JP5462723B2 - Evaluation method of braking performance on tires on ice - Google Patents

Description

  The present invention relates to a method for evaluating the braking performance on ice of a tire that can evaluate the braking performance on ice of a tire with high accuracy.

  For example, Patent Document 1 below discloses a method for evaluating the performance of a tire on ice. In this evaluation method, a cylindrical drum having an inner peripheral surface as an icing road surface is used, the rotation speed of the drum is made constant, and the traveling speed of a tire traveling on the icing road surface is gradually reduced and braked, At that time, the relationship between the friction coefficient μ generated between the tire and the icing road surface and the slip ratio S of the tire is measured, thereby evaluating the braking characteristics of the tire on ice.

  However, when continuously reducing the tire running speed in this way, the vertical load fluctuates under the situation where the longitudinal force changes greatly, so the friction coefficient μ cannot be accurately measured, and the μ-S characteristic However, for example, as shown in Comparative Example 4 in FIG. 7B, there is a problem that the braking performance on ice cannot be evaluated with high accuracy, for example, it is far from the actual vehicle.

  Therefore, the present inventor has proposed to perform step braking in which the tire traveling speed is decelerated step by step instead of continuously decelerating and measure the friction coefficient and the slip ratio at each step of deceleration. However, in this case, a new problem to be solved occurs as shown below.

  In other words, when the travel speed reduction range is small, the travel test time until the tire stops is prolonged, and the ice on the frozen road surface is melted by frictional heat, causing a change in the road surface condition. This makes it difficult to accurately measure the friction coefficient. Particularly where the slip ratio is higher than 50%, the melted water becomes a resistance and the longitudinal force increases, so the friction coefficient tends to be measured higher than that of the actual vehicle test. When the deceleration range is large, although the change in the road surface state is small, it becomes impossible to measure at or near the peak of the friction coefficient, and similarly, it is impossible to accurately evaluate the braking performance on ice. In each stage of deceleration, the vertical load, the longitudinal force, and the traveling speed are not stable for about the first 20 seconds of each traveling time Δt, and an error occurs in the friction coefficient and the slip ratio.

JP 2007-076787

  Accordingly, the present invention provides tire braking by first step braking in which the speed is gradually reduced by a small first reduction width and second step braking in which the speed is gradually reduced by a large second speed reduction width. As a basic rule, while measuring reliably at or near the peak of the friction coefficient, it is possible to reduce the time of the entire running test and suppress changes in road surface conditions, and to improve the accuracy of measuring the friction coefficient and slip ratio. An object of the present invention is to provide a method for evaluating the braking performance on ice of a tire that can be accurately evaluated.

In order to solve the above-mentioned problem, the invention of claim 1 of the present application is a braking system that brakes a tire traveling on an icing road surface while rotating a cylindrical drum having an inner peripheral surface as an icing road surface at a constant speed Vo. procedure,
A measurement procedure for measuring a friction coefficient μ and a slip ratio S with respect to an icing road surface of the tire being braked,
And an evaluation procedure for evaluating braking performance on ice using the measured friction coefficient μ and slip ratio S, and
The braking procedure includes a first step braking in which a tire traveling on the icing road surface is decelerated stepwise from an initial speed va to an intermediate speed vb at a step speed v for each first deceleration width Δv1; A second step braking in which the speed from the intermediate speed vb to the stopped state or substantially stopped state is gradually reduced at a step speed v for each second deceleration width Δv2 larger than the first deceleration width Δv1; and In each stage of deceleration, the vehicle travels a traveling time Δt of 40 seconds or more and 60 seconds or less at each step speed v,
In the measurement procedure, at each stage of deceleration, the vertical load Fz, the longitudinal force Fx, and the step speed v acting on the tire are measured over time of the travel time Δt, and the following equations (1), (2) Is used to calculate the friction coefficient μ and the slip ratio S over time,
μ = Fx / Fz --- (1)
S = (Vo−v) / Vo −−− (2)
In the evaluation procedure, the friction coefficient μ and the slip ratio S obtained from the vertical load Fz, the longitudinal force Fx, and the step speed v measured after 30 seconds in the travel time Δt for each stage of deceleration. And averaging step for obtaining an average friction coefficient μ0 and an average slip ratio S0 for each stage of deceleration,
And an evaluation step for evaluating the braking performance on ice from a μ0-S0 curve obtained by plotting the average friction coefficient μ0 and the average slip ratio S0.

