Pulley tensioner for an oil wet belt drive
A tensioner ( 1 ) for a belt drive, comprises a base ( 2 ) defining an axis (A), a mobile eccentric element ( 3 ) hinged about axis (A) and loaded by a spring ( 5 ), a pulley ( 4 ) idly connected to the mobile element ( 3 ). Specifically, the pulley ( 4 ) defines a single body with the external ring of a rolling bearing ( 6 ) mounted on the mobile element ( 3 ) and the spring ( 5 ) is helical and presents a square or rectangular cross section.
1. A tensioner comprising a base defining an axis (A), a mobile eccentric element hinged about said axis (A) and loaded by a first spring, a pulley for an oil wet belt drive idly connected to said mobile element, wherein said pulley defines a single body with the external ring of a rolling bearing mounted onto said mobile eccentric element, the mobile eccentric element including an annular groove radially disposed between axis (A) and an inner ring of the roller bearing, and said first spring is helical and presents a square or rectangular cross section turns and is housed in a cylindrical manner within the annular groove, and a protection bushing interposed between an inside surface of the first spring and the annular groove.
2. The tensioner according to claim 1 , wherein said base comprises a pivot defining said axis (A) and having an outer layer hardened by means of a surface treatment and coupled to said mobile eccentric element.
3. The tensioner according to claim 2 , wherein the hardness of said outer layer is higher than 600 HV.
4. The tensioner according to claim 3 , wherein the hardening of the outer layer is obtained by a nickel-plating treatment.
5. The tensioner according to claim 1 wherein said roller bearing is fitted onto said mobile eccentric element and in that said bearing and said mobile eccentric element are made of steel.
6. The tensioner according to claim 1 said base comprises a plate having a hardened surface, a first friction element arranged between said mobile eccentric element and said plate and loaded by means of a second spring, and a second friction element loaded by means of said second spring.
7. The tensioner according to claim 6 , wherein said second friction element is connected in a way that is rigid to rotation and slidable to translation to a constraint element carried by one of said base or said mobile eccentric element.
8. The tensioner according to claim 7 , wherein said second spring is arranged between said constraint element and said second friction element.
9. The tensioner according to claim 8 , wherein said second friction element is a disc comprising a plurality of projections which are oriented to be parallel to said axis (A) and slide in corresponding seats defined by said constraint element.
10. The tensioner according to claim 6 wherein at least one of said first and second friction elements comprises a polyamide.
11. The tensioner according to claim 6 further including a pin mounted onto the mobile eccentric element and a slot formed in a cover plate with the pin being arranged parallel to said axis (A) and radially external to the second friction element, wherein said pin and said slot cooperatively define two maximum angular positions for the rotation of said mobile eccentric element with respect to said base, said pin being positioned on said mobile eccentric element on an opposite axial side relative to said plate and said first friction element.
12. The tensioner according to claim 1 wherein said bearing is a sealed bearing containing a lubricating agent.