V-ribbed power transmission belt

Endless belt power transmission systems or components – Friction drive belt – Including groove – openings or pockets formed in belt surface...

Reexamination Certificate

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Details

C474S237000

Reexamination Certificate

active

06361462

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to power transmission belts and, more particularly, to a power transmission belt having a plurality of laterally spaced ribs extending in a lengthwise direction.
2. Background Art
It is known to use V-belts in automobiles to drive various accessories from the engine crank shaft. Several belts may be independently driven by the crank shaft. In one exemplary engine construction, one belt drives an alternator and a blower, a separate belt drives a power steering unit, and a third belt drives cooling equipment.
There has been a trend to reduce the weight and size of cars to reduce fuel requirements. In many of these cars, a V-ribbed belt is used having a body with longitudinally extending, load carrying cords and a plurality of V-shaped ribs spaced laterally from each other and extending longitudinally on one of the inside and outside of the belt body. The other of the inside and outside of the belt body has one or two plies of rubber-impregnated canvas cloth thereon. The belt can be arranged in a serpentine configuration to cooperate with several accessory pulleys. The belt may be tensioned by an idler pulley which is pressed against the non-ribbed surface. This non-ribbed surface is also used to drive one or more accessories.
Generally, the non-ribbed surface does not have the power transmission capability of the ribbed surface. Frictional wearing of the non-ribbed or ribbed surface may result in a lowering of the belt tension, which could result in slippage. When this occurs, the belt may be incapable of positive power transmission under a heavy load.
To overcome this problem, it is known to use double V-ribbed belts wherein a plurality of laterally spaced and longitudinally extending ribs are provided on both the inside and outside of the belt body. Typically, the ribbed portions on the inside and outside of the belt have identical rib pitch, rib height, and rib shape. Load carrying cords are embedded in the belt body between the inner and outer ribs.
A double V-ribbed belt is commonly used in compact automobile engine compartments. These engines may generate sufficient heat in these smaller compartments that the belts are required to operate in a high temperature environment. It is known to use natural rubber, styrene-butadiene rubber, and chloroprene rubber for belts in this environment. However, these belts using these rubbers are prone to premature cracking. Typically, the cracking occurs in the compression layer of the belt with the rubber therein in a hardened state.
Research has been done to improve the heat resistance of chloroprene rubber. Some improvement has resulted from these efforts. However, the improvement has been limited and in many environments the performance of the improved chloroprene rubber is still inadequate.
Studies have also been undertaken to use, as an alternative, rubber such as chlorosulfonated polyethylene rubber, hydrogenated nitrile rubber, or fluoro rubber. With a main skeleton therein that is highly saturated or completely saturated, these rubbers have excellent heat resistance. Among these rubbers, it is known that chlorosulfonated polyethylene is comparable to chloroprene rubber in terms of dynamic fatigue properties, wear resistance, and oil resistance. However, chlorosulfonated polyethylene has diminished water resistance characteristics resulting from the effects of the vulcanization process, particularly with an acid receiving agent. Typically, oxides such as MgO and PbO have been used as the acid receiving agent for chlorosulfonated polyethylene.
However, when an acid receiving agent having a lead compound, such as PbO and Pb
3
O
4
is used, while water resistance is improved, there arises a problem with respect to pollution and sanitation attributable to the lead.
When MgO is used as an acid receiving agent, the water resistance is significantly deteriorated by MgCl
2
during the crosslinking reaction. The resulting rubber may not be suitable for use in a power transmission belt.
On the other hand, while it is possible to obtain a composition with good water resistance using an epoxy-type acid receiving agent other than the metal oxide, the resulting product has a bad odor, making it unpleasant to those handling the composition.
While power transmission belts, made as described above, may have significantly improved belt running life and excellent heat resistance under high temperature conditions compared with belts using chloroprene rubber, these belts may have an unacceptably low life in a low temperature environment, such as at −30° C. or lower. This may be attributable to the fact that chlorosulfonated polyethylene rubber is formed by chlorosulfonated polyethylene and contains chlorine. The cohesive energy of chlorine is increased at a low temperature to cause hardening of the rubber. At low temperatures, the rubber may lack elasticity and be prone to cracking.
Ethylene-&agr;-olefin elastomers, such as ethylene-propylene rubber (EPR) and ethylene-propylene diene rubber (EPDM) are polymers having excellent heat resistance and cold resistance. These elastomers are also relatively inexpensive. However, these elastomers have a low resistance to oil and as such are not commonly used in applications where they will encounter oil. Since dry frictional V-ribbed belts are prone to slipping when exposed to a significant amount of oil, their transmission capability is deteriorated, making them generally impractical for this environment. However, use of these elastomers in a power transmission environment has been studied, as disclosed in Japanese Patent Laid-Open Hei 345948/1994.
Ethylene-propylene rubber has a relatively low tear strength, which is reduced even further by using a peroxide crosslinking system. As a result, the load carrying cords tend to pop out during operation. It is also difficult to effectively increase the degree of vulcanization in the rubber using a sulfur crosslinking system, so that abrasion may be significant during operation. Abrasion dust tends to accumulate at the base of the ribs, and may cause adhesive wear. This also potentially leads to a significant noise generation problem. While using EPDM with a large number of double bonds in the molecules may increase the degree of vulcanization and adhesive wear properties, it tends to lower heat resistance.
SUMMARY OF THE INVENTION
In one form, the invention is directed to a power transmission belt having a body with a length, an inside, an outside, and laterally spaced sides. The body has a bonding rubber layer in which elongate load carrying cords are embedded to extend lengthwise of the body. The body has a first layer on the inside of the bonding rubber layer in which a plurality of laterally spaced ribs are formed extending lengthwise of the body, and a second layer on the outside of the bonding rubber layer in which a plurality of laterally spaced ribs are formed extending lengthwise of the body. The bonding rubber layer has a sulfur-crosslinked rubber composition including an ethylene-&agr;-olefin elastomer. At least one of the first and second layers has a crosslinking product that is an organic peroxide-crosslinked rubber composition including an ethylene-&agr;-olefin elastomer.
In one form, the first and second layers both have a crosslinking product including an organic peroxide-crosslinked rubber composition with an ethylene-&agr;-olefin elastomer.
In one form, there is no reinforcing cloth on any of the inside, outside, or laterally spaced sides of the body.
The ethylene-&agr;-olefin elastomer in the first and second layers may be at least one of ethylene-propylene-diene monomer (EPDM) and ethylene-propylene rubber (EPR).
The diene monomer may be at least one of dicyclopentadiene, methylene norbornene, ethylidene norbornene, 1,4-hexadiene, and cyclooctadiene.
The organic peroxide may be at least one of dicumyl peroxide, di-t-butyl peroxide, t-butylcumyl peroxide, benzoyl peroxide, 1,3-bis-(t-butyl-peroxyisopropyl) benzene, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, 2,5-

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