A pneumatic tire having a tire noise reduction system

Abstract

The present application relates to the technical field of tire manufacturing, and particularly relates to a pneumatic tire with a tire noise reduction system. The pneumatic tire with the tire noise reduction system comprises a tread, a bead, a sidewall, a carcass layer and a belt layer arranged at the radial outside of the carcass layer, the tread is composed of an upper tread and a lower tread, the upper tread is located on the surface of the tread part, the lower tread is arranged at the lower layer of the upper tread, the ratio of the thickness H1 of the lower tread to the total thickness H0 of the upper and lower treads is 0.2<=H1 / H0<=0.6, the lower tread is subjected to foaming treatment, the foaming porosity is controlled to be between 1% and 5%, and the foaming pore diameter is between 0.5 mu m and 5 mu m. The lower tread part of the tire is subjected to micro-foaming, and the tire noise is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of tire manufacturing technology, in particular to a pneumatic tire with a tire noise reduction system. BACKGROUND

[0002] In recent years, with the rise of electric vehicles, consumers have higher requirements for the comfort of using cars, and reducing tire noise during driving is a very important indicator.

[0003] With the good control of engine noise and body vibration noise of the car, the proportion of tire noise in the car noise has further expanded. When the vehicle speed exceeds 80km / h, tire noise becomes the main component of the vehicle driving noise. The faster the speed and the greater the load, the higher the energy level of the tire noise, and the larger the proportion in the vehicle driving noise. As the only part of the vehicle in contact with the ground, the noise radiation and vibration characteristics of the tire directly affect the comfort and stability of the car. Therefore, major automobile companies at home and abroad have carried out research on tire noise, and have put forward more stringent requirements for the noise of the matching tire.

[0004] At present, there are many methods to reduce noise, such as changing the pattern style or using the corresponding tread formula, but such methods either increase the cost or reduce the performance of the tire in other aspects.

[0005] The noise of the tire during driving is generally composed of external noise such as pattern noise and road noise, and internal cavity noise. Among them, the tire cavity noise is caused by the resonance of the super-low pressure sound system composed of the tire and the disc wheel, which is usually called tire resonance sound. The cavity noise frequency is between 200-300Hz, which is determined by the tire cavity structure. In the cavity inside the tire, the sound absorber made of sponge-like material is a known method to reduce cavity noise. The mechanism of sponge-like sound absorbing cotton as a sound absorber is that there are countless air holes in the sound absorbing cotton, which can buffer and absorb sound waves, so that sound waves are difficult to be reflected out of the sound absorbing cotton. Therefore, in the past patents, the density of the sound absorbing cotton is strictly regulated, such as the patent CN110395976A which stipulates that the density of the sound absorbing cotton needs to be between 40g / m3-50kg / m3, otherwise it cannot achieve effective results. However, the degree of reduction of cavity noise by this method still has a large space for improvement. Because the frequency of cavity noise is between 200-300Hz, and the pore size of polyurethane as a sound absorbing cotton material is generally fixed after foaming, it is difficult to eliminate sound waves in the entire frequency range.

[0006] Chinese invention patent application (publication number: CN110733298A publication date: 20200131) discloses a tire noise reduction device, which is mainly provided with a noise reduction structure on the inner surface of the tire cavity inside the tire, the noise reduction structure is provided with at least one sound-absorbing material, the sound-absorbing material penetrates to form a hollow air chamber, the sound-absorbing material includes a bonding surface adhered to the inner surface, and a through surface, a channel is arranged on the through surface to communicate the air chamber and face the center of the tire; due to the design of the sound-absorbing material provided with the air chamber, the energy of the sound wave is offset and attenuated, and the resonance sound of the tire cavity is effectively reduced.

[0007] At the same time, the applicant applied for a kind of tire noise reduction system (application number 2021104977114, application date: 20210508), including a pneumatic tire with a cavity, the pneumatic tire has a tread portion, a bead portion and a sidewall portion, the inner wall of the tread portion is bonded with a strip-shaped sound-absorbing cotton by an adhesive, the strip-shaped sound-absorbing cotton is provided with more than one continuous annular hole in the circumferential direction, the strip-shaped sound-absorbing cotton is connected end to end, and the annular hole is also connected end to end to form an annular large sound-absorbing cavity that does not communicate with the inner cavity of the tire. 3 -50kg / m 3 The side wall of the annular hole is connected with the pores of the strip-shaped sound-absorbing cotton, so that the annular large sound-absorbing cavity and a large number of porous sound-absorbing cavities are connected.

