Tensioner for an accessory transmission of an internal combustion engine
A tensioner for a belt transmission of a motor vehicle engine has a fixed part configured to be constrained to the engine and provided with a pin defining a rotation axis (A), an arm having a hub portion hinged on the pin and rotatable about the axis (A) and an opposite portion rotatably supporting a pulley configured to cooperate with a transmission belt, a main spring interposed between the fixed part and the arm to exert a thrust on the arm such as to rotate the arm towards the belt, a roller bearing supporting the arm on the pin, and a pair of damping devices exerting on the arm opposite actions so as to minimize the load on the bearing.
1. A tensioner for a belt transmission of a motor vehicle engine, comprising:
a fixed part comprising a base configured to be fixedly secured with respect to the engine and a pin defining a rotation axis (A);
an arm having a hub portion hinged on the pin and rotatable about the axis (A) and an opposite portion rotatably supporting a pulley configured to cooperate with a transmission belt;
a main spring interposed between the fixed part and the arm to exert on the arm a thrust such as to rotate said arm towards the belt;
at least one rolling bearing interposed between the arm and the pin; and damping means for damping the oscillations of the arm about the pin,
wherein said damping means comprise a first damping device and a second damping device exerting opposite actions on the arm.
2. The tensioner as claimed in claim 1 , wherein said first and second damping device have an axial action.
3. The tensioner as claimed in claim 1 , wherein said first and second damping device comprise respective spring elements exerting axial loads in opposite directions to one other.
4. The tensioner as claimed in claim 3 , wherein the axial actions of said spring elements and the axial action of the main spring are substantially in equilibrium with each other so as to minimize the axial load on said at least one rolling bearing.
5. The tensioner as claimed in claim 1 , wherein the damping devices comprise respective damping rings cooperating in a sliding manner with respective surfaces of the arm under the action of the respective spring elements.
6. The tensioner as claimed in claim 1 , wherein said spring element are disc springs.
7. The tensioner as claimed in claim 1 , wherein said hub portion comprises an outer cylindrical wall and an inner cylindrical wall delimiting between them an annular cavity which houses said main spring, said bearings being arranged radially between said pin and said inner cylindrical wall.
8. The tensioner as claimed in claim 7 , wherein the first damping device is arranged between the base and a head surface of the outer wall, and the second damping device is arranged between an end cap integral with the pin and an inner shoulder of the inner wall.
9. The tensioner according to claim 8 , wherein said at least one bearing is in axial abutment with said shoulder.
10. The tensioner according to claim 7 to 9 , comprising annular sealing elements configured to protect the respective damping devices from dirt.