Different mechanism to open sliding side doors of commercial vehicles part of which has been adapted to transport passengers too, both as public and private/family vehicles, are already known. As far as known mechanism are concerned, the door is anchored to the bodywork and is guided not only at its lower and upper part, but also at its middle part. When this solution is adopted, designers have to provide a more or less large guide all along the side of the vehicle, so that the overall esthetical aspect of the vehicle is highly affected. Besides, known sliding doors are mounted on vehicles the bodywork of which is provided with the central side upright, which stops both the front door and the sliding side door However, the central upright reduces the space available to reach the seats, more in particular the backseats, so that it would be better to count on a side opening completely free, that is without upright. It is to be noted that the lack of the central upright is a problem for the stopping of the front door since the stopping is to be achieved against the rear sliding door, as well as for the achievement of a mechanism that allows to open the sliding door even if the front door is closed and rests against it.

It is an object of the present invention to provide a mechanism adapted to open a sliding door that overcomes the aforementioned drawbacks.

Said object is achieved by means of a mechanism adapted to open the side sliding door or a motor vehicle presenting the characteristics set forth in claim 1.

Additional characteristics and advantages will become more clear from the following description referring to the appended drawings provided as non- restrictive example and in which: figure 1 is a perspective view of the arm mechanisms according to the invention, housed in the lower side member of a motor vehicle and connected to a sliding door. figures 2 to 5 are schematic views of the mechanism in figure 1 with the sliding door shown in its different operational positions, from a completely closed position to the completely open position ; figures from 6 to 10 are perspective view of an enlarged detail of the arm mechanism in figure 1 in its different operational position.

The following description refers to a motor vehicle without central upright at its side, and in which the front profile of the side, rear, sliding door serves as stop for the weather strips of the front door. With reference to the figures, reference number 1 indicates a sliding door of a motor vehicle, shown in a schematic view, while reference number 2 indicates the part of the lower side member, which experts in the field call"sill". Inside the sill 2 there is an elongated space where a wheeled trolley 3 (figures 6-8) slides according to a well known technique. Hinged to the trolley 3 at points 7 and 8 there is an end of two lower arms so that they can rotate around an axle which is basically perpendicular to the plane defined by the flat car of the bodywork. The other two ends of the arms 9 and 10 are rotatably engaged around a single axle with joints 12 and 13, to the lower part of the sliding door.

The run of the trolleys 3 and 4 is limited, at the opening of the door (right side in the drawing), by a stop 17 provided with a system of engagement, for example a hook (not shown) of the trolley 3 and, at the closing of the door, by the bottom wall 19 of the space 2a, in order to get locked at the stop of the front doorlock (not shown). A microswitch allows to adjust both mechanically and electrically both the engagement and the release of the trolley 3 by means of the locking system 18.

On the external wall of the space 2a, in front of the trolley 3, there is a wall 20 the length of which is basically equal to the length of the space 2a where the trolley 3 slides, and the front and rear ends 21 and 22 of which are curved towards the inner part of the space 2a. The height of the wall shall be calculated so that it will not interfere with the arms 9 and 10 when they rotate on their hinges 8 and 9. A bridge 23 is fixed to the lower wall of the front arm 10 by means of a axle 25. At its ends there are two small wheels or rollers 27 and 28 covered in antifriction material, and it is basically perpendicular to the axis of the arm supporting it. The diameter of the rollers 27 and 28 is such that it interacts with the external surface of the wall 20 while the arm 10 is rotating as a consequence of the opening of the sliding door.

Even if no detailed description is provided, the same mechanism can be used in a similar elongated space, made in the upper side member of the bodywork so that it can support and guide the sliding door not only at its lower part but also at its upper part.

The mechanism for sliding doors according to the invention works as follows By means of the handle (not shown) on the door 1, the locks (in the case two locks are used, a front lock and a rear lock) are unlocked and the door makes a circular movement being supported by the arms 9 and 10 which make a basically 90 degrees rotation on the hinges 7 and 8 and reach a position which is basically perpendicular to the body side of the motor vehicle. The roller 27 guides the movement of the arm 10 (and consequently that of the whole door) and slides on the front curved part 21 of the wall 20 (figures 6 and 7) When the arm 10 has reached a position which is basically perpendicular to the body side (and the arm 9 has reached the same position too), both rollers come into contact with the wall 20 thus preventing an additional rotation of the arm itself.

At this point, a further action on the handle of the door makes the trolley 3 slide on the wheels 4 inside the space 2a, so that the door 1 translates along the body side and the rollers 27 and 28 slide on the flat part of the wall 20 (figures 3 and 8).

When the trolley 3 bumps against the stop 17 (figure 4) being engaged by it as described above, the roller 28 reaches the rear curved part 21 of the wall 20, so that being no longer supported on said wall, allows arm 10, and therefore arm 9, to further rotate so that the door 1 moves further and the door opening widens (figures 5 and 10).

The adjustment of the length of the arms 9 and 10 as well as that of the space 2a allows to determinate how much can the door move.