[0008] The above-mentioned patent also uses strip-shaped sound-absorbing cotton to reduce tire noise, and the applicant found in research that if the lower tread portion of the tread is micro-foamed, the tire noise can be further reduced, and there is no public disclosure in the prior art. SUMMARY

[0009] To solve the above technical problems, the purpose of the present application is to provide a pneumatic tire with a tire noise reduction system, the lower tread portion of the tire is micro-foamed, and the tire noise is reduced.

[0010] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0011] A pneumatic tire with a tire noise reduction system, including a tread, a bead, a sidewall, a carcass layer and a belt arranged on the radial outer side of the carcass layer, the tread is composed of an upper tread and a lower tread, the upper tread is located on the surface of the tread portion, and the lower tread is arranged below the upper tread, the ratio of the thickness H1 of the lower tread to the total thickness H0 of the upper and lower treads is 0.2≤H1 / H0≤0.6; the lower tread is foamed, the foaming porosity is controlled between 1%-5%, and the foaming pore size is between 0.5μm-5μm.

[0012] As a preference, the lower tread hardness is 55-68 HA, and the thickness needs to be limited to 2.0-6.0 mm.

[0013] As a preference, the lower tread is made by vulcanization of a rubber composition comprising the following raw materials:

[0014] 100 parts by weight of a rubber component and 1.0-10.0 parts by weight of (a) a foaming material, and (b) a reinforcing filler, wherein the total amount of components (a) and (b) is 30 to 130 parts by weight;

[0015] The foaming material is composed of foaming masterbatch particles and porous diatomite, and the mass ratio of the foaming masterbatch particles to the porous diatomite is 1:5-5:1; the foaming masterbatch particles adopt ethylene-propylene-diene rubber, and the chemical foaming agent adopts foaming capsules, and the mass ratio of the ethylene-propylene-diene rubber to the foaming capsules is 1:1-2:1; the porous diatomite is a fossil of freshwater algae, the particle size measured by a scanning electron microscope is 5-20 um, the nitrogen adsorption specific surface area NSA is 25-40 m 2 / g, and the pH value is close to neutral, and the columnar inorganic filler has a pore structure.

[0016] As a further preference, the rubber component is selected from natural rubber, solution-polymerized styrene-butadiene rubber 1 and solution-polymerized styrene-butadiene rubber 2; in parts by weight, the natural rubber is 20.0-30.0 parts, the solution-polymerized styrene-butadiene rubber 1 is 40.0-50.0 parts, and the solution-polymerized styrene-butadiene rubber 2 is 25.0-35.0 parts; the solution-polymerized styrene-butadiene rubber 1 has 30-40% styrene and 35-45% vinyl butadiene in the total weight of the polymer; and the solution-polymerized styrene-butadiene rubber 2 has 15-25% styrene and 50-60% vinyl butadiene in the total weight of the polymer.

[0017] As a further preference, the reinforcing filler includes, in parts by weight, white carbon black: 5.0-25.0 parts, and carbon black: 30.0-65.0 parts; the white carbon black is high-specific-surface-area white carbon black, and the nitrogen adsorption specific surface area NSA is between 145-250 m 2 / g; and the carbon black is super-wear-resistant carbon black, and has a high outer surface area (STSA) in the range of 100-129 m 2 / g.

[0018] As a further preference, the composition further includes 2.0-6.0 parts of a silane coupling agent, and the silane coupling agent is a thio-carboxylic ester silane with a mercapto group; preferably, the silane coupling agent is one of bis-[(triethoxysilyl)-propyl]tetrasulfide and bis-[(triethoxysilyl)-propyl]disulfide.

[0019] As more preferably, the composition further comprises 10-25 parts of environmentally friendly aromatic hydrocarbon oil, 2.0-5.0 parts of uniformizing agent, 2.0-8.0 parts of rubber active agent, 3.0-7.0 parts of rubber antioxidant, 1.0-3.0 parts of sulfur, and 1.5-4.0 parts of vulcanization accelerator.

