire. While the drum is rotating, a polishing tire is pressed against the surface of the ice floe to reduce surface roughness and form an ice road surface S with a mirror surface.

In order to efficiently form the icy road surface S in the icy road forming process KA, the first room temperature t1 is preferably in the range of -3 to -8°C. If the temperature is higher than -3°C, it takes a long time to form the icy road surface S, resulting in a decrease in efficiency. Conversely, when the temperature is lower than -8°C, cracks are likely to occur on the icy road surface S when the test step KB is performed at the second room temperature t2.

Next, the test process KB includes a wet ice road surface forming step KB1 in which the icy road surface S is a wet ice road surface Sw, and a test step KB2 in which an on-ice braking test of the test tire is performed using the wet ice road surface Sw.

In the wet ice surface forming stage KB1, the interior of the room is set to a second room temperature t2 higher than the first room temperature t1. As a result, the surface of the icy road surface S is melted to form a wet icy road surface Sw with a water film formed on the surface. At this time, the surface of the icy road surface S is naturally and gradually melted by the second room temperature t2. Therefore, the surface of the icy road surface S can be melted uniformly over the entire circumference while preventing cracks or the like from occurring on the icy road surface S. For uniformity, the drive drum 2 is preferably rotated during the wet ice road formation stage KB1. At this time, if the rotation speed is too high, it will take time for the water film to form due to the cooling effect. Therefore, in the wet ice road formation stage KB1, the speed of the inner circumferential surface 2s is preferably 1 to 10 km/h.

The second room temperature t2 is preferably 5 to 10° C. higher than the first room temperature t1. If the temperature difference (t2-t1) is as small as 5.degree. Conversely, if the temperature exceeds 10° C., the temperature difference becomes too large, and cracks are likely to occur on the icy road surface S in the test stage KB2. For the same reason, the second room temperature t2 is preferably in the range +1 to +3°C.

The thickness of the water film on the wet ice surface Sw formed in the wet ice surface forming step KB1 is preferably 0.5 to 1.0 mm. As a result of experiments conducted by the present inventor, particularly when the second room temperature t2 is in the range of +0.5°C to +2.0°C, the surface temperature of the icy road surface S rises only to about -0.3°C. It was confirmed that a water film of 0.5 to 1.0 mm can be stably formed.

The test phase KB2 is performed at the same second room temperature t2 as the wet ice surface formation phase KB1.

The test stage KB2 is not particularly restricted, but in this example includes a rotation drive step KB2 ₁ , a measurement step KB2 ₂ , a separation step KB2 ₃ , a lateral movement step KB2 ₄ , and a calculation step KB2 ₅ . Further, the rotation driving step _KB2-1 , the separation step KB2-3 _, and the lateral movement step _KB2-4 are sequentially repeated for a plurality of cycles.

In the rotation driving step KB21, the drive drum ₂ and the test tire T are rotated relative to each other while the outer peripheral surface of the test tire T is pressed against the wet ice road surface Sw.

In the measurement step _KB2-2 , the reaction force applied to the test tire T from the wet ice road surface Sw during the rotation drive step _KB2-1 is measured.

In the separation step _KB23 , the test tire T is separated from the wet ice road surface Sw.

In the lateral movement step _KB24 , the test tire T separated from the wet ice road surface Sw is laterally moved in the axial direction of the drum.

After a plurality of cycles of the rotation drive step _KB2-1 , the measurement step _KB2-2 , the separation step KB2-3 _, and the lateral movement step _KB2-4 , the ice braking performance is evaluated. This evaluation is performed based on the calculation result of calculation step _KB25 for calculating the coefficient of friction from the reaction force measured in measurement step _KB22 . The calculation step _KB25 can be performed for each cycle. It can also be performed after a predetermined number of cycles have been performed.

Specifically, first, the freely rotatably supported test tire T is pressed against the wet ice surface Sw of the drive drum 2 that is rotated at a predetermined speed (for example, 20 km/h). As a result, the test tire T rotates at the same speed as the driving drum 2 . After that, the test tire T is braked by the tire support means 4, and the speed of the test tire T is reduced from 20 km/h to 10 km/h at a rate of, for example, 5 km/h per second (rotational driving step KB2 ₁ ). .