  In the invention of claim 2, in the evaluation step, the average slip ratio S0 is plotted on the X axis and the average friction coefficient μ0 is plotted on the Y axis to obtain a μ0-S0 curve, and the section in which the average slip ratio S0 is 0 to 50%. The braking performance on ice is evaluated by the area between the μ0-S0 curve and the X axis.

  In the invention of claim 3, the speed Vo of the drum is selected from a range of 25 to 35 km / h, the initial speed va is selected from a range of 98 to 95% of the speed Vo, The deceleration width Δv1 is selected from a range of 1.25 to 1.75 km / h, and the second deceleration width Δv2 is selected from a range of 2 to 2.5 times the first deceleration width Δv1, The intermediate speed vb is selected from an integer multiple of the first deceleration width Δv1 and a range of 55 to 65% of the speed Vo.

  As described above, according to the present invention, as a braking procedure, the initial speed va to the intermediate speed vb are gradually reduced at a step speed v for each small first deceleration width Δv1. That is, on the low slip ratio side where the change in the friction coefficient is large and the peak of the friction coefficient appears, it is possible to measure closely with a small deceleration width, so that the peak of the friction coefficient or the vicinity thereof can be captured. Further, the intermediate speed vb is gradually reduced at a step speed v for each large second deceleration width Δv2. In other words, on the high slip ratio side where the change in the friction coefficient is small, it is possible to measure roughly with a large deceleration range, so the time required for the entire running test can be shortened, and the change in road surface condition and the accompanying measurement error are generated. It can be kept low.

  In the evaluation procedure, the friction coefficient μ and the slip ratio S obtained from the vertical load, the longitudinal force and the step speed v measured after 30 seconds are averaged out of the traveling time Δt in each stage of deceleration. An averaging step for obtaining the average friction coefficient μ0 and the average slip ratio S0 for each stage is included. As described above, the first 20 seconds of the running time Δt is a range in which the vertical load, the longitudinal force, and the running speed are not stable. Therefore, the vertical load, the longitudinal force measured after 30 seconds avoiding this range. The step speed is stable with few errors, and the average friction coefficient μ0 and average slip ratio S0 obtained by averaging the friction coefficient μ and the slip ratio S obtained from these are stable values with further error reduction. It can be. Therefore, the μ0-S0 curve obtained by plotting the average friction coefficient μ0 and the average slip ratio S0 approximates the μ-S curve obtained by the on-ice braking test on the actual vehicle, and more accurately evaluates the on-ice braking performance of the tire. be able to.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view conceptually showing an on-ice test apparatus for carrying out a method for evaluating on-ice braking performance of a tire according to the present invention. It is a graph which shows an example of a braking procedure. (A), (B) is a graph which shows the relationship between the friction coefficient (micro | micron | mu) measured in the step of 5% of slip ratio, and travel time (DELTA) t, and the relationship between slip ratio S and travel time (DELTA) t. (A), (B) is a graph which shows the relationship between the up-and-down load Fz measured in the step of 5% of slip ratios, and traveling time (DELTA) t, and the relationship between the longitudinal force Fx and traveling time (DELTA) t. It is a graph which shows a μ0-S0 curve. (A)-(C) are the graphs which show the μ0-S0 curve in Example 1 and Comparative Examples 1-2. (A) is a graph showing a μ0-S0 curve in Comparative Example 3, and (B) is a graph showing a μ-S curve in Comparative Example 4. It is a graph which shows the relationship between the area G between (micro | micron | mu) 0-S0 curve and an X-axis in the area of an average slip rate of 0 to 50%, and the ABS braking distance of a real vehicle.

  Hereinafter, embodiments of the present invention will be described in detail. FIG. 1 is a side view conceptually showing an on-ice test apparatus 1 for carrying out the method for evaluating the braking performance on ice of a tire according to the present invention. The on-ice test apparatus 1 has an inner peripheral surface as an icing road surface 2s. The outer peripheral surface of the tire T is brought into contact with the icing road surface 2s with a predetermined load with respect to the cylindrical drum 2, the drum support means 3 that rotatably supports the drum 2 around a horizontal axis j2, and the frozen road surface 2s. And a tire support means 4 that rotatably supports the tire T around a horizontal axis jT.

