JP2000177320A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the uncomfortable tire noise by setting each of specified- order amplitudes of specified-order amplitudes obtained by Fourier-transforming a pulse train with a specified expression by use of each pitch as unit pulse. SOLUTION: In a train of pitches arranged in the circumferential direction of a tire, each pitch consists of a unit pulse having an equal size. Taking one pitch as the start point, the pitch train is replaced by a pulse train with a space corresponding to the pitch length that is the circumferential length of each pitch in the order of the pitch arrangement. The pulse train is subjected to Fourier-transformations defined by expressions I, II and III. In the expressions, N represents the total number of pitches, X(j) represents the position of the j-th unit pulse in the pulse train, L represents the tire circumferential length variable, K represents a natural number of 1-2N, and S represents a natural number of 1-N. Of the resulting 1st to Kth-order amplitudes P(K), the 1st to Nth-order amplitudes P(S) satisfy the expression IV. According to this, the uncomfortable noise energy is effectively reduced to improve the noise performance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a pneumatic tire capable of improving noise performance.

[0002]

2. Description of the Related Art Generally, a tread pattern formed on a tread surface of a tire is formed by continuously repeating a pitch, which is a pattern constituent unit, in a tire circumferential direction. The pitch usually includes a groove. Therefore, when the tire is rolling, the compression and release of air in the groove and the impact sound with the road surface are periodically generated at each pitch or at each of the multiple pitches during this pitch, and pattern noise is generated by the pulse-like vibration. It is known to

Conventionally, in order to reduce the pattern noise, a plurality of types of pitches having different circumferential lengths are used, and these are arranged at random to disperse the pattern noise itself over a wide frequency band, thereby reducing white noise. The pitch variation method is becoming widely adopted,
The fact is that it has not yet produced a sufficient effect.

The present invention has been devised in view of the above problems, and provides a pneumatic tire which is based on a pitch variation method and which can further enhance its noise dispersion effect and reduce unpleasant tire noise. It is intended to be.

[0005]

According to one aspect of the present invention, there is provided a tread pattern in which N pitches constituting a pattern constituting unit are arranged in a tire circumferential direction on a tread surface. A pneumatic tire having
The row of the pitches arranged in the tire circumferential direction is replaced with a pulse train in which the pitch is a unit pulse and each pitch is a starting point and the pitch is the circumferential length of each pitch in the order of the arrangement and one pitch is a starting point. And a pulse train obtained by performing Fourier transform on the pulse train by the following equations (1) to (3).
Among the amplitudes P (K) of the th to the Kth order (K is a natural number from 1 to 2N), the amplitudes P (S) of the 1st to the Nth order satisfy the expression (4).

(Equation 4)

Here, the amplitudes P (K) of the 1st to Kth order are:
It is desirable to satisfy the following expression (5).

(Equation 5)

It is desirable that the first to K-order amplitudes P (K) also satisfy the following equation (6).

(Equation 6)

In the present specification, “pitch” means
As described above, the pattern constituent unit is formed in the pattern of the tread portion. For example, in the case of a block pattern, the block is composed of one block and one lateral groove adjacent to the block in the tire circumferential direction. If it is a pattern, it is configured as an area between valleys and valleys or between ridges and valleys of zigzag grooves extending in the tire circumferential direction, and if it is a rug pattern, one rug groove and one adjacent one of the rug grooves in the tire circumferential direction Each pitch constitutes one pitch with the land.

[0009]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a development view of a tread pattern of the pneumatic tire according to the present embodiment. In the figure, a tread surface 2 has a longitudinal groove 3 extending in the tire circumferential direction and a direction intersecting the longitudinal groove 3. An example is shown in which a plurality of blocks 5 divided by extending lateral grooves 4 are formed. In this example, the one block 5 and one lateral groove 4 adjacent to one side of the block in the tire circumferential direction are one as a pattern constituent unit of the tread pattern.
One of the pitches 7 is illustrated.

