Green tire refers to the radial tire with low rolling resistance, low fuel consumption and low exhaust emissions due to the application of new materials and design.stayautomobileDuring driving, energy will be consumed by various resistances, and about 20% of gasoline will be consumed by tire rolling resistance.The use of green tires can reduce the energy consumption in this regard, so as to achieve the purpose of fuel saving.
Green tires use special silica mixing technology, structural design technology and production technology to reduce rolling resistance by 20% compared with ordinary tires, reduce fuel consumption by more than 5%, effectively reduce automobile fuel consumption, enhance fuel efficiency and reduce carbon dioxide emissions without losing the basic safety performance of tires.This kind of tire can benefit both the environment and the driver. On the one hand, it can minimize the adverse impact on the environment, and on the other hand, it can save fuel costs for consumers.
Green tires have the advantages of good elasticity, low rolling resistance, low fuel consumption, low heat generation, wear resistance, puncture resistance, large bearing capacity, and comfortable riding.Compared with the traditional tires, it highlights the advantages of environmental protection, energy saving, new technology, new materials and other aspects.[1]
High environmental protection
Because of the addition of carcinogenic rubber compounds to traditional tires, they disperse into the air with the wear of tread, seriously polluting the environment. At the same time, hundreds of millions of tires are abandoned every year in the world. They not only occupy a lot of space, but also are difficult to decompose, posing a great threat to the environment. They are called“Black pollution”。With the continuous improvement of people's awareness of environmental protection, while continuing to work hard to reduce rolling resistance, they have begun to attach importance to the use of materials that do not pollute the environment to manufacture tires, and have worked hard to extend the mileage of tires to reduce the number of waste tires.After a large number of cars use green tires, it has a great effect on fuel saving and pollution reduction.The wide application of green tires will save millions of barrels a year worldwidepetroleumAnd significantly reduce CO emissions.
Low consumption
The commonly used black tires are made of standard synthetic rubber and natural rubber. When the driving temperature of the car rises, the structure and performance of its protective materials change, and the rolling resistance of the wheels also increases.Compared with ordinary tires, green tires reduce tire weight and energy consumption (hysteresis loss) of composite materials.Therefore, compared with tires of the same specification, the rolling resistance of green tires can be reduced by 22% - 35%, and thus the fuel consumption of vehicles can be reduced by 3% - 8%, so that the CO emissions of vehicles can be reduced. Other performances, such as wear resistance, low noise, dry and wet road grip, can be maintained at a good level.
Super security
By optimizing the carcass design, the green tire improves the vehicle's grip performance on smooth roads with excellent elastic tread, making driving more stable, braking distance shorter, and driving safety greatly improved.Research shows that the friction generated by green tires can reduce the braking distance of vehicles on wet or icy roads by 15%, and improve the driving performance of vehicles in winter by 10% - 15%.This is of great significance for reducing accident rate and casualties.
Design method
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Theoretically, the ways to reduce automobile fuel consumption include lightweight, reducing tire rolling resistance and using lean mixture engine.In fact, only reducing the tire rolling resistance is the most feasible green tire design approach. The research results show that the tire mold, pattern design, tire structure and materials have an impact on the tire rolling resistance.The fuel consumption to overcome the tire rolling resistance accounts for 14.4% of the total fuel consumption of the vehicle, while the rolling resistance generated by the tread alone accounts for 49% of the tire rolling resistance. The proportion of other parts is 14% of the sidewall, 11% of the carcass, 11% of the bead, 8% of the belt, and 7% of the other parts.The fuel consumption directly caused by the tread accounts for about 7.1%.Reducing the rolling resistance of tread and ensuring good wet skid resistance will be the most basic requirements for green tires.
The green tire technology mainly starts with selecting the appropriate rubber type and mixture, improving the tread compound formula, supplemented by structural design means such as thinning the carcass, optimizing the tire contour, to achieve the purpose of reducing the tire rolling resistance.It can be expected that the involvement of computer-aided design technology and the introduction of polymer molecular oriented design will undoubtedly accelerate the development process of green tires.
Structural design
Meridian, tubeless and flat are the development direction of tire structure design, and also the first choice of green tires.