  The drum 2 includes a steel cylindrical drum main body 2A and a side wall body 2B that closes one side surface of the drum main body 2A. The other side surface has an opening 5 for taking in and out the tire T and the opening. A flange portion 5 f having a small height is provided on the periphery of 5.

  The drum support means 3 includes a support shaft 3A having one end fixed to the side wall 2B of the drum 2, a support base 3B that rotatably supports the support shaft 3A via a bearing, and the support shaft 3A. Driving means 3C for rotationally driving the motor. The driving means 3C includes a motor M, and the rotational speed of the drum 2 is adjustable by controlling the rotational speed of the motor M.

  A smooth icing road surface 2s continuous in the circumferential direction is formed on the inner peripheral surface side of the drum body 2A. The icing road surface 2s is formed by injecting water while rotating the drum 2 after setting the room temperature of the laboratory where the on-ice testing apparatus 1 is set to 0 ° C. or lower (for example, −5 ° C.). Specifically, water is appropriately injected into the drum 2 while rotating the drum 2 in a high-speed rotation region where the speed of the inner peripheral surface is in the range of 50 to 100 km / h. Then, the injected water is frozen while being evenly attached to the inner peripheral surface by centrifugal force, and an ice plate having an ice thickness of, for example, 20 to 50 mm is formed by repeating this. Thereafter, the surface of the ice disk is thinly scraped off with a cutting tool while the drum is rotating, thereby forming a smooth icing road surface 2 s concentric with the drum 2.

  In the present example, the tire support means 4 includes a base 10, a support base 11 supported on the base 10 so as to be slidable in the drum axis direction, and the support base 11 via a cylinder 12. A support arm 13 that is freely attached, and a horizontal tire support shaft 14 that is coupled to the lower end of the support arm 13 via a bearing are provided. The tire support means 4 moves the support arm 13 up and down by the cylinder 12 to press the tire T held rotatably on the tire support shaft 14 against the ice road surface 2s with a predetermined load. In addition, the load amount at that time can be adjusted.

  The support arm 13 is provided with tire speed control means 15 that can freely control the rotational speed of the tire support shaft 14 and thus the traveling speed of the outer peripheral surface of the tire T. The tire speed control means 15 includes, for example, a known motor and braking device. Further, a load sensor for measuring the vertical load Fz and the longitudinal force Fx acting on the tire T, in this example, a 6-component force meter, is attached to the tire support shaft 14.

  Next, a method for evaluating the braking performance on ice of the tire will be described. In this evaluation method, a braking procedure for braking the tire T traveling on the icing road surface 2s while rotating the drum 2 having an inner circumferential surface of the icing road surface 2s at a constant speed Vo (a peripheral speed Vo of the icing road surface 2s). Evaluation of braking performance on ice is performed using K1, a measurement procedure K2 for measuring the friction coefficient μ and the slip ratio S with respect to the icing road surface 2s of the tire T being braked, and the measured friction coefficient μ and the slip ratio S, respectively. An evaluation procedure K3 is provided.

  In the braking procedure K1, step braking is performed in which the traveling speed of the tire T is not decelerated continuously but decelerated step by step. Specifically, as shown in FIG. 2, the tire T traveling on the icing road surface 2s is gradually decelerated from the initial speed va to the intermediate speed vb at a step speed v for each first deceleration width Δv1. The first step braking K1A to be performed and the intermediate speed vb to the stop state or substantially stopped state are stepwise decelerated at a step speed v for each second deceleration width Δv2 that is larger than the first deceleration width Δv1. Second step braking K1B is performed.

  In general, the friction coefficient μ of a tire on an icy road surface varies greatly when the slip ratio S is in the range of 0 to 30%, and the peak of the friction coefficient μ tends to appear when the slip ratio S is in the range of 5 to 10%. . Accordingly, the initial speed va to the intermediate speed vb are gradually reduced at the step speed v for each small first deceleration width Δv1, and the low slip where the change of the friction coefficient μ is large and the peak of the friction coefficient μ appears. By measuring the rate side closely, it is possible to accurately detect a change in the friction coefficient μ. On the other hand, from the intermediate speed vb to the stopped state or substantially stopped state, the speed is gradually reduced at the step speed v for each large second deceleration width Δv2, and the high slip ratio side where the change in the friction coefficient is small. Measure roughly. As a result, it is possible to shorten the time for the entire running test while maintaining the detection accuracy, and it is possible to reduce changes in road surface conditions such as melting of ice due to friction, and errors resulting therefrom. Naturally, when the intermediate speed vb is a multiple of the second deceleration width Δv2, the intermediate speed vb is gradually reduced from the intermediate speed vb to the stop state, but the intermediate speed vb is reduced to the second deceleration width Δv2. If it is not a multiple of, the speed is gradually reduced to a multiple of the second deceleration width Δv2 that is closest to the stop state, that is, to a substantially stop state.

