JP6288762B2 - Predicting tire block wear - Google Patents

Description

  The present invention relates to a tire block wear prediction method.

  Conventionally, it has been known that tires in which a block pattern is used for a tread may cause step wear on the block with long-term use. A method for predicting step wear in the block is proposed in Japanese Patent Laid-Open No. 2000-177326. This prediction method is a method using the ratio of the wear energy and the ratio of the slip amount between the ground contact portion and the ground contact portion of the ground contact surface of the block. The ground contact portion is a portion of the ground contact surface of the block that first contacts the road surface during rolling of the tire, and is also referred to as a first landing portion. The ground contact portion is a portion of the ground contact surface of the block that contacts the road surface lastly when the tire rolls, and is also referred to as a rear landing portion.

  In the evaluation method described above, the wear energy serving as an evaluation index is obtained by the formula Σ (in-plane stress × slip amount). Further, it is known that the amount of slip has a larger contribution rate to the wear energy than the in-plane stress.

  In the technique of the above-mentioned document, regarding the prediction of H & T wear (hill and toe wear), the ratio between the wear energy at the contact point and the wear energy at the contact point and the slip amount at the contact point and the slip amount at the contact point Ratio is used as an indicator. The ratio of the wear energy at the ground contact portion to the wear energy at the ground contact portion is close to 1, indicating that the H & T wear resistance is good. That is, the ideal H & T wear resistance is that the wear energy in the ground contact portion of the block is uniform from the ground contact portion to the ground contact portion.

  However, in recent years, for tires with improved wear resistance, prediction of H & T wear due to slippage and wear energy is often misplaced. This is because the H & T wear is different from a relatively wide range of wear forms such as shoulder wear and crown wear, and is local wear at the ground contact portion in the block, and the generation mechanism is also different.

JP 2000-177326 A

  The present invention has been made in view of the above-described present situation, and an object of the present invention is to provide a tire block wear prediction method capable of accurately and easily predicting H & T wear that may occur in a tire tread block. .

The method for predicting wear of a tire block according to the present invention includes:
A method of predicting wear of a tire tread block by rolling a test tire on a test road surface,
A slip amount measuring step of continuously measuring a slip amount with respect to the test road surface of the measurement target position on the ground contact surface of the block; and
A slip speed calculating step for calculating a slip speed with respect to the road surface of the measurement target position based on the measured slip amount and the time required for the slip;
A wear prediction step for predicting the wear of the block of the tire tread on the basis of the sliding speed.

Preferably, in the slip speed calculation step, the slip speed with respect to the test road surface of the measurement target position is:
Slip speed = (Slip amount in the in-plane direction parallel to the test road surface at the position to be measured)
÷ (time from start to end of slip),
It is calculated by the following formula.

Preferably, the block is a shoulder block located at a shoulder portion of a tire tread,
The measurement target position is a portion of the ground contact surface of the shoulder block that is to be attached to the road surface in the tire circumferential direction.

  Preferably, in the slip amount measuring step, the slip amount is measured in a state where a braking force is applied to the tire that is rolling on the test road surface.

  Preferably, in the slip amount measuring step, the normal force acting on the test road surface by the measurement target position is continuously measured in time, and based on the change in the measurement value, the start of the slip of the measurement target position is started. Identify the time and end time.

  Preferably, in the slip amount measuring step, a slip angle is set for the test tire.

  Preferably, a camber angle is set for the test tire in the slip amount measuring step.

Preferably, the measurement of the slip amount is performed using a bench test apparatus,
In this bench test apparatus, the test tire rolls on a transparent test road surface,
The displacement of the pressure measurement point is measured by a displacement sensor arranged on the back side of the test road surface.

  Preferably, in the wear prediction step, a reference value for the slip speed is set, and a tire having a slip speed obtained in the slip speed calculating step smaller than the reference value is determined as a tire having high wear resistance.

  According to the tire block wear prediction method of the present invention, H & T wear can be predicted with high accuracy and ease.

