Two-arm belt tensioner for a belt drive
A belt tensioner for a belt drive is designed to connect an engine shaft of an internal-combustion engine to a reversible electric machine which has the function of starting motor and current generator; the belt tensioner comprises a fixed part and a pair of arms, hinged on a common pin carried by the fixed part and provided with respective idle pulleys, and a spring, which forces the two arms towards one another so as to load the pulleys elastically against respective branches of the belt. The two arms of the belt tensioner are provided with respective first arrest elements, which are designed to interact with the fixed portion to define respective positions of arrest of the arms themselves under the action of the spring, and respective second arrest elements, which are designed to interact with the fixed portion to define respective positions of end-of-travel of the arms under the action of the pull of the belt.
1. A two-arm belt tensioner for a belt drive, comprising:
a fixed portion, designed to be fixed to a supporting structure;
a first arm and a second arm, carried by said fixed portion and hinged thereto about a common axis;
a first pulley and a second pulley, mounted idle on respective ends of said arms and designed to co-operate with respective branches of a belt of said drive; and
elastic means, which force said arms towards one another to maintain said pulleys in contact with said respective branches of the belt, said arms comprising respective first arrest elements, which are designed to interact with said fixed portion to define respective first positions of arrest of said arms under the action of said elastic means, and respective second arrest elements, which are designed to interact with said fixed portion to define respective second positions of end-of-travel of said arms under the action of the pull of said belt, said fixed portion comprising a base plate, a pin fixed to said plate and defining said common axis of rotation of the two arms, said belt tensioner being characterized in that said fixed portion includes a single appendage fixedly attached to said base plate, wherein the single appendage is non-movable relative to the base plate, and wherein the single appendage defines a stop for said first and second arrest elements of said arms so as to define for each arm a travel limited between a first position of arrest and a second position of end-of-travel.
2. The belt tensioner according to claim 1 , characterized in that said at least one of said first and second arrest elements of said arms comprises a radial projection, which extends from the respective arm and is designed to interact with said appendage of said fixed portion.
3. The belt tensioner according to claim 2 , characterized in that at least one of said arms comprises a hub, which houses at least partially said base plate and is provided with an opening, through which there comes out said appendage, at least one of said arrest elements being defined by an end contrast element delimiting said opening.
4. The belt tensioner according to according to claim 1 , characterized in that said first and second arrest elements are provided with respective buffers made of elastic material for absorbing the impact with said fixed portion.
5. The belt tensioner according to claim 1 , characterized in that said elastic means comprise a spiral spring and in that one of said arms comprises a cup-shaped hub, which houses said spring said spring being constrained, with its own outer end, to said hub and, with its own inner end, to the other arm.
6. A belt drive for connecting a reversible electric machine to an engine shaft of an internal-combustion engine, said electric machine being operable as an electric machine for starting said internal-combustion engine or as generator, said drive comprising:
at least one first pulley fitted on the engine shaft of said internal-combustion engine;
a second pulley fitted on a shaft of said electric machine; and
a belt wound around said pulleys said belt comprising:
a first branch and a second branch set respectively between said first pulley and said second pulley and between said second pulley and said first pulley in the direction of motion of the belt itself; and
a two-arm belt tensioner, which comprises:
a fixed portion, designed to be fixed to a supporting structure;
a first arm and a second arm, carried by said fixed portion and hinged thereto about a common axis;
a first pulley and a second pulley, mounted idle on respective ends of said arms and designed to co-operate respectively with said first branch and with said second branch of said belt; and
elastic means, which force said arms towards one another to maintain said pulleys in contact with said respective branches of the belt;
said arms comprising respective first arrest elements, which are designed to interact with said fixed portion to define respective first positions of arrest of said arms under the action of said elastic means; and
respective second arrest elements, which are designed to interact with said fixed portion to define respective second positions of end-of-travel of said arms under the action of the pull of said belt;
said fixed portion comprising a base plate, a pin fixed to said plate and defining said common axis of rotation of the two arms, said belt drive being characterised in that said fixed portion includes a single appendage fixedly attached to said base plate, wherein the single appendage is non-movable relative to the base plate, and wherein the single appendage defines a stop for said first and second arrest elements of said arms so as to define for each arm a travel limited between a first position of arrest and a second position of end-of-travel.
7. A belt tensioner according to claim 6 , characterized in that said elastic means have a rigidity calculated so as to bring about a rotation of each arm of the tensioner up to the respective second position of arrest in the presence of a maximum value of tension of the respective branch of the belt.