  For this purpose, the initial speed va is selected from a range of 98 to 95% of the speed Vo of the frozen road surface 2s of the drum 2, and the intermediate speed vb is selected from a range of 55 to 65% of the speed Vo. It is preferable to do this. When the initial speed va is smaller than 95% of the speed Vo and the intermediate speed vb is larger than 65% of the speed Vo, it is difficult to capture a large change in the friction coefficient μ and its peak. On the other hand, if the intermediate speed vb is less than 55% of the speed Vo, the time required for the entire driving test is not sufficiently shortened, and it becomes difficult to sufficiently suppress changes in road surface conditions. In view of speed control, the initial speed va is set within a range of 98 to 95% of the speed Vo and a value obtained by subtracting the first deceleration width Δv1 from the speed Vo (va = Vo−Δv1). Is more preferable.

  The first deceleration width Δv1 is selected from the range of 1.25 to 1.75 km / h, and the second deceleration width Δv2 is 2.0 to 2.5 times the first deceleration width Δv1. It is preferable to select from the range. When the first deceleration width Δv1 is smaller than 1.25 km / h, the road surface is polished for a long time in a state where the friction coefficient is high, so the road surface condition changes to the side where the friction coefficient decreases, On the other hand, if it exceeds 1.75 km / h, the deceleration width is too rough, and it becomes difficult to capture large changes and peaks in the friction coefficient μ. On the other hand, if the second deceleration width Δv2 is less than twice the first deceleration width Δv1, the time required for the entire running test increases unnecessarily, causing a change in road surface conditions such as melting ice, and conversely 2.5. If it exceeds twice, the measurement interval is too coarse, which adversely affects detection accuracy.

  As the speed Vo of the drum 2, a range of 25 to 35 km / h can be preferably employed as in the conventional case. In FIG. 2, the speed Vo = 30 km / h, the initial speed va = 28.5 km / h (that is, va / Vo = 0.95), the intermediate speed vb = 18 km / h (that is, vb / Vo = 0). .60), and a preferred range of deceleration width Δv1 = 1.5 km / h and deceleration width Δv2 = 3.0 km / h (that is, Δv2 / Δv1 = 2.0) is shown.

  In the braking procedure K1, the traveling time Δt of 40 seconds or more and 60 seconds or less is caused to travel at each step speed v at each stage of deceleration.

Next, in the measurement procedure K2, the vertical load Fz, the longitudinal force Fx, and the step speed v acting on the tire T are measured for each stage of deceleration with the lapse of the travel time Δt. ) And (B), the friction coefficient μ and the slip ratio S are calculated over time. The friction coefficient μ and the slip ratio S can be calculated using the following equations (1) and (2).
μ = Fx / Fz --- (1)
S = (Vo−v) / Vo −−− (2)
Here, when the traveling speed of the tire T is decelerated stepwise, in each stage of deceleration, the vertical load Fz, the longitudinal force Fx, and the traveling speed are in the first 20 seconds of each traveling time Δt. It tends to be unstable. 4A and 4B show the vertical load Fz and the longitudinal force Fx measured at the stage of the initial speed va (that is, the stage of the slip rate 5%), and the vertical load is in the range of 0 to about 20 seconds. It can be confirmed that Fz and the longitudinal force Fx are not stable. Therefore, the friction coefficient μ and the slip ratio S calculated from the vertical load Fz, the longitudinal force Fx, the traveling speed also vary within the range of 0 to about 20 seconds as shown in FIGS. 3 (A) and 3 (B). Tend to occur.

  Therefore, in the braking procedure K1, it is necessary to stabilize the friction coefficient μ and the slip ratio S by setting the travel time Δt to 40 seconds or more. However, if the traveling time Δt is too long, the time of the entire traveling test is increased, causing a change in road surface condition. Therefore, the upper limit of the travel time Δt is restricted to 60 seconds or less.