FIG. 1A is a partially cutaway front view showing an example of a bench wear energy test apparatus that can be used in the method of predicting wear of a tire block according to the present invention, and FIG. It is the partially cutaway side view seen in the IB-IB line direction of (a). FIG. 2 is a plan view showing a ground contact shape with respect to a test road surface of a test tire mounted on the test apparatus of FIG. FIG. 3 is a cross-sectional view showing a shoulder portion of a tire in which H & T wear occurs, in which the shoulder portion is cut by a plane parallel to the equator plane. FIG. 4A is a partial front view showing an example of a ground contact state of a shoulder block of a rolling tire, and FIG. 4B is a ground contact of a tire shoulder block loaded with a braking force during rolling. It is a partial front view which shows an example of a state. FIG. 5 is a graph schematically showing a change over time such as slipping from the time when the ground contact portion on the ground contact surface of the rolling tire shoulder block contacts the test road surface until it leaves the ground. FIG. 6 is a graph showing a change over time such as a slip from a time when a ground contact portion on a contact surface of a shoulder block of a rolling tire starts to slide with respect to a test road surface.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

[Slide speed of shoulder block]
The prediction of the H & T wear of the tire rolling on the road surface is performed based on the sliding speed of the ground contact portion of the shoulder block with respect to the ground road surface. This is because it has been found that the H & T wear is local wear of the ground contact portion in the block, and that the cause is due to “slip” of the ground contact portion with respect to the ground road surface. This slip is a short-time “slip” with respect to the road surface, which occurs when the contact portion of the shoulder block deformed at the time of ground contact returns to its shape (the shape is restored) at the moment when the ground contact is released.

The slip speed referred to here is the slip speed at the position to be measured on the contact surface of the tire with respect to the road surface. The slip speed is a quotient obtained by dividing the measured value of the slip amount at the measurement target position by the time (measured value) required for the slip amount to be generated. That is,
Slip speed = (Slip amount in the in-plane direction parallel to the test road surface at the measurement target position) ÷
(Time from slip start to slip end) ・ ・ ・ ・ ・ ・ ・ ・ (1)
It is calculated by the following formula (1). The time from the start of the slip to the end of the slip is also referred to as the slip time.

[Measurement position]
The measurement target position is a position on the ground contact surface of the shoulder block, which is a measurement target of the slip amount and the slide time. The measurement target position is a “ground contact portion” on the ground contact surface, and is set at a portion on the shoulder side. More specifically, the measurement target position is a position 80% outside the ground contact width from the center (position corresponding to the equatorial plane) in the tire width direction among the ground contact portions in the tire circumferential direction. The measurement target position is set in this way because “H & T wear” in the market is caused by more wear at the ground contact portion than at the ground contact portion. Even in the ground contact portion, wear appears significantly on the shoulder side. Therefore, the part on the shoulder side of the ground contact portion was set as the measurement object. For the measurement of the amount of sliding and the sliding time, a test tire and the following table-top wear energy test apparatus are used.

[Table wear energy test equipment]
An outline of the test apparatus 1 is shown in FIGS. FIG. 1A is a front view of the test apparatus 1, and FIG. 1B is a partially cutaway side view seen in the direction of line IB-IB in FIG. The test apparatus 1 supports a gantry 2, a test road surface 3 installed horizontally on the gantry 2, a rail 4 laid along the test road surface 3, and a test tire T. A traveling device 5 capable of traveling, a feed screw mechanism 6 installed on the gantry 2 in parallel to the rails 4 for traveling the traveling device 5, and a sensor unit 7 provided on the test road surface 3 are provided. doing.

  The traveling device 5 has a leg portion 8 that straddles the test road surface 3. The traveling device 5 includes a fixing nut (not shown) that is screwed into the rotary screw rod 9 of the feed screw mechanism 6. The traveling device 5 can travel along the rail 4 by the rotation of the rotary screw rod 9. The traveling device 5 includes a tire support portion 11 that supports the test tire T so as to be able to rotate, stop rotation, and reversely rotate at an upper position facing the test road surface 3.

