Pulley tensioner for an oil wet belt drive
A tensioner ( 1 ) for a belt drive comprises a base( 2, 3 ) defining an axis (A), a mobile element ( 4 ) hinged onto axis (A) and defining a guiding surface ( 22 ), an elastic helical element ( 18 ) having a square or rectangular cross section for actuating the mobile element ( 4 ) and an idle pulley ( 5 ) surrounding the guiding surface ( 22 ). The tensioner ( 1 ) further comprises a journal bearing ( 4, 29, 32, 33 ) for supporting the pulley ( 5 ) on the guiding surface ( 22 ).
1. A tensioner for a belt drive comprising: a base defining an axis (A), a mobile element hinged to move about said axis (A) and including a guiding surface, an elastic element for actuating said mobile element, a pulley mounted on said mobile element about said guiding surface and rotatable about a second axis (B) offset with respect to said axis (A), a locking element for axially fastening said mobile element to said base, an annular friction element interposed between said mobile element and said locking element, a spring interposed between said friction element and one of said either the mobile element or the locking element and providing an axially directed force on said annular friction element, and a journal bearing adapted to be fed by oil to support said pulley on said guiding surface and wherein said elastic element is helical and presents a square or rectangular cross section.
2. The tensioner according to claim 1 , further including a fluid seal to seal the oil fed to said journal bearing arranged on the same side as said spring with respect to said friction element.
3. The tensioner according to claim 2 , wherein said fluid seal comprises an O-ring.
4. The tensioner according to claim 2 further including a labyrinth seal defined between said friction element and the other of either the mobile element or the locking element that is not in direct contact with said spring.
5. The tensioner according to claim 1 wherein said pulley is formed from steel, and a ratio between a maximum thickness (S) and a maximum diameter (D) of said pulley is greater than 7.5%.
6. The tensioner according to claim 5 , wherein said ratio between maximum thickness (S) and maximum diameter (D) of said pulley is greater than 10%.
7. The tensioner according to claim 1 wherein the mobile element is made of a material having a first thermal expansion coefficient and the pulley is made of a material having a second thermal expansion coefficient that is lower than said first thermal expansion coefficient.
8. The tensioner according to claim 1 wherein the journal bearing comprises a first duct perpendicular to said axis (A) and defining an outlet for feeding oil onto said guiding surface.
9. The tensioner according to claim 8 , wherein the first duct is defined by said mobile element.
10. The tensioner according to claim 8 wherein the base comprises a pivot member that is coaxial to said axis (A) and includes a second duct adapted to be fed by a flow rate of pressurised fluid and being fluidically connected to said first duct.
11. The tensioner according to claim 10 , wherein said mobile element is radially supported on said pivot by means of a bushing ( 8 ) defining a passage to allow the passage of oil between said first duct and said second duct ( 29 ).
12. The tensioner according to claim 8 further including a second fluid seal interposed between said mobile element and said base, said first duct being interposed between said first and second fluid seals.
13. The tensioner according to claim 8 wherein said guiding surface is axially delimited by a first and a second shoulder and defines an axially symmetric recess fluidly connected to said first duct to apply a symmetric action on said pulley.
14. The tensioner according to claim 13 , further including a ring axially interposed between one of the said first and second shoulders and said pulley.
15. The tensioner according to claim 14 , wherein at least one of said first and second shoulders is defined by an elastic ring.
16. The tensioner according to claim 8 wherein said first duct precedes the resultant of the action of said belt on said pulley by an angle comprised between 60° and 130°.
17. The tensioner according to claim 1 further including a second friction element cooperating in relative motion with a contact surface arranged transversally with respect to said axis (A), said spring maintaining contact with said friction element and said contact surface.
18. The tensioner according to claim 17 , wherein said second friction element presents at least one impression facing said contact surface.
19. The tensioner according to claim 1 wherein said base comprises a component having a surface hardened by means of a surface treatment.