[0020] As preferably, the inner wall of the carcass layer is provided with strip-shaped sound-absorbing cotton in the circumferential direction; the strip-shaped sound-absorbing cotton is a sponge-like porous material foamed from a high polymer material; the radial height of the tire between the bead base line and the equatorial point of the tire cavity is defined as the tire cavity height Hc, and the thickness of the strip-shaped sound-absorbing cotton is Hs, both of which need to satisfy 20mm < Hs < 0.2 x Hc.

[0021] As preferably, the strip-shaped sound-absorbing cotton is provided with more than one continuous annular hole in the circumferential direction, the strip-shaped sound-absorbing cotton is connected end to end, and the annular holes are also connected end to end to form an annular main sound-absorbing cavity not communicating with the tire cavity; the side wall of the annular hole communicates with the pores of the strip-shaped sound-absorbing cotton, so that the annular main sound-absorbing cavity and a large number of porous sound-absorbing cavities are connected in communication. The sound-absorbing cavity further weakens the vibration of sound waves in the tire cavity, thereby achieving the purpose of reducing noise.

[0022] As preferably, the line connecting the center of gravity of the annular hole and the center of the tire tread is perpendicular to the center auxiliary line of the cross-sectional width of the tire; the annular hole accounts for 10-50% of the cross-sectional area of the strip-shaped sound-absorbing cotton; and the apparent density of the strip-shaped sound-absorbing cotton is 5kg / m3-20kg / m3.

[0023] As preferably, the radius Rs of the center of the cross-sectional circle of the sound-absorbing cavity needs to satisfy 4.5mm < Rs < 0.5Hs-1mm.

[0024] The tire of the present application is micro-foamed in the lower tread part, thereby reducing tire noise. Further, the tire is foamed to produce a micro-porous structure by using a mixed method of chemical foaming and inorganic foaming. The inorganic foaming uses porous diatomite, and the chemical foaming uses foaming masterbatch to prevent the flammability of the chemical foaming agent from causing safety hazards in production, while controlling the amount of foaming masterbatch used to prevent the expansion rate of the foaming compound from being too large. Further, the present application also adopts the design of one or more large cylindrical holes in the sound-absorbing cotton, which are not communicated with the tire cavity and serve as the main sound-absorbing cavity; and the specific gravity of the sound-absorbing cotton material is increased, that is, the volume of the numerous small sound-absorbing cavities is reduced. Through the implementation of the present application, it is found that the design of the large main sound-absorbing cavity combined with numerous small sound-absorbing cavities can suppress cavity noise in a wide frequency range. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The figure is a structural schematic diagram of the present application.

[0026] Figure 2Structure diagram of embodiment 4 of the present application. DETAILED DESCRIPTION

[0027] The specific embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0028] As Figure 1 shown in a pneumatic tire with a tire noise reduction system, including a tread 1, a bead 2, a sidewall 3, a carcass layer 4 and a belt 5 arranged on the radially outer side of the carcass layer, the tread 1 is composed of an upper tread 11 and a lower tread 12, the upper tread 11 is located on the surface of the tread part, and the lower tread 12 is arranged on the lower layer of the upper tread 11, the ratio of the thickness H1 of the lower tread to the total thickness H0 of the upper and lower treads is 0.2≤H1 / H0≤0.6; the lower tread is foamed, the foaming porosity is controlled between 1%-5%, and the foaming pore size is between 0.5μm-5μm.

[0029] Because the lower tread 11 is too soft to be pressed and shaped by the capsule during vulcanization, and the rubber is too soft to affect the rigidity of the tire, resulting in a decrease in the handling performance of the tire, therefore, the ideal hardness is 55~68HA, and the hardness of the lower tread 11 is less than the hardness of the tread rubber, the difference is greater than or equal to 1HA, which can change the tire common frequency and reduce the noise of the tire in the low frequency range. In addition, the thickness of the lower tread rubber 11 needs to be limited within 2.0~6.0mm, exceeding 6.0mm will cause a significant decrease in the rigidity of the tread, affecting the handling response performance of the tire, and less than 2.0mm cannot reflect the role of the lower tread rubber.