  The tire support 11 can apply a braking force to the rolling test tire T. The tire support part 11 is movable up and down. By the downward movement of the tire support portion 11, the test tire T is pressed onto the test road surface 3, and a load is applied to the test tire T. The tire support portion 11 can set the camber angle by inclining the supported test tire T to the left and right with respect to the vertical plane including the equator plane EQ (FIG. 1B). It is possible to set the slip angle by rotating around the vertical axis passing through.

  In the sensor unit 7, the test road surface is transparent. As the test road surface 3a in the sensor unit 7, a transparent road surface made of a transparent acrylic plate, a transparent glass plate or the like can be adopted. A sensor box 12 below the transparent road surface 3a is provided with a three-component force sensor 13 as a load sensor. The detection end 13a of the load sensor 13 is exposed upward from the detection hole 14 formed in the transparent road surface 3a. The detection end 13a of the load sensor is pressed by the rolling test tire T. At this time, the three-component force sensor 13 has a vertical load (a load in the Z-axis direction) and a horizontal load (a load in the X-axis direction and a load in the Y-axis direction) applied to the test road surface 3 from the measurement target position MP (FIG. 2). Is detected over time. From these loads, the ground pressure and in-plane stress of the ground contact portion 22 (FIG. 4) on the ground surface of the shoulder block 20 described later are calculated. The elapsed time from the start of measurement is recorded in parallel with the load measurement. It is necessary to align in advance so that the measurement target position of the rolling test tire T is in contact with the detection end 13a of the three-component force sensor 13.

  The sensor box 12 is further provided with a camera 15 as a slip sensor. A measurement mark 16 is attached to the measurement target position MP of the test tire T. The camera 15 captures the displacement of the position of the center of gravity of the mark 16 continuously from below (hereinafter also referred to as “over time”). The camera 15 images at least a part of the ground plane including the measurement target position MP from immediately before the measurement target position MP contacts the detection end 13a of the load sensor 13 to immediately after the contact is released. The elapsed time from the start of measurement is recorded in parallel with the measurement of displacement. The “displacement” refers to displacement in the X-axis direction and the Y-axis direction in a plane parallel to the test road surface.

  In the test apparatus 1, the test road surface 3 is fixed, and the traveling device 5 that supports the test tire T is movable along the test road surface 3. However, it is not limited to such a configuration. Conversely, the test tire may be supported by a fixed support device, and the test road surface may be configured to be movable so as to roll the grounded tire.

[Measurement conditions of slip amount and slip time]
The load applied to the test tire T is set in a range of 0.3 to 0.6 times LI (Load Index = standard specified maximum load). This is because H & T wear in the market tends to occur at low load. If the load is too large, the entire ground contact surface of the block may be worn. When the entire ground contact surface of the block is worn, the height of the block is lowered and H & T wear is less likely to occur. Therefore, the load is reduced to prevent extreme early wear. The internal pressure of the test tire after assembling the rim is set to the standard-specified maximum internal pressure.

  A slip angle (SA) is preferably set for the test tire. This is because even if the applied load is light, the shoulder portion on one side of the tread can be sufficiently grounded. The slip angle is not less than the vehicle toe reference value. If the slip angle is less than the vehicle toe reference value, the measurement target position of the shoulder block may not be properly grounded. As a result, the reproducibility of H & T wear may be reduced.

  It is preferable that a camber angle (CA) is set for the test tire. This is because even if the load applied is light, the shoulder on one side is sufficiently grounded. The camber angle is greater than or equal to the vehicle reference value. If the camber angle is less than the vehicle reference value, the measurement target position of the shoulder block may not be properly grounded. As a result, the reproducibility of H & T wear may be reduced.

  The test tire is preferably loaded with a braking force. The braking force is set to 0.2G. 0.2 G is 0.2 times the vertical load G (0.3 LI to 0.6 LI) with respect to the test tire. Brake is applied so that a backward horizontal force of 0.06LI to 0.12LI is applied to the rolling test tire. The load of the braking force is to increase the slip of the ground contact portion of the shoulder block. That is, it aims at improving the reproducibility of H & T wear.