  Next, in the evaluation procedure K3, for each stage of deceleration, the friction coefficient μ obtained from the vertical load Fz, the longitudinal force Fx, and the step speed v measured after 30 seconds in the travel time Δt. And an average step K3A for obtaining an average friction coefficient μ0 and an average slip ratio S0 for each stage of deceleration by averaging the slip ratio S and the slip ratio S, and a plot of the average friction coefficient μ0 and the average slip ratio S0. -An evaluation step K3B for evaluating the braking performance on ice from the S0 curve.

  As described above, the first 20 seconds of the traveling time Δt is a range in which the vertical load Fz, the longitudinal force Fx, and the traveling speed are not stable. Therefore, the average friction coefficient μ0 and the average slip ratio S0 obtained by averaging the friction coefficient μ and the slip ratio S obtained from the vertical load Fz and the longitudinal force Fx and the step speed v measured after 30 seconds avoiding this range, respectively. Is a stable value with less error, and can be a representative friction coefficient and slip ratio at each stage of deceleration. From the viewpoint of accuracy, the travel time Δt is preferably 40 seconds or more and 50 seconds or more.

  The representative friction coefficient, the average friction coefficient μ0 that is the slip ratio, and the μ0-S0 curve (illustrated in FIG. 5) obtained by plotting the average slip ratio S0 are μ-S obtained by the on-ice braking test on the actual vehicle. It approximates a curve, and the braking performance on ice of the tire can be more accurately evaluated.

  In the evaluation step K3B, the average slip rate S0 is plotted on the X axis and the average friction coefficient μ0 is plotted on the Y axis to obtain a μ0-S0 curve, and the μ0-S0 curve in the section where the average slip rate S0 is 0 to 50%. The braking performance on ice can be quantified and evaluated by the value of the area G between the X axis and the X axis. By digitizing in this way, it becomes possible to compare the braking performance on ice between tires of different sizes and types.

  As mentioned above, although especially preferable embodiment of this invention was explained in full detail, this invention is not limited to embodiment of illustration, It can deform | transform and implement in a various aspect.

  The on-ice braking performance of a commercially available radial tire for a passenger car (tire size 195 / 65R15) was tested with the specifications shown in Table 1 using the on-ice test apparatus shown in FIG. For each stage of deceleration, an average friction coefficient μ0 and an average slip ratio S0 are obtained, and μ0-S0 curves obtained by plotting the average friction coefficient μ0 and the average slip ratio S0 are respectively shown in FIGS. It shows. The room temperature of the laboratory and the temperature of the icing road surface are −5 ° C., the internal pressure of the tire is 200 kPa, and the load applied to the tire is matched with the load applied to the front tire of the vehicle in the braking test of the actual vehicle described later. It was set to 4.24 kN.

  For comparison, substantially the same tire is mounted on all wheels of a vehicle (passenger car 2000cc, FR car) under the condition of an internal pressure of 200 kPa, and smoothed at an initial speed of 30 km / h in an environment of a temperature of -5 ° C. A braking test was conducted in a state in which the vehicle entered a frozen road surface and ABS was enabled. And while calculating a vehicle speed using a non-contact speedometer, the speed of a wheel tire is calculated from the rotation pulse of an ABS signal, and from these results, a μ-S characteristic in an actual vehicle is obtained, and the above-mentioned test apparatus on ice is used. The obtained μ0-S0 curve was compared.

  Next, on the three types of tires (sample tires 1 to 3) having different tread patterns, an on-ice braking performance test is performed according to the specifications of Example 1 using the on-ice test device, and a μ0-S0 curve is obtained. It was. Then, an area G between the μ0-S0 curve and the X axis in a section where the average slip ratio S0 is 0 to 50% was obtained and evaluated by an index with the sample tire 1 being 100. In addition, a braking test of an actual vehicle was performed on the sample tires 1 to 3 to obtain a braking distance, and evaluation was performed using an index with the sample tire 1 being 100. Then, as shown in FIG. 8, the results were plotted and compared in a coordinate system in which the evaluation based on the on-ice braking performance test using the on-ice test apparatus was plotted on the Y axis, and the evaluation based on the actual vehicle braking test was plotted on the X axis.