[0030] Reference

[0031] The composition of the raw materials of the lower tread: 25.0 parts of natural rubber, 43.0 parts of solution styrene-butadiene rubber 1, 32.0 parts of solution styrene-butadiene rubber 2, 40.0 parts of white carbon black 1165MP, 22.0 parts of carbon black N234, 4.0 parts of silane coupling agent Si-75, 10.0 parts of environmentally friendly aromatic oil, 2.0 parts of antioxidant 6PPD, 0.7 parts of antioxidant TMQ, 1.5 parts of microcrystalline wax, 2.5 parts of zinc oxide, 1.3 parts of stearic acid, 4.0 parts of uniformizing agent, 2.0 parts of sulfur, 1.5 parts of accelerator CZ, and 1.0 parts of accelerator DPG.

[0032] Among them, the solution styrene-butadiene rubber 1: the combined styrene accounts for 36% of the total weight of the polymer, and the vinyl accounts for 40% of the total weight of butadiene; the solution styrene-butadiene rubber 2: the combined styrene accounts for 20% of the total weight of the polymer, and the vinyl accounts for 55% of the total weight of butadiene.

[0033] Example 1

[0034] The raw material composition of the under-tread: 25.0 parts of natural rubber, 43.0 parts of solution styrene-butadiene rubber 1, 32.0 parts of solution styrene-butadiene rubber 2, 40.0 parts of high-fraction white carbon black 1165MP, 22.0 parts of carbon black N234, 4.0 parts of silane coupling agent Si-75, 10.0 parts of environmentally-friendly aromatic oil, 3.5 parts of foaming masterbatch, 2.0 parts of porous diatomite, 2.0 parts of antioxidant 6PPD, 0.7 parts of antioxidant TMQ, 1.5 parts of microcrystalline wax, 2.5 parts of zinc oxide, 1.3 parts of stearic acid, 4.0 parts of homogenizing agent, 2.0 parts of sulfur, 1.5 parts of accelerator CZ, and 1.0 parts of accelerator DPG.

[0035] Among them, except for the foaming masterbatch and porous diatomite, the rest of the materials are the same as in the comparative example. During the processing of the rubber compound, the foaming masterbatch needs to be added in the sulfurization stage, and the sulfurization temperature should not exceed 100°C. The foaming masterbatch masterbatch uses a ternary ethylene-propylene-diene rubber, and the chemical foaming agent uses a foaming capsule. The mass ratio of the ternary ethylene-propylene-diene rubber to the foaming capsule is 1:2. Its characteristic is that at a high temperature of 140°C-180°C, the foaming capsule shell softens, the internal liquid hydrocarbon vaporizes, and the size of the capsule increases to achieve the effect of foaming. The porous diatomite is a freshwater algal fossil. The particle size measured by scanning electron microscopy is 5-20um, the nitrogen adsorption specific surface area (NSA) is 25-40m 2 / g, and the PH value is close to neutral. It is a cylindrical inorganic filler with a porous structure.

[0036] Example 2

[0037] The raw material composition of the under-tread: 25.0 parts of natural rubber, 43.0 parts of solution styrene-butadiene rubber 1, 32.0 parts of solution styrene-butadiene rubber 2, 40.0 parts of high-fraction white carbon black 1165MP, 22.0 parts of carbon black N234, 4.0 parts of silane coupling agent Si-75, 10.0 parts of environmentally-friendly aromatic oil, 3.5 parts of foaming masterbatch, 2.0 parts of porous diatomite, 2.0 parts of antioxidant 6PPD, 0.7 parts of antioxidant TMQ, 1.5 parts of microcrystalline wax, 2.5 parts of zinc oxide, 1.3 parts of stearic acid, 4.0 parts of homogenizing agent, 2.0 parts of sulfur, 1.5 parts of accelerator CZ, and 1.0 parts of accelerator DPG.

[0038] Among them, the materials and the processing of the rubber compound are the same as in Example 1.