[Explanation of slip phenomenon]
FIG. 2 is a plan view showing a ground contact shape FG with respect to the test road surface 3 of the test tire T attached to the test apparatus 1 of FIG. In this figure, the test tire T is set with a camber angle that tilts to the left with respect to the vertical direction and a slip angle that tilts to the right with respect to the front. By setting the camber angle and the slip angle, as shown in the figure, the left shoulder block is firmly grounded, and the grounding shape SB becomes clear. FIG. 2 shows a position EG corresponding to the ground contact portion of the ground contact surface of the shoulder block, a position OG corresponding to the ground contact portion, a measurement target position MP and its mark 16.

  FIG. 3 is a graph showing the height distribution of the contact surface of the shoulder block 20 of a tire in which H & T wear has occurred due to long-term use. For ease of understanding, the size of the step due to wear is shown larger than the length of the ground contact surface of the block 20 in practice. Reference numeral 21 is a ground contact portion, and reference numeral 22 is a ground contact portion. As shown in the drawing, the ground contact portion 22 is more worn than the ground contact portion 21 on the ground surface. As a result, a step is generated in the shoulder block 20.

  FIG. 4 schematically shows a state of deformation of the shoulder block 20 portion of the test tire T rolling on the test road surface 3. In FIG. 4, in order to clearly show the deformation direction, many lines that are not actually present on the shoulder block are drawn. FIG. 4A shows the shoulder block 20 of the tire T during normal driving (during normal rolling), and FIG. 4B shows the shoulder block of the tire T when braking force is applied during driving. 20 is shown. In both figures, an arrow A indicates the traveling direction of the tire T, and an arrow B indicates the rotational direction of the tire.

  In FIG. 4B, the tire T is moving forward while the rotational speed and the traveling speed are decreased by braking. Therefore, the deformation direction (deflection direction) of the shoulder block 20 during braking is opposite to the deformation direction of the shoulder block 20 during non-braking rolling shown in FIG. The tire T is rotating in the counterclockwise direction for progress (FIGS. 4A and 4B). During braking, the shoulder block 20 has a faster traveling speed due to the forward movement of the vehicle body than a traveling speed due to the forward rotation of the tire T. Therefore, as shown in the figure, the deformation direction of the shoulder block 20 is reversed in the front-rear direction from the time of unbraking rolling shown in FIG.

  As shown in FIG. 4A, during normal running, the deformation of the shoulder block 20 is restored toward the rear when leaving the ground. That is, the ground contact portion 22 slides backward when the ground contact is released. As shown in FIG. 4 (b), the deformation of the shoulder block 20 is restored toward the front when the vehicle is separated from the ground during braking force load traveling. That is, the ground contact portion 22 slides forward when the ground contact is released. The maximum deformation is indicated by a two-dot chain line, and the slip direction which is a restoring direction of the deformation is indicated by an arrow C. In both cases of FIG. 4A and FIG. 4B, the slip amount of the ground contact portion 22 on the ground contact surface of the shoulder block 20 is larger than the slip amount of other portions. Compared to the normal rolling of the tire (FIG. 4A), the slip amount of the ground contact portion 22 is larger during braking (FIG. 4B). This is because the block receiving the braking force releases the deflection accumulated from the ground contact portion 21 at the ground contact portion 22 at a stretch.

  The graph of FIG. 5 shows the contact pressure, in-plane stress, displacement (slip amount), and wear during the period from when the ground contact portion 22 of the rolling tire shoulder block 20 touches the test road surface until it comes off the ground. The measurement record of each energy is shown. The vertical axis of the graph indicates the above items, and the horizontal axis indicates time.