In the rotation driving step KB21, the pressure of the test load is maintained for ₂ seconds or more and 10 seconds or less after the vertical load acting on the test tire T from the drive drum 2 reaches the value specified as the test load. is preferred. This stabilizes the rotation of the test tire T. After that, the test tire T is braked to decelerate.

At that time, the vertical load Fz and the longitudinal force Fx, which are reaction forces acting on the test tire, are continuously measured by the load sensors (measurement step KB2 ₂ ).

A coefficient of friction μ between the test tire T and the wet icy road surface Sw is calculated from the vertical load Fz and the longitudinal force Fx (calculation step KB2 ₅ ).
The coefficient of friction μ is expressed by the following formula.
μ = Fx/Fz

FIG. 3 shows the movement of the test tire T in the rotational drive step KB2 ₁ , the separation step KB2 ₃ and the lateral movement step KB2 ₄ . After completion of the measurement step _KB22 , the test tire T is lifted by the cylinder 12 and separated from the wet ice road surface Sw (Fig. 3(a)). Until the next pressing, the test tire T is kept away from the wet ice surface Sw for a predetermined time. During this separation, the test tire T is laterally moved in the axial direction of the drum (Fig. 3(b)). The test tire T is lowered by the cylinder 12 at the laterally moved position and pressed against the wet ice surface Sw (Fig. 3(c)). Then, the rotation drive step _KB2-1 , the measurement step _KB2-2 , the separation step KB2-3 _, and the lateral movement step _KB2-4 are repeated for a plurality of cycles.

By including the lateral movement step _KB24 in this way, the ground-contacting portion of the test tire T does not match the ground-contacting portion of the test tire T in the immediately preceding cycle. This prevents the formation of ruts. The distance L of lateral movement of the test tire T in the lateral movement step _KB24 is preferably in the range of 5 to 20 mm.

Then, the braking performance on the wet ice road surface Sw is evaluated based on the coefficient of friction calculated in at least some of the cycles.

In this example, the maximum friction coefficient μmax of the test tire T is obtained for each cycle in the calculation step _KB25 , and the braking performance on the wet icy road surface Sw is evaluated based on the average value of the maximum friction coefficient μmax in each cycle. be done. As for the average value of the maximum friction coefficient μmax, it is preferable to remove the maximum and minimum from the maximum friction coefficient μmax of each cycle and average the remaining maximum friction coefficient μmax.

It is also preferable to measure the thickness of the water film on the wet icy road surface Sw before each cycle is started, that is, before the test tire T is lowered. When the thickness of the water film exceeds 1.0 mm, it is preferable to adjust the thickness by removing water until the thickness falls within the range of 0.5 to 1.0 mm.

Although the particularly preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the illustrated embodiments and can be modified in various ways.

According to the method for evaluating braking performance on ice according to the present invention, five types of commercially available studless tires were used as test tires T1 to T5 to evaluate braking performance on a wet ice road surface Sw.

In the ice surface forming step KA, water is injected while rotating the drive drum 2 at a speed of 100 km/h in the state of the first room temperature t1 (-5° C.), and the water is applied to the inner peripheral surface 2s by centrifugal force. Freeze while sticking. By repeating this, an ice floe with an ice thickness of 40 mm was formed (step KA1).

Thereafter, while rotating the driving drum 2 at a speed of 80 km/h, the cutting bit was moved little by little in the axial direction of the drum to thinly scrape and smooth the surface of the ice floe (step KA2).

After that, in the rotating state (speed of 80 km/h), a polishing tire (commercially available studless tire) was pressed against the surface of the ice floe to mirror-finish the surface (step KA3).

In the test process KB, the rotational driving step KB2 ₁ , the measuring step KB2 ₂ , the separating step KB2 ₃ , and the lateral moving step KB2 ₄ are repeated for five cycles (N=5) for each of the test tires T1 to T5. was

Specifically, after performing 5 cycles of the test tire T1, 5 cycles of the test tire T2, 5 cycles of the test tire T3, and 5 cycles of the test tire T4 were performed, and each time, 5 cycles of the test tire T1 were performed again. .

In the wet ice surface formation stage KB1 of the test process KB, the room temperature is set to the second room temperature t2 (+2° C.), and after about 1.5 hours, the wet ice surface Sw with a water film thickness of 1.0 mm is formed. was formed. In this wet ice surface forming stage KB1, the drive drum 2 is rotated at a speed of 5 km/h.