Green tire tread generally consists of tread rubber and tread base rubber. The dynamic modulus of tread rubber is greater than that of tread base rubber, and the ratio of tread base rubber thickness to tread rubber thickness is 025~ 0. 70。By using the finite element method to analyze the water slick phenomenon of tires, we can design tread patterns that can significantly improve the water slick phenomenon, such as Goodyear's A quat red, Michelin's Catamaran, Bridgestone's F170C, Pirelli's P5000Drag o and other tires.
Meridian of fetal structure
The tire structure can be generally divided into two types, namely, radial structure and diagonal structure.The fundamental difference between meridian structure and oblique structure lies in the placenta.The carcass is the foundation of a tire, which is a layered structure composed of cords.The upper part of the carcass layer has a belt layer with cords arranged in a circumferential direction. This structure makes full use of the cord strength, so the ply number of radial tire is 40% - 50% less than that of bias tire.
From the design point of view, bias tires have many limitations. Due to the strong friction of cross arranged cords of bias tires, the carcass is easy to heat up, and the tread pattern wear is accelerated, the cord layout cannot provide good handling performance and ride comfort;The steel belt of radial tire has better flexibility to adapt to the irregular impact of road surface, and is durable.Its ply structure also means that there is much less friction during driving, thus obtaining longer tread life and better fuel economy.
The advantages of radial tire make it possible for tire to be tubeless.Tubeless tires have a recognized advantage. When a tire is punctured, it does not burst like a tire with an inner tube (an ordinary bias tire has an inner tube), but maintains air pressure for a period of time, thus improving safety.
Due to the special structure of radial tire carcass, the road grip of the tire is large and the effect is good during driving. Compared with the car with diagonal tire, the wear resistance of the car with radial tire can be improved by 50% - 100%, the rolling resistance can be reduced by 20% - 30%, and the fuel consumption can be saved by 6% - 8%.Because of this, the same model uses radial tires for better handling and driving comfort than diagonal tires.
When the tire section width increases, the rolling resistance decreases.This is because the rigidity of the sidewall decreases with the increase of the tire section width, while the deformation of the sidewall that has less impact on the rolling resistance increases, and the deformation of the sidewall that has greater impact on the rolling resistance decreases.In addition, with the widening of tire section width, the energy loss of main parts such as tread and belt layer decreases.Therefore, increasing the tire section width is beneficial to reducing the rolling resistance.
If the height of the filler strip at the bead part increases, the rolling resistance also increases.As the height of the filler strip increases, the volume of the material that causes hysteresis loss increases, and the energy loss at the lower part of the sidewall also increases.In addition, the increase in the height of the filler strip will reduce the deformation of the sidewall due to the increase in the rigidity of the sidewall, while the deformation of the tire face that has a greater impact on the rolling resistance will relatively increase, which will lead to an increase in the rolling resistance.At present, the design of carcass structure is developing towards low section.
Tread
When the tread radius increases, the rolling resistance of the tire can be reduced.This is because when the tread radius increases, the tire will produce plane ground flexion deformation, which reduces the strain energy generated by the flexion deformation in the direction of the tire section.In other words, the rolling resistance decreases with the increase of tread radius, which is mainly due to the reduction of energy loss of tire crown and belt.In the future, the green tire tread structure should develop in the following directions:
(1)Double tread
Double tread tire has the advantages of high speed, stability, wear resistance and low heat generation. It is generally composed of tread and tread base. Its tread and tread base rubber have different dynamic modulus and tan δ.Relevant literature points out that the dynamic modulus of tread is greater than that of tread base (≥ 8.5 MPa), tan δ is greater than 0.12, and the ratio of tread base thickness to tread thickness is 0.25-0.70.
(2) Foam tread
The foamed tread is made of foamed rubber. In addition to the general components of tread rubber, it also contains crystalline syndiotactic 1,2-polybutadiene (powder, average particle size of 60 nm), together with foaming agent, antioxidant and other additives.The test shows that the tire made of foam tread has good braking and traction performance on dry and wet roads, especially on ice, and can completely maintain driving stability, durability and low fuel consumption even in hot summer. Therefore, it is the development direction of green tire tread.