  Here, the contact pressure is a contact pressure due to a vertical load received from the test road surface 3 by the measurement target position MP of the contact portion 22. The in-plane stress is stress (stress in the X-axis direction and stress in the Y-axis direction) along the plane parallel to the test road surface 3 at the measurement target position MP, which occurs in the shoulder block 20. The slip amount is the maximum displacement in the direction (X axis direction and Y axis direction) along the plane parallel to the test road surface 3 of the measurement target position MP. The wear energy is the product of the amount of slip at the measurement target position MP and the in-plane stress along the direction of the slip.

  As shown in FIG. 5, the slip of the measurement target position MP occurs near the end of grounding (separation from grounding) in time. That is, slip occurs with a decrease in ground pressure. Further, as shown in FIG. 5, the contact start time of the ground contact portion 22 is determined by the time when the rate of change (increase rate) in the ground pressure becomes maximum, and the time point when the ground contact portion 22 leaves the ground is This can be determined by the point in time when the pressure change rate (decrease rate) becomes maximum.

  FIG. 6 shows a displacement and a sliding speed from immediately before the ground contact part 22 is released to the ground immediately after the ground contact is released. FIG. 6 is a graph showing the sliding region in FIG. 5 in an enlarged manner. The slip area here means from the start of the slip to the end of the slip. In FIGS. 5 and 6, the start of the slip is the contact start time, and the end of the slip is the time when the measured displacement shows the maximum value. As shown in the figure, when the displacement increases at a constant rate, the sliding speed is constant (the curve indicating the sliding speed is substantially parallel to the horizontal axis).

[Get slip speed]
Six types of test tires A, B, C, D, E, and F having different formulations were prepared as follows. All of the test tires are summer tires having a size of 215 / 55R17. These six types of tires are tires having different results and evaluations of the H & T wear resistance performance in actual running tests performed in advance. This actual running test is a running test on a course mainly on a highway in which 80% or more of the total traveling distance is a highway. The height distribution of the contact surface of the shoulder block 20 was measured for each of the tires A, B, C, D, E, and F that had completed traveling for a predetermined distance. From this measurement result, the level difference was determined. The results are shown in Table 1.

  As shown in Table 1, the test tire A is a tire in which the maximum value of the shoulder block level difference is 0.8 mm in the result of the actual running test under the same conditions. The test tire B is a tire in which the maximum value of the shoulder block step amount was 0.5 mm in the above test. The test tire C is a tire in which the maximum value of the shoulder block step amount was 0.7 mm in the above test. The test tire D is a tire in which the maximum value of the shoulder block level difference is 1.4 mm in the above test. The test tire E is a tire in which the maximum value of the shoulder block level difference is 1.6 mm in the above test. The test tire F is a tire in which the maximum value of the shoulder block level difference was 1.3 mm in the above test.

  For each of the test tires A, B, C, D, E, and F, the slip amount and the slip time of the ground contact portion 22 of the shoulder block 20 were measured. The sliding speed is calculated by dividing the measured value of the slip amount by the measured value of the slip time. The purpose of this is to confirm the validity of the method for predicting the H & T wear resistance based on the sliding speed of the tire. The slip amount and slip time of these test tires were measured under the same conditions. For each tire A, B, C, D, E, and F, the calculated sliding speed was compared with the evaluation of the H & T wear resistance in the running test.

  The internal pressure of these samples is 230 kPa, the load is 3.51 kN, the braking force is 0.70 kN (0.2 G = 0.2 × 3.51 kN), the slip angle is −0.1 °, which is the vehicle toe reference value, The camber angle was set to −1.69 ° which is a vehicle reference value. The test tires A, B, C, D, E, and F were mounted on the bench wear energy test apparatus 1 shown in FIG. 1 and traveled (rolled) on the test road surface 3. The traveling speed is 3.5 m / min.