[0039] Example 3

[0040] The under-tread raw material composition: 25.0 parts of natural rubber, 43.0 parts of solution styrene-butadiene rubber 1, 32.0 parts of solution styrene-butadiene rubber 2, 40.0 parts of high-fraction white carbon black 1165MP, 22.0 parts of carbon black N234, 4.0 parts of silane coupling agent Si-75, 10.0 parts of environmentally friendly aromatic oil, 3.5 parts of foaming masterbatch, 2.0 parts of porous diatomite, 2.0 parts of antioxidant 6PPD, 0.7 parts of antioxidant TMQ, 1.5 parts of microcrystalline wax, 2.5 parts of zinc oxide, 1.3 parts of stearic acid, 4.0 parts of homogenizing agent, 2.0 parts of sulfur, 1.5 parts of accelerator CZ, 1.0 parts of accelerator DPG.

[0041] Wherein, the material and the rubber processing are the same as in Example 1.

[0042] The structures of the above examples and the comparative examples 1-3 are the same, as shown in Figure 1 .

[0043] Example 4

[0044] The under-tread raw material in Example 1 is used, and the structure is increased on the basis of the structure of Figure 1 , as shown in Figure 2 .

[0045] The inner wall of the tire is provided with a strip-shaped sound-absorbing cotton 6 by means of an adhesive, and the strip-shaped sound-absorbing cotton 6 is a sponge-like porous material made of polyurethane foam, and the apparent density of the strip-shaped sound-absorbing cotton 6 is 20kg / m 3 , the cross section of the strip-shaped sound-absorbing cotton 6 is square, the height of the tire cavity is Hc is 41mm, and the thickness of the sound-absorbing cotton is Hs is 30mm. The strip-shaped sound-absorbing cotton 6 is provided with a continuous annular hole 7 in the circumferential direction, the annular hole 7 is circular in cross section, the annular hole cross section accounts for 30% of the cross section area of the strip-shaped sound-absorbing cotton, and the radius of the circle is Rs is 8mm. The center of gravity of the annular hole 7 and the center line of the tire tread are perpendicular to the center auxiliary line of the cross section width of the tire. The strip-shaped sound-absorbing cotton 6 is connected end to end, and the annular hole 7 is also connected end to end to form an annular main sound-absorbing cavity which does not communicate with the inner cavity of the tire; the side wall of the annular hole 7 is connected with the pores of the strip-shaped sound-absorbing cotton 6, so that the annular main sound-absorbing cavity and a large number of porous sound-absorbing cavities are connected.

[0046] Table 1: Related parameters of the rubber of the examples and comparative examples

[0047] Reference Example Example 1 Example 2 Example 3 Example 4 300% Modulus 14.7 Mpa 12.4 Mpa 13.7 Mpa 13.7 Mpa 12.4 Mpa Elongation at Break 360% 454% 424% 424% 454% Hardness 68 HA 63 HA 65 HA 65 HA 63 HA 60°C tan delta 0.121 0.049 0.061 0.061 0.049 Tread Noise 73.8 dB 72.6 dB 72.5 dB 70.6 dB 68.5 dB Rolling Resistance 7.5 7.0 6.9 7.0 7.0