The tire structure design must be able to reduce the rolling resistance without reducing other characteristics that contradict the rolling resistance (wet skid, safety, vibration, etc.).As a specific scheme to reduce rolling resistance, it is necessary to comprehensively consider the tire shape and rubber configuration, especially the impact on the rolling resistance of belt and carcass plies made of composite materials.As a research on tire structure, we should not only rely on past intuition and experience, but also use simulation technology to accelerate the development of low rolling resistance tires.
The finite element method has adopted the energy structure equation of rubber materials for decades, which has transited from the linear elastic equation to the Mooney Rivlin equation, and recently introduced the nonlinear structure equation in the field of large deformation.As the filling rubber used in many industrial rubber materials represented by tires, the viscoelastic properties such as storage modulus, loss modulus and tan8 in the 0-100% strain field make the strain nonlinear, which is generally understood as the Payne effect (Fletcher Gint effect).Nonlinear structural equations considering this point have also been proposed in recent years.Under normal wheel rotation, strain also accounts for the majority of tire deformation, and controlling the viscoelasticity in this strain field is particularly important for controlling tire rolling resistance.In fact, by applying the nonlinear viscoelastic structural equations representing the viscoelastic properties of filled rubber in the 0-100% strain field, such as storage modulus, loss modulus and tan δ, to FEA (finite element analysis), the prediction accuracy of tire rolling resistance can be significantly improved compared with the traditional prediction.In this way, the precision and efficiency of tire structure design, new material development and formula design that reduce tire rolling resistance will be correspondingly improved.At present, the method of green tire design has been developed by simulating tire rolling resistance with finite element method.
Methods for reducing resistance
Generally, there are two basic methods to reduce tire rolling resistance:
(1) Reduce tire mass
Reducing tire mass is the fastest and most effective way to reduce tire rolling resistance.In order to ensure low tire quality, the minimum component thickness must be used on the premise of ensuring tire performance.The tire manufacturer must strictly control the process to ensure that the parts reach the minimum thickness. It is not allowed for the factory to increase the thickness of parts without authorization to solve production problems.It is also an effective way to reduce the tire mass to use lightweight materials to manufacture tire components. An obvious example is the use of aramid belt instead of steel belt.
(2) Reduce material energy efficiency
The second way to reduce tire rolling resistance is to reduce the energy loss (hysteresis loss) of tire materials.The hysteresis loss of polyester cord is relatively large, but after proper improvement, it is possible to introduce varieties with less hysteresis loss.
Material application
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In terms of material application, there are usually two basic methods to reduce tire rolling resistance: reducing tire mass and material energy consumption (hysteresis loss).[2]
Polymer system
Natural rubber (NR) is non-polar rubber. Although it has excellent electrical properties, it is easy to swell in non-polar solvents, so its oil resistance and organic solvent resistance are poor.NR molecule contains unsaturated double bonds, so its heat and oxygen aging resistance, ozone resistance and UV resistance are poor, limiting its application in some special occasions.However, the application range of NR can be greatly expanded through modification of NR.
（1）NR
NR is non-polar rubber. Although it has excellent comprehensive properties, its oil resistance, organic solvent resistance, heat and oxygen aging resistance, ozone aging resistance and UV resistance are poor, limiting its application in some special occasions.The application range of NR can be greatly expanded through modification.
a) ENR
Epoxidized natural rubber (ENR) is a special natural rubber made from natural rubber (NR) by chemical modification.Compared with NR, ENR has completely different viscoelastic and thermodynamic properties, such as excellent air tightness, adhesion, wet skid resistance and good oil resistance.ENR can be strongly combined with polar fillers (such as white carbon black). When there is no filler, ENR vulcanizate can still maintain the high modulus and tensile strength of NR.ENR 50 has good oil resistance and damping properties. When it is used in tire tread compound, without coupling agent, the strong interaction between ENR and silica is an important factor to improve the comprehensive performance of rolling resistance and wet grip. The best wear resistance can be obtained by mixing ENR 25 with silica/carbon black filler.
b) Grafted natural rubber
At present, the graft copolymerization of methyl methacrylate (MMA) and NR is the most widely studied. MMA grafted NR has high elongation, high hardness, good impact resistance, flexural cracking resistance, dynamic fatigue performance, adhesion and good fillability.In industry, it is mainly used to manufacture elastic products with good impact performance, such as the air tight layer in tubeless tires.If it is blended with styrene butadiene rubber, it can be used as bead triangle rubber compound. Its raw rubber strength and adhesion with the bead wire are significantly improved, and it can increase the stiffness of the bead wire and keep the shape of the bead wire stable.