The pitch 7 has a plurality of types having different pitch lengths CL, for example, 5 different lengths in the circumferential direction.
And a pitch row 9 in which these pitches are arranged on the tread surface 2 so as to satisfy the requirements described later.
At least in one row, and in this example, five rows. In this example, the same pitch 7 is used for each pitch 7 adjacent in the tire axial direction.

The number of types of the pitch 7 is 3 to 10, preferably 3 to 8 in consideration of productivity, more preferably 3 to 8.
It is desirable to set it to 5. In addition, pitch 7 in one round of tire
If the total number N is too small, the effect of the pitch variation method is relatively reduced, and if it is too large, uneven wear easily occurs. For example, 45 or more, preferably 50 to 7
It is desirable to set it to about 0.

When the plurality of types of pitches 7 are arranged in the order of their pitch lengths, if the increase ratio of the pitch lengths between adjacent pitches is too large, the difference in rigidity becomes large, which tends to cause uneven wear. If it is too small, noise may concentrate on a specific frequency. From this point of view, the increasing ratio of the pitch length between the adjacent pitches is preferably in the range of 1.05 to 1.40, more preferably 1.10 to 1.30.

Further, as described above, in the tire of the present invention, the rows of the pitches 7 arranged in the tire circumferential direction are, as shown in FIG. Starting from one pitch 7, the pulse sequence is replaced with a pulse train in the order of the pitch arrangement and at intervals corresponding to the pitch length CL which is the circumferential length of each pitch 7. Further, such a pulse train is created over one circumference of the tire.

In FIG. 2, the vertical axis indicates the magnitude of the pulse, and the horizontal axis indicates the interval at which the unit pulse U occurs. Here, the unit pulse U is generated not at equal intervals but according to each pitch length CL. In this example, this is substituted by the pitch ratio PL. The “pitch ratio” defines one reference pitch which is a reference among a plurality of types of pitches, and is represented by a ratio of the length of each pitch to the length of the reference pitch. Preferably, the reference pitch is a middle pitch when all kinds of pitches are arranged in the order of length, or a pitch close thereto.

According to the present invention, this pulse train is of the 1st to Kth order (K is a natural number from 1 to 2N) obtained by the Fourier transform defined by the following equations (1), (2) and (3). Among the amplitudes P (K), amplitudes P (S) of the 1st to Nth orders (S is 1
(Natural numbers from to N) satisfy the following expression (4).

[0016]

(Equation 7)

The amplitude obtained by Fourier-transforming the pulse train obtained from the pitch arrangement of the tread pattern has a correlation with the noise energy obtained by analyzing the noise of the tire, and the order has a correlation with the frequency. By setting the amplitude P (S) to a predetermined value or less, frequency dispersion can be further promoted, and unpleasant noise energy is effectively reduced to improve noise performance. Note that amplitude values exceeding the K-th order have almost no effect when discussing the noise characteristics of the tire. Therefore, in the present embodiment, amplitudes from the 1st to the K-th order are targeted.

Here, "L" in the above formulas (1) and (2) is defined as a tire circumference variable, and is represented by the sum of the pitch ratios of all the pitches 7 over one circumference of the tire. Further, “X (j)” in equations (1) and (2) indicates a pulse position from the starting point to the j-th pitch.
It is expressed by the sum of the pitch ratios up to the th. X (1) = PL (1) X (2) = PL (1) + PL (2) ... X (j) = PL (1) + PL (2) + ... + PL
(J) Note that PL (i) (i is a natural number from 1 to N) indicates the value of the pitch ratio of the pitch arranged i-th from the starting point.

In general, a primary component, which is a main sound source of tire noise, often occurs near the order corresponding to the pitch number, that is, the Nth order when Fourier-transformed. Therefore, in the amplitude obtained by the Fourier transform, it is necessary to reduce at least the N-th order amplitude for white noise generation. However, since a first-order component may appear in the order near the N-th order, at least, 1 to N
By limiting each of the following amplitudes P (S) to a predetermined value or less, tire noise can be dispersed and noise performance can be improved.