In the rotation driving step KB21, in _each cycle, a freely rotatable test tire having an internal pressure (230 kPa) is pressed against the wet ice surface Sw of the driving drum 2 rotating at a speed of 20 km/h with a vertical load (3.8 kN). By doing so, the test tire was rotated at the same speed. After that, the brake was applied to the test tire in this pressed state, and the speed of the test tire was reduced from 20 km/h to 10 km/h at a rate of 5 km/h per second.

Further, in the calculation step _KB25 , the maximum friction coefficient μmax is calculated for each cycle from the vertical load Fz and the longitudinal force Fx measured in the measurement step _KB22 . Table 2 shows the results.

In Table 2, the average value of the maximum friction coefficient μmax is the average value of the maximum friction coefficient μmax of the remaining 3 cycles after removing the maximum and minimum among the maximum friction coefficient μmax of 5 cycles.

As shown in Table 2, each test tire T1 to T4 has a coefficient of variation (standard deviation σ/average value AVE) of 3% or less. Moreover, the difference between the first average value (0.115) and the second average value (0.116) of the test tire T1 is 0.001, and it can be confirmed that there is reproducibility.

1 Ice test device 2 Drive drum 2s Inner peripheral surface KA Ice surface formation process KA1 to KA3 Stage KB Test process KB1 Wet ice surface formation stage KB2 Test stage KB2 ₁ rotation drive step KB2 ₂ measurement steps KB2 ₃ separation steps KB2 ₄ lateral movement steps KB2 ₅ calculation step Sw Wet icy road surface S Icy road surface T Test tire t1 First room temperature t2 Second room temperature

Claims (6)

A method of evaluating the braking performance of a tire on ice using an ice road frozen on the inner peripheral surface of the driving drum of an on-ice test apparatus having a cylindrical driving drum and installed indoors, comprising:
The method for evaluating the braking performance on ice of the tire includes an ice surface formation step and a test step,
The ice surface formation step includes:
creating an ice surface on the inner peripheral surface of the driving drum in a first room temperature state in which the inside of the room is below freezing;
The test step includes:
The driving drum is rotated so that the speed of the inner peripheral surface of the driving drum is 1 to 10 km/h, and the inside of the chamber is set to a second room temperature of +0.5 to +2.0° C. higher than the first room temperature. a wet ice road surface forming step of forming a wet ice road surface in which a water film having a thickness of 0.5 to 1.0 mm is formed on the surface of the ice road surface by setting the state of
A method for evaluating a tire's braking performance on ice , comprising a test step of performing an on-ice braking test of the tire under the condition of the second room temperature and on the wet ice road surface. The method for evaluating braking performance on ice of a tire according to claim 1, wherein the first room temperature is in the range of -3 to -8°C. The step of forming an ice surface includes forming an ice floe on the inner peripheral surface;
a step of smoothing the surface of the formed ice floe by scraping it with a cutting blade;
3. The method for evaluating braking performance on ice of a tire according to claim 1, further comprising the step of polishing the smoothed surface of the ice floe to a mirror surface with a polishing tire. The test step includes:
a rotational driving step of relatively rotating the drive drum and the test tire while the outer peripheral surface of the test tire is pressed against the wet ice road surface;
a measuring step of measuring a reaction force applied to the test tire from the wet ice road surface during the rotating step;
a spacing step of spacing the test tire from the wet ice road surface;
a lateral movement step of laterally moving the test tire away from the wet ice road surface in the axial direction of the drum;
a calculation step of calculating a coefficient of friction from the reaction force measured in the measurement step;
Moreover, the rotational driving step, the measuring step, the separating step, and the lateral moving step are sequentially repeated for a plurality of cycles,
4. The method for evaluating tire braking performance on ice according to any one of claims 1 to 3, wherein braking performance on a wet ice road surface is evaluated based on the coefficient of friction calculated in at least some of the cycles. 5. The method for evaluating braking performance on ice of a tire according to claim 4, wherein in said lateral movement step, the lateral movement distance of said test tire is 5 to 20 mm. In the rotating step, the test load is maintained for 2 seconds or more and 10 seconds or less after the vertical load acting on the test tire from the driving drum reaches a value specified as the test load. 6. The method for evaluating braking performance on ice of the tire according to 4 or 5.

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