[Evaluation and prediction based on measurement results]
By the method described above, the sliding speeds of the ground contact portions of the six types of test tires A, B, C, D, E, and F were calculated. The sliding speed of each test tire is shown in Table 1. The actually measured sliding speed of each test tire is compared with the traveling test result (the shoulder block step amount). It can be seen from Table 1 that the tire block having a lower sliding speed has a smaller step amount of the shoulder block. That is, it is clear that the running test results for H & T wear correspond to the sliding speed of the shoulder block ground contact portion. From this measurement result, it is possible to predict that a tire having a small sliding speed at the ground contact portion of the shoulder block has less H & T wear and is excellent in H & T wear resistance. It can be judged that this prediction method is appropriate.

  It is possible to set a reference for predicting the H & T wear resistance performance of the tire based on the running test result and the sliding speed measurement result of each test tire shown in Table 1. For example, it is possible to set a threshold value that is a reference for predicting the quality of the H & T wear resistance. In other words, it is possible to determine whether the H & T wear resistance performance is good or bad.

  Alternatively, other criteria can be set in order to predict the quality of the H & T wear resistance. That is, as a determination criterion for pass / fail, a sliding speed value of one tire (for example, the test tire A) having good H & T wear resistance in a running test can be set.

  The tire block wear prediction method according to the present invention can be applied to various pneumatic tires.

DESCRIPTION OF SYMBOLS 1 ... Measuring apparatus 2 ... Mount 3 ... Test road surface 4 ... Rail 5 ... Traveling device 6 ... Feed screw mechanism 7 ... Sensor part 8 ... Leg part 9 ... -Rotating screw rod 10 ... Fixing nut 11 ... Tire support 12 ... Sensor box 13 ... Load sensor 14 ... Detection hole 15 ... Camera 16 ... Mark 20 ... Shoulder Block 21 ... Grounding part (of shoulder block) 22 ... Grounding part (of shoulder block) EG ... Grounding part FG ... Grounding shape MP ... Measurement target position OG ... Grounding Exit SB ... Shoulder block T ... Tire

Claims (9)

A method of predicting wear of a tire tread block by rolling a test tire on a test road surface,
A slip amount measuring step of continuously measuring a slip amount with respect to the test road surface of the measurement target position on the ground contact surface of the block; and
A slip speed calculating step for calculating a slip speed with respect to the road surface of the measurement target position based on the measured slip amount and the time required for the slip;
A tire block wear prediction method including a wear prediction step of predicting wear of a tire tread block using the slip speed as a criterion . In the slip speed calculation step, the slip speed with respect to the test road surface of the measurement target position is:
Slip speed = (Slip amount in the in-plane direction parallel to the test road surface at the position to be measured)
÷ (time from start to end of slip),
The tire block wear prediction method according to claim 1, which is calculated by the following formula. The block is a shoulder block located in the shoulder portion of the tire tread,
The method for predicting wear of a tire block according to claim 1 or 2, wherein the measurement target position is a portion of the ground contact surface of the shoulder block that is to be attached to the road surface in the tire circumferential direction.   The wear of the tire block according to any one of claims 1 to 3, wherein, in the slip amount measuring step, the slip amount is measured in a state where a braking force is applied to the tire rolling on the test road surface. Prediction method.   In the above slip amount measuring step, the normal force acting on the test road surface is measured continuously in time, and based on the change in the measured value, the start and end of the slip of the measurement target position The method for predicting wear of a tire block according to any one of claims 1 to 4, wherein a time point is specified.   The tire block wear prediction method according to any one of claims 1 to 5, wherein a slip angle is set for the test tire in the slip amount measurement step.   The tire block wear prediction method according to any one of claims 1 to 6, wherein a camber angle is set for the test tire in the slip amount measuring step. The above slip amount is measured using a bench test device,
In this bench test apparatus, the test tire rolls on a transparent test road surface,
The tire block wear prediction method according to any one of claims 1 to 7, wherein the displacement of the pressure measurement point is measured by a displacement sensor disposed on the back side of the test road surface.   In the wear prediction step, a reference value of a slip speed is set, and a tire having a slip speed obtained in the slip speed calculation step smaller than the reference value is determined as a tire having high wear resistance. The tire block wear prediction method according to claim 8.

Images