Further, in the present embodiment, 1 to 4 obtained by Fourier-transforming the pulse train by the above equations (1) to (3) are used.
The amplitude P (S) up to the Nth order is limited to the value of "750 × N ^-1.1 " or less. This is obtained from various experimental results of the inventors. That is, a large number of tires with different numbers of pitches were prototyped, the amplitude values of the 1st to Nth orders were calculated, and the tires were mounted on an actual vehicle to perform a feeling noise test. Value P (S)
It was found that those having a value of 750 × N ^−1.1 or less exhibited good noise characteristics.

As shown in the following equation (5), the amplitude P (K) over a wide range from the 1st to the Kth order (K is a natural number from 1 to 2N) calculated from the pulse train by Fourier transform is represented by By setting the value to be equal to or less than the value of “750 × N ^−1.1 ”, it is desirable in that the effect of dispersing the frequency can be enhanced and the unpleasant noise energy can be more effectively reduced.

[0022]

(Equation 8)

In the conventional pitch variation method, there is generally no main regularity in how the frequency dispersion is scattered, so that even when the frequency is dispersed, it is physiologically unpleasant, such as noise from a television or radio. Synthetic sounds may be formed.

Generally, the "auditory characteristic" of a human is 20 Hz
Up to 20 kHz is considered to be a general audible range,
The sound in this range does not necessarily mean that the sound is heard with a uniform sensitivity. Especially 500Hz-5kHz,
In particular, the frequency band around 3 kHz to 4 kHz is a frequency band that is sensitively heard by humans, and it has been found that insensitive to high-frequency and low-frequency sounds, it exhibits insensitive hearing characteristics. Therefore, although the frequency is dispersed by the pitch variation method, if the sound energy of the above-mentioned sensitive frequency band is high, there is a possibility that the occupant may feel physiological discomfort.

As a result of the experiments by the inventors, in order to reduce such discomfort, it is necessary to reduce the noise energy in a sensitive frequency band. It has been found that it is preferable to provide a regularity that gradually decreases.

In the present embodiment, in order to provide the regularity of the stepwise decrease in the amplitude in the manner in which the frequency distribution of the tire noise is scattered, the 1-th to (K) th order obtained by Fourier-transforming the pulse train is used. The amplitude P (K) up to K is a natural number from 1 to 2N) is set to be equal to or less than (750 × N ^−0.1 ) / K as shown in the following equation (6). FIG.
7 to 7, etc., the curves of P = (750 × N ^−0.1 ) / K are shown by chain lines.

[0027]

(Equation 9)

As described above, since the amplitude P (K) of the 1st to Kth order also satisfies the expression (6), the frequency variance has a regularity of decreasing stepwise. This is particularly desirable in that it can effectively reduce physiologically unpleasant noise energy.

In such a pitch arrangement, for example, an arbitrary pitch arrangement order is set, a pulse train is obtained from this arrangement, Fourier transform is performed, and it is confirmed whether or not the above equations (4) to (6) are satisfied. Alternatively, for example, it is also possible to obtain an array in which the amplitude waveform that satisfies the expression (6) is converted into a discrete value and perform an inverse Fourier transform on the array to determine the array order.

In the above embodiment, the tread pattern forming the block pattern has been exemplified. However, the present invention can be applied to various tread patterns such as a rib pattern, a lug pattern, and a composite pattern in which two or more of these are combined. .

[0031]

[Example] The tire size is 195 / 55R15,
Test tires having pitch arrangement based on the specifications in Table 1 based on the block pattern shown in FIG. 1 were prototyped, and the noise performance of the tires was compared by an actual vehicle running test.