[0048] The foregoing is a description of the embodiments of the present application. The above description of disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A pneumatic tire having a tire noise reduction system comprising a tread, a bead, a sidewall, a carcass layer, and a belt layer disposed radially outward of the carcass layer, characterized by, The tread is composed of an upper tread and a lower tread, the upper tread is located on the surface of the tread portion, and the lower tread is arranged under the upper tread; the ratio of the thickness H1 of the lower tread to the total thickness H0 of the upper and lower treads is 0.2≤H1 / H0≤0.6; the lower tread is subjected to foaming treatment, the foaming porosity is controlled to be between 1% and 5%, and the foaming pore diameter is between 0.5 μm and 5 μm; The lower tread has a hardness of 55-68 HA and a thickness limited to 2.0-6.0 mm; the lower tread is prepared by vulcanization of a rubber composition comprising the following raw materials: 100 parts by weight of a rubber component and 1.0-10.0 parts by weight of (a) a foaming material and (b) a reinforcing filler, wherein the total amount of the components (a) foaming material and (b) reinforcing filler is 30 to 130 parts by weight; The foaming material is composed of foaming parent rubber particles and porous diatomite, and the mass ratio of the foaming parent rubber particles and the porous diatomite is 1:5-5:1; the foaming parent rubber particles adopt ethylene-propylene-diene rubber, a chemical foaming agent adopts foaming capsules, and the mass ratio of the ethylene-propylene-diene rubber and the foaming capsules is 1:1-2:1; the porous diatomite is a freshwater algal fossil, the particle size measured by a scanning electron microscope is 5-20um, the nitrogen adsorption specific surface area NSA is 25-40m 2 / g, and the pH value is close to neutral, and the columnar inorganic filler has a porous structure. The rubber component is selected from natural rubber, solution-polymerized styrene-butadiene rubber 1 and solution-polymerized styrene-butadiene rubber 2; the natural rubber is 20.0-30.0 parts by weight, the solution-polymerized styrene-butadiene rubber 1 is 40.0-50.0 parts by weight, and the solution-polymerized styrene-butadiene rubber 2 is 25.0-35.0 parts by weight; the solution-polymerized styrene-butadiene rubber 1 contains 30-40% of styrene and 35-45% of vinyl groups based on the total weight of the polymer; the solution-polymerized styrene-butadiene rubber 2 contains 15-25% of styrene and 50-60% of vinyl groups based on the total weight of the polymer; the reinforcing filler includes 5.0-25.0 parts by weight of white carbon black and 30.0-65.0 parts by weight of carbon black; the composition further includes 2.0-6.0 parts by weight of a silane coupling agent, 10-25 parts by weight of an environmentally-friendly aromatic hydrocarbon oil, 2.0-5.0 parts by weight of a homogenizing agent, 2.0-8.0 parts by weight of a rubber active agent, 3.0-7.0 parts by weight of a rubber antioxidant, 1.0-3.0 parts by weight of sulfur and 1.5-4.0 parts by weight of a vulcanization accelerator; The inner wall of the carcass layer is provided with a strip-shaped sound-absorbing cotton in the circumferential direction; the strip-shaped sound-absorbing cotton is a sponge-like porous material prepared by foaming a high molecular material; the radial height of the tire between the bead base line and the equatorial point of the tire cavity is defined as the tire cavity height Hc, and the thickness Hs of the strip-shaped sound-absorbing cotton, which need to satisfy 20mm<Hs<0.2×Hc.

2. A pneumatic tire having a tire noise reduction system as defined in claim 1, wherein, Said white carbon is a white carbon with high specific surface area, with a nitrogen adsorption specific surface area NSA comprised between 145 and 250 m 2 / g; said carbon black is a super abrasion carbon black, with a high external surface area (STSA) comprised between 100 and 129 m 2 / g.

3. A pneumatic tire having a tire noise reduction system as defined in claim 2, wherein, The silane coupling agent is a thio-carboxylic ester silane with a mercapto group.

4. A pneumatic tire having a tire noise reduction system as defined in claim 3, wherein, The silane coupling agent is one of bis-[(triethoxysilyl)-propyl]tetrasulfide and bis-[(triethoxysilyl)-propyl]disulfide.

5. The pneumatic tire having a tire noise reduction system of claim 1, wherein, The strip-shaped sound-absorbing cotton is provided with more than one continuous annular hole in the circumferential direction, the strip-shaped sound-absorbing cotton is connected end to end, and the annular holes are also connected end to end to form an annular main sound-absorbing cavity which is not communicated with the inner cavity of the tire; the side wall of the annular hole is communicated with the pores of the strip-shaped sound-absorbing cotton, so that the annular main sound-absorbing cavity and a large number of porous sound-absorbing cavities are communicated.

6. A pneumatic tire having a tire noise reduction system as defined in claim 5, wherein, The line connecting the center of gravity of the annular hole and the center of the tire tread is perpendicular to the center auxiliary line where the cross-sectional width of the tire is located; the annular hole accounts for 10-50% of the cross-sectional area of the strip-shaped sound-absorbing cotton; the apparent density of the strip-shaped sound-absorbing cotton is 5-20 kg / m 3 . 3 .

7. A pneumatic tire having a tire noise reduction system as defined in claim 5, wherein, The radius Rs of the center of the cross section of the sound-absorbing cavity needs to satisfy 4.5mm<Rs<0.5Hs-1mm.

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