Belt tensioner

A tensioner with a longitudinal axis, comprising:

• a hollow body provided with an opening and a bottom, the hollow body comprising a fluid;
• a sleeve arranged around the hollow body,
• an axis,
• a first guide means for said axis this first guide means being attached to the hollow body at the opening thereof;
• a second guide means for said axis, this second guide means being in the form of a tube that defines an inner volume wherein said axis is intended to move and an outer volume that is outside said second guide means within the hollow body;
• a first cup fixedly mounted on said axis between the first and second guide means of said axis;
• a second cup mounted at the bottom;
• an elastic return means arranged around the second guide means so that there is a non-zero distance, taken radially, between the elastic return means and the second guide means, said elastic return means being held between the first cup and the second cup;
• a valve comprising a seat mounted between one end of the second guide means and the bottom of the hollow body, with which valve at least one fluid communication channel is associated to allow the passage of a fluid contained in the hollow body between the outer volume of the second guide means and the inner volume of said second guide means,
• characterised in that:
• said bottom comprises a central zone, a peripheral zone that is raised relative to the central zone and an intermediate zone connecting the central zone to the peripheral zone;
• the first cup comprises a first portion in front of the peripheral zone and a second portion that is in front of the intermediate zone and is in contact with a base of the seat, this base itself being in contact with the central zone;
• the elastic return means is designed to bear on the first portion of the first cup;
• said at least one fluid communication channel is arranged to open in front of the second portion of the first cup at a non-zero distance from this second portion, this arrangement allowing a fluid region of the hollow body to be defined around the second guide means up to said at least communication channel, said fluid region being free of any obstacle.