There are five types of pitches A to E shown below.
The total number N of pitches was 58. A pitch length: 24.4 mm, pitch ratio: 0.750 B pitch length: 28.4 mm, pitch ratio: 0.875 C pitch length: 32.5 mm, pitch ratio: 1.00 (reference) D pitch Length: 36.6 mm, pitch ratio: 1.125 E Pitch length: 40.6 mm, pitch ratio: 1.25 The “pitch ratio” indicates the pitch length of each pitch and the pitch length of pitch C. It is shown by a ratio of 1.

The noise performance is determined by the tire internal pressure (226 k
Pa), rim (15 × 6JJ), running road surface (asphalt), running vehicle (passenger car: 1600cc: FF, vehicle weight 1.3 ton), noise inside the vehicle when running under the conditions of speed 60km / H by the driver 5 depending on the feeling
The points were evaluated, and the higher the score, the better.
Table 1 shows the test results and the pitch arrangement order. Further, FIGS. 3 to 7 show graphs showing the relationship between the order K and the amplitude P obtained by the Fourier transform from the tread pattern of each test tire.

[0034]

[Table 1]

In Conventional Example 1 and Conventional Example 2, the amplitude P
(S), that is, 750 ×
Since an amplitude exceeding N- ^1.1 exists, no significant improvement in noise feeling is observed. In Examples 1 to 3,
In any case, since no amplitude exceeding 750 × N ^-1.1 exists between the 1st to 58 (N) orders, the noise feeling is improved by good frequency dispersion, especially the frequency dispersion near the 58th order. Can be confirmed. In particular, in the third embodiment, since the amplitudes P (K) up to the 1st to 116 (K) orders also satisfy the expression (6), they are dispersed with a certain regularity. It was confirmed that a very excellent noise feeling test result was obtained.

[0036]

According to the first or second aspect of the present invention, the dispersion of the frequency in the primary component of the tire noise is improved, and the noise characteristics can be greatly improved. According to the third aspect of the present invention, the frequency distribution of tire noise is scattered with regularity that changes stepwise, so that white noise suitable for human hearing characteristics is achieved, and noise discomfort is caused. Can be further reduced.

[Brief description of the drawings]

FIG. 1 is a development view of a tread pattern for explaining an embodiment of the present invention.

FIG. 2 is a diagram illustrating a pulse train.

FIG. 3 is a graph showing a relationship between orders obtained by Fourier transform of Example 1;

FIG. 4 is a graph showing the relationship between orders obtained by Fourier transform of Example 2;

FIG. 5 is a graph showing the relationship between orders obtained by Fourier transform of Example 3;

FIG. 6 is a graph showing a relationship between orders obtained by Fourier transform of Conventional Example 1;

FIG. 7 is a graph showing the relationship between orders obtained by Fourier transform of Conventional Example 2;

[Explanation of symbols]

 2 Tread surface 3 Vertical groove 4 Horizontal groove 5 Block B Block 7 Pitch CL Pitch length

Claims (3)

[Claims] 1. A pneumatic tire having a tread pattern in which N pitches constituting a pattern constituent unit on a tread surface are arranged in a tire circumferential direction, wherein a row of the pitches arranged in the tire circumferential direction is defined as each pitch. Is used as a unit pulse, and with one pitch as a starting point, the sequence is replaced with a pulse train separated by a pitch length which is the circumferential length of each pitch in the order of the above arrangement, and this pulse train is replaced by the following formulas (1) to (3) Of the amplitudes P (K) of the 1st to Kth order (K is a natural number from 1 to 2N) obtained by Fourier transform, the amplitudes P (S) of the 1st to Nth order satisfy Expression (4). A pneumatic tire characterized by the following. (Equation 1) 2. The pneumatic tire according to claim 1, wherein the first to Kth order amplitudes P (K) satisfy the following equation (5). (Equation 2) 3. An apparatus according to claim 1, wherein said first to K-order amplitudes P (K) satisfy the following equation (6).
The pneumatic tire as described. (Equation 3)