The new development of isoprene is the synthesis of 3,4-polyisoprene rubber (high glass transition temperature).The rubber can be used together with natural rubber, styrene butadiene rubber and polybutadiene rubber to improve the grip performance.Copolymer of isoprene and butadiene has been successfully developed, and trimer of isoprene with styrene and butadiene has also been successfully studied.The tread rubber made of these rubbers has good comprehensive balance performance of rolling resistance and wet road grip.
Chinese invention patent ZL95110352.0 introduces a new technology of directly synthesizing trans-1,4-polyisoprene (TPI) powder by means of supported titanium catalyzed bulk precipitation polymerization of isoprene.It was reported that 20-25 parts TPI was used to replace the car and light truck semi steel radial tires made of the same amount of styrene butadiene rubber in the tread rubber, which achieved good comprehensive driving performance and reduced the fuel consumption by about 2.5% in the 100 km fuel consumption test.
（2）IR
The new development of IR is 3,4-polyisoprene rubber (high glass transition temperature). Its use as tread compound with NR, SBR, BR can improve the grip performance of tires.Copolymer of isoprene and butadiene, and trimer of isoprene and styrene and butadiene have been successfully developed, which can be used as tread compound to make tire have good comprehensive balance performance of rolling resistance and wet grip.Chinese invention patent (ZL 951103520) The new synthesis technology of trans-1,4-polyisoprene (TPI) powder was introduced.The passenger car and light truck radial tire produced by replacing SBR with 20~25 phr TPI in tread rubber had good comprehensive performance, and the fuel consumption was reduced by 2. 5%About 5%.
（3）SSBR
Solution polymerized styrene butadiene rubber (SSBR) is widely used in green tire tread. It can produce special varieties with different macrostructure, microstructure and chain terminal modification according to requirements.In the process of polymer production, adding certain chemicals can change the end of polymer chain link, significantly enhance the interaction between polymer and carbon black, reduce the interaction between fillers, and thus reduce the rolling resistance of tires.
The 3rd generation SSBR maximized the comprehensive properties of rubber by optimizing the combination of molecular design and chain structure. There are three main products: first, styrene isoprene butadiene copolymer (SIBR) made by introducing isoprene segments into the macromolecular chain, which combines good low-temperature performance, low rolling resistance and high grip performance,It is the most comprehensive diene synthetic rubber so far, with great market potential;Secondly, block SSBR with gradual sequence structure distribution can better balance wet skid resistance and rolling resistance;Third, silane modified SSBR has enhanced the affinity between rubber and white reinforcing agents such as white carbon black, and expensive coupling agents such as titanate can not be used or used less when matching. This environment-friendly product can meet increasingly stringent environmental requirements and conform to the development direction of modern tires.
（4）BR
The magic triangle of rolling resistance, wear resistance and wet skid resistance of automobile tires must be optimally balanced as far as possible.High cis BR can not only solve the problem of tread wear resistance, but also play its advantages in other parts of the tire.The combination of BR and SSBR as tread compound can make the tire have the best comprehensive balance performance of grip and wear, reduce rolling resistance and save fuel by 5%.The BR/SSBR tread compound uses silica and silane coupling agent.When BR content is increased to 40 phr, wear resistance can be maintained, while SSBR and white carbon black can reduce rolling resistance and improve the grip of tires on snow and wet roads.The largest amount of BR is used on the sidewall of radial tire.NR/BR blend with antioxidant 6PPD (blending ratio is 50:50) has the best crack growth resistance, good puncture resistance and long service life.BR as bead rubber can improve wear resistance and elasticity and reduce heat generation.The combination of high vinyl content BR (HVBR) and NR as carcass rubber can improve the aging resistance and anti reversion properties.