  As shown in FIGS. 6 and 7, in the case of Example 1, it can be confirmed that a μ0-S0 curve close to the μ-S characteristic of the actual vehicle can be obtained. Further, in the case of Comparative Example 1, it can be confirmed that since the step braking is one and the deceleration width Δv is narrow, the ice is melted at an early stage and the road surface state is changed, so that an accurate friction coefficient cannot be measured. Particularly in the vicinity of a slip rate of 20%, the road surface is polished for a long time with a high friction coefficient. As a result, the friction coefficient is lower than the μ-S characteristic of the actual vehicle. The melted water acts as a resistance to increase the longitudinal force Fx, and the friction coefficient appears apparently large. Further, in the case of the comparative example 2, since there is one step braking and the deceleration range Δv is wide, a large change or peak of the friction coefficient cannot be captured, and an accurate friction coefficient cannot be measured. Further, in the case of Comparative Example 3, since there is only one step braking although it has an appropriate deceleration width Δv, as in Comparative Example 1, the ice melts during the test and the road surface condition changes, and an accurate friction coefficient is obtained. Cannot be measured. In the case of Comparative Example 4, since the tire running speed is continuously decelerated, the vertical load also fluctuates under the situation where the longitudinal force changes greatly, so the friction coefficient cannot be measured accurately.

  When the area G between the μ0-S0 curve and the X axis in the section where the average slip ratio S0 is 0 to 50% (for convenience, it may be referred to as the area G of the μ0-S0 curve) is used as an index. As shown in Fig. 5, the performance on ice close to the braking test of an actual vehicle using ABS can be shown. That is, it is possible to predict the ABS braking performance of a tire without performing a braking test on an actual vehicle.

2 drum 2s icing road surface K1 braking procedure K1A first step braking K1B second step braking K2 measurement procedure K3 evaluation procedure K3A averaging step K3B evaluation step T tire

Claims (3)

A braking procedure for braking a tire traveling on the icing road surface while rotating a cylindrical drum having an inner peripheral surface as an icing road surface at a constant speed Vo;
A measurement procedure for measuring a friction coefficient μ and a slip ratio S with respect to an icing road surface of the tire being braked,
And an evaluation procedure for evaluating braking performance on ice using the measured friction coefficient μ and slip ratio S, and
The braking procedure includes a first step braking in which a tire traveling on the icing road surface is decelerated stepwise from an initial speed va to an intermediate speed vb at a step speed v for each first deceleration width Δv1; A second step braking in which the speed from the intermediate speed vb to the stopped state or substantially stopped state is gradually reduced at a step speed v for each second deceleration width Δv2 larger than the first deceleration width Δv1; and In each stage of deceleration, the vehicle travels a traveling time Δt of 40 seconds or more and 60 seconds or less at each step speed v,
In the measurement procedure, at each stage of deceleration, the vertical load Fz, the longitudinal force Fx, and the step speed v acting on the tire are measured over time of the travel time Δt, and the following equations (1), (2) Is used to calculate the friction coefficient μ and the slip ratio S over time,
μ = Fx / Fz --- (1)
S = (Vo−v) / Vo −−− (2)
In the evaluation procedure, the friction coefficient μ and the slip ratio S obtained from the vertical load Fz, the longitudinal force Fx, and the step speed v measured after 30 seconds in the travel time Δt for each stage of deceleration. And averaging step for obtaining an average friction coefficient μ0 and an average slip ratio S0 for each stage of deceleration,
An evaluation method for braking performance on ice of a tire, comprising: an evaluation step for evaluating braking performance on ice from a μ0-S0 curve obtained by plotting the average friction coefficient μ0 and the average slip ratio S0.   In the evaluation step, the average slip rate S0 is plotted on the X axis and the average friction coefficient μ0 is plotted on the Y axis to obtain a μ0-S0 curve, and the μ0-S0 curve and the X axis in the section where the average slip rate S0 is 0 to 50%. The method for evaluating the braking performance on ice of a tire according to claim 1, wherein the braking performance on ice is evaluated based on an area between them.   The drum speed Vo is selected from a range of 25 to 35 km / h, the initial speed va is selected from a range of 98 to 95% of the speed Vo, and the first deceleration width Δv1 is 1.25. The second deceleration width Δv2 is selected from a range of 2 to 2.5 times the first deceleration width Δv1, and the intermediate speed vb is selected from the first speed range Δb2. 3. The method for evaluating the braking performance on ice of a tire according to claim 1, wherein the speed is selected from an integer multiple of a deceleration width Δv1 and a range of 55 to 65% of the speed Vo.

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