（5）IIR
The main application field of IIR is tires, accounting for more than 80% of its total consumption.With the development of tubeless tires, the demand for HIIR is increasing year by year.At present, the demand for HIIR has accounted for about 60% of the total demand for IIR.IIR has excellent air tightness and chemical resistance.
(6) Foam rubber
In order to solve the dust problem caused by studded tires, studded tires were replaced by studded tires.The important feature of studdless tires is the high friction at about 0 ℃.On wet ice, the drainage effect needs to be greatly improved. It is not enough to rely solely on the drainage effect of the pattern groove and the knife groove pattern. A new type of rubber has been developed that can improve the drainage, meshing effect and adhesive friction, of which the representative is foaming rubber.Foamed rubber refers to rubber with many micro independent bubbles.
(7) Polyurethane elastomer
Compared with rubber, polyurethane elastomer has better wear resistance, higher tear strength and wider hardness range.Cast polyurethane elastomer is the most wear-resistant elastomer at present. It has the advantages of high wear resistance, colorability, high cutting resistance, excellent oil resistance and chemical resistance, and has no toxic effect on human body. It can also be fully biodegradable without adding carbon black and aromatic oil. It is an ideal material for tire tread.Michelin's PAX run flat tire is equipped with a new lightweight polyurethane auxiliary support ring, which is about 4 kg smaller than the original rubber support ring.The key technology of using polyurethane as tire retreading material is to use nanotechnology to improve the thermal stability of polyurethane elastomer, so that its maximum use temperature can reach 120 ℃. Secondly, it is to develop low-cost, convenient and effective rubber surface treatment agents and adhesives, so that polyurethane tread and ordinary rubber can be firmly bonded together.The actual driving mileage of retreaded tires with polyurethane tread can be 1~2 times higher than that of ordinary tires. At the same time, it can eliminate the environmental pollution caused by a large amount of carbon black and aromatic oil, which is a new way to improve the performance of retreaded tires.
Cord reinforcement system
(1) Rayon
Due to the good dimensional stability of rayon, it can be used as the carcass framework material of radial tire to obtain excellent handling performance, so it is still often used for high-performance tires and run flat tires at present.
(2) Nylon
Nylon cord is mainly used for bias tires. The latest new products are mainly poly (adipic acid butylene diamine) fiber and DuPont HYTEN high-strength polyamide fiber.Poly (adipic acid butylene diamine) fiber (nylon 46) has the characteristics of high melting point, heat shrinking and high modulus, unlike nylon 6 and nylon 66, which are easy to melt the cord due to heat generation and reduce the durability of tires.Using HYTEN as carcass framework material of radial tire can make the tire have good durability and low heat generation, and can reduce tire quality.Goodyear's trial production of aircraft tires with large diameter HYTEN cord as the buffer layer and carcass ply can reduce the ply and compound by about 17% and 45% respectively, so as to reduce the standing wave phenomenon, the shear deformation of the ply and the heat generation.
(3) Polyester
Polyester is one of the fibers that are developing steadily in the rubber industry.In the 1980s, dimensional stable polyester (DSP) was successfully developed. The use of dimensional stable polyester cord fabric to manufacture radial tires can eliminate the post vulcanization inflation process, and solve the appearance problem of concave sidewalls caused by thermal shrinkage.The raw material cost of polyester for light truck tire is 35% lower than that of rayon.Since polyester has higher strength than rayon, it can usually reduce the number of carcass layers when using polyester.
(4) Steel wire
The biggest feature of steel wire is its high strength.In recent years, the main new products of steel wire framework materials for tires are as follows.
a) High strength steel wire
In recent years, high-strength steel cord is widely used in tires, and its strength is 20%~40% higher than that of ordinary steel cord.At present, it is still under development with strength up to 4Ultra high strength steel wire of 0 GPa.
b) Ultra fine and super strong steel wire
Goodyear has developed ultra-fine and super strong steel wires (7000 wires can be arranged within 25 mm) for running flat tyres.The successful development of this ultra-fine steel cord has pioneered the use of steel cord in car tire carcass.
(5) Aramid
Aramid fiber has very high thermal stability, oxidative degradation occurs at 400~430 ℃, melting point is up to 500 ℃, and modulus is very high.
(6) Compound cord
Up to now, there is no commercially available cord that can fully meet the various performance requirements of tires.In order to make full use of the advantages of various cords and overcome their disadvantages, people have proposed the method of using composite cords.A patent has been proposed to manufacture nylon/polyester composite cord with nylon filament as the surface layer and polyester filament as the core layer. The composite cord combines the elasticity and strength of polyester cord and the good adhesion of nylon cord.Compared with aramid cord, the composite cord twisted by 1~2 strands of aramid and 1 strand of nylon or polyester has the following characteristics: high fatigue resistance and elongation at break, low modulus, controllable shrinkage, better or equivalent strength cost ratio.Compared with aramid/nylon composite cord, aramid/polyester composite cord has slightly lower tensile properties, much higher modulus, smaller permanent deformation and poor adhesion.At present, some large construction machinery tires use composite cords.
Filling reinforcement system
In recent years, new fillers, such as high structure carbon black, nano structure carbon black, white carbon black and carbon black white biphase filler, have been successfully developed. On the premise of maintaining low rolling resistance of tire tread, they have improved the wear resistance of tires, improved the comprehensive performance of tires, and promoted the development of green tires.
(1) Carbon black
a) Carbon black with high performance and low hysteresis loss
High performance carbon black is characterized by small particle size, suitable structure, narrow aggregate size distribution and high surface activity, while low hysteresis loss carbon black is characterized by high structure, wide aggregate size distribution and high surface activity.
b) Nanostructured carbon black
Nanostructured carbon black is produced by an improved furnace process.Compared with traditional carbon black, nanostructured carbon black has higher surface roughness and activity.The higher surface activity is mainly related to the small crystalline particles with highly disordered cross-linking.Such crystalline particles have a large number of edges, become active fields with high surface energy, and have strong interactions with polymers.
(2) White carbon black
Silica is a highly dispersed amorphous powder or flocculent powder with high electrical insulation, porosity and water absorption.The original particle size is less than 3 µ m, so the specific surface area is large.The special polymer and white carbon black/silane system used in the tread can obtain traction performance and braking performance on wet roads, and reduce rolling resistance.In the original car tire market in Europe, more than 80% of the tires with white carbon black/silane filling system have been used.The significant improvement of the performance of modern winter tires also depends on the use of silica/silane system in tread rubber.The special high dispersion white carbon black and high structure fine particle carbon black used for truck tires can reduce rolling resistance while maintaining wear resistance.
(3) Carbon black silica biphase filler
Carbon black white carbon black biphase filler improves the interaction between elastomer and filler, reduces the interaction between filler and filler, and can greatly reduce the rolling resistance of tire and improve traction, but does not reduce the wear resistance of traditional carbon black [20].
(4) New filler based on starch (BoT red)
BoT red is a new type of filler based on starch. Corn starch derivatives are extracted from corn, and then transformed into micro drops, which are treated and converted into biopolymer fillers.BoT red is a spherical particle, which is convenient for minimizing mechanical energy and reducing rolling resistance.Compared with the previous generation of products, the GT3 green tire manufactured by Goodyear with BoT red has a 5% increase in water skid resistance, a 100g reduction in mass and a 10% reduction in rolling resistance.
(5) Short fiber
The application of short fiber in the tire tread has the following two main effects on the tire rolling resistance: a) improve the rigidity of the tire, so that the subsidence of the tire under the same load during driving is significantly reduced, that is, the deformation of the tire is reduced, thus reducing the rolling resistance;b) Short fiber used in tread compound can not only improve the rigidity of tread, but also reduce the friction coefficient of tread and the rolling resistance.
Future development
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Green tires reflect the historical trend of promoting environmental protection and energy conservation and promoting the sustainable development of the global economy.In 1997, the market share of green tires in European passenger tires reached 60%, and further increased to 90% in 2002.The development of green tires is the focus of the world's major tire enterprises, and the development prospects of green tires are